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SWIM22 - 22 nd Salt Water Intrusion MeetingTITLEGerson Cardoso da Silva Jr.,Suzana Maria Gico de Lima MontenegroEDITORS1º. EditionRIO DE JANEIRO, BRAZIL2012META MARKETING E EVENTOSPUBLISHER978-85-63243-03-4ISBN

Organizing CommitteeGerson Cardoso da Silva JuniorDepartment of Geology, Institute of GeosciencesFederal University of Rio de JaneiroRio de Janeiro, BrazilSuzana Maria Gico MontenegroDepartment of Civil EngineeringFederal University of PernambucoRecife, BrazilTeresa Condesso de MeloCVRM Geo-Systems Centre - ISTLisbon Technical UniversityLisbon, PortugalEmilio CustodioDepartment of Geotechnical Engineering and Geo-Sciences (ETCG)Polytechnic University of CataloniaBarcelona, SpainJohannes MichaelsenCONSULAQUA Beratungsgesellschaft mbHHamburg, GermanyKlaus HinsbyGeological Survey of Denmark and Greenland (GEUS)Copenhagen, DenmarkClifford VossUS Geological SurveyMenloPark, CA, USA

Local Supporting Organizing TeamMaria da Gloria AlvesUENF - Civil Engineering Laboratory, Northern Rio de Janeiro StateUniversity, Campos, BrazilElisa de Souza BentoINEA – Rio de Janeiro Environmental Institute, Rio de Janeiro,BrazilKátia Leite MansurDepartment of Geology, Institute of GeosciencesFederal University of Rio de JaneiroRio de Janeiro, BrazilScientific CommitteeAlice AureliInternational Hydrological Programme, UNESCO, ParisGiovanni BarrocuUniversity of CagliaryCagliary, ItalyEmilia BocanegraNational University of Mar Del PlataMar del Plata, ArgentinaMari Carmen CabreraUniversity of Las PalmasLas Palmas, SpainRui CoutinhoCVARG - University of AzoresPonta Delgada, Azores, PortugalJosé Virgílio CruzUniversity of AzoresPonta Delgada, Azores, PortugalEmilio CustodioTechnical University of CataloniaBarcelona, Spain

Gualbert Oude EssinkDeltaresThe NetherlandsChristian LangevinUS Geological SurveyFlorida, USAMarisol ManzanoTechnical University of CartagenaCartagena, SpainTeresa Condesso de MeloCVRM Geo-Systems Centre - ISTLisbon, PortugalJorge MolineroAmphos XXI Consulting S.L.Barcelona, SpainMaurizio PolemioBari Technical UniversityBari, ItalyVincent E.A. PostVrije UniversiteitAmsterdam, The NetherlandsD. PostmaGeological Survey of Denmark and Greenland (GEUS)Copenhagen, DenmarkAntonio PulidoUniversity of AlmeriaSpainLuis RibeiroInstituto Superior TécnicoLisboa, PortugalEmanuel Vieira da Silva-FilhoFluminense Federal UniversityNiteroi, BrazilTibor StigterInstituto Superior TécnicoLisbon, Portugal

Peter StuyfzandKiwa Water Research, Nieuwegeinand Vrije Universiteit AmsterdamThe NetherlandsLuis VivesNational University of Buenos Aires ProvinceAzul, ArgentinaClifford VossUS Geological SurveyMenloParkCA, USAKristine WalraevensUniversity of GhentGhent, BelgiumAdrian WernerFlinders UniversitySouth AustraliaYoram YechieliGeological Survey IsraelSueli YoshinagaUNICAMP - Campinas State UniversitySão Paulo, BrazilShaul SorekBen-Gurion University of the NEGEVIsrael

Conference Topics1. Keynote Lecture2. Effects of sea level rise and climate change over salt water interfaces3. Geophysical methods to characterise the distribution and dynamics ofsaline groundwater4. Hydrogeochemical and isotopic methods to study the origin and dynamicsof saline groundwater5. Management of aquifers with saline groundwater. Salinizationprevention, control and remediation6. New approaches on modelling (general methods and solution of realcases)7. Selected case studies8. Understanding of saline water hydrodynamics in aquifers (theoretical andnumerical aspects)

PrefaceWelcome to the 22 nd Salt Water Intrusion Meeting,to be held from 17 th to22 nd of June 2012 in Búzios, Brazil. It will be co-organized by the GeologyDepartment of Federal University of Rio de Janeiro (UFRJ), the EngineeringSchool of Federal University of Pernambuco (UFPE) and the BrazilianGroundwater Association (ABAS-RJ), with the collaboration of CivilEngineering Laboratory of Northern Rio de Janeiro State University (UENF).Salt Water Intrusion Meeting (SWIM) has been held since 1968. Since the firstmeeting in Hanover, Germany, as an initiative of researchers from a fewNorthern and Western European countries, the scope and number of SWIMparticipants increased steadily over the years. In the last meetings, it becamea fully international event, with participants from all over the world.In2008,after merging with Salt Water Intrusion in Coastal Aquifers (SWICA)meeting, SWIM took place for the first time outside Europe.In the present 22 ndEdition for the first time a SWIM meeting is organized in the SouthernHemisphere,having received more than 100 abstracts sent from 20 countriesof the five continents,thus confirming the growing worldwide interest in theevent.The meeting in Brazil will consist of an informal environment where studentsand those novices in the saltwater intrusion field can interact with establishedand well-known experts who are actively involved in and/ or affected by saltwater intrusion problems.Saltwater interfaces, not only in coastal areas butalso near salt deposits inland or offshore, are more and more the subject ofscientific and economic interest worldwide. Particularly in Brazil, althoughwith more than 8000 km of coast line and huge oil reserves recentlydiscovered under layers of salt (pre-salt fields), mechanisms of interaction ofgroundwater bodies with varying salinity and the geological environment arebarely known. The SWIM meeting will represent a unique opportunity to localresearchers, stakeholders and students to discuss those issues.The seven topics selected for the 22 nd SWIM were an attempt to summarizesome of the most relevant subjects concerning the study of salt waterintrusion problems in coastal aquifers. The 103 contributions submitted bySWIM participants show the importance of using different tools to study thegroundwater salinization problems. A trend observed in the 21 st SWIM inAzores is confirmed here: improved hydrogeological data, geophysical andgeochemical tools are used to develop and validate numerical models tosimulate variable density groundwater flow. Numerical model limitations andthe need to simplify their use are also recognized. This will improve themanagement tools for coastal aquifers.

During the 22 nd SWIM there will be a number of featured speakers, experts intheir fields of work, opening the main topics of the meeting. Also twooptional pre-conference short courses were kindly offered by our SWIMpartners: Schlumberger Water Services’ Visual-Modflow Course with emphasison module SEAWAT (June 12-14) and WASY's Feflow (June 15-16).We would like to thank all our colleagues and particularly our generoussponsors: Brazilian Federal Government Agencies National Research Council -CNPq and CAPES; Rio de Janeiro State Agency for Development of Science -FAPERJ; and Petrobras S.A., who agreed to contribute to this meeting and tothe publication of SWIM Proceedings book. We are also indebted to Prof. KatiaMansur, for organizing the field trip and META Agency, the SWIM Secretariat.Our special thanks to the Scientific Committee for reviewing all the papers.On behalf of the Organizing Committee, we would like to welcomeparticipants to SWIM22 in Armação do Búzios, Brazil. Your participation iscertainly the most important contribution to the meeting. We sincerely hopeyou all enjoy the 22 nd SWIM and get the best of your stay in Brazil.Gerson Cardoso da Silva Jr.Suzana Montenegro.

SUMMARYKeynote Lectures pg 13Coastal aquifer management in Europe and Ibero–AmericaCrystallisation technologies for prevention of salt water intrusion: Laboratory experimentsfor feasibility testingClimate Proof Areas: Innovative solutions for improving the freshwater availability!Modeling of historical evolution of salt water distribution on the right bank of the Scheldtin the Antwerp HarborModelling and optimization of the management systems of groundwater in the presenceof marine intrusion: the case of Salento (Apulia, Italy)Modified Eulerian - Lagrangian method for density driven flow regimeUsing Geochemical and Modeling Tools to Determine SalinityEvolution in the Aveiro Cretaceous Aquifer (Portugal)Using Groundwater Models for Coastal Management: Why Simple Modeling is BestEffects of sea level rise and climate change over salt water interfaces pg 29Assessing seawater intrusion vulnerability at a national-scale using theoretically basedvulnerability indicatorsConsiderations on the Saline Intrusion in Coastal Aquifers of Maceió Given a Possible Risein Sea LevelEffects of climate change on the freshwater lens of the German North Sea Island ofBorkumEffects of climate change to the groundwater body of the German North Sea Island of FöhrGroundwater And Biodiversity: The Singular Case of The Mangue de Pedra, Armação dosBúzios, State of Rio de Janeiro, BrazilGroundwater Salinization Risk at Recife (Brazil) due to Climatic Changes

Impact of climate change and drainage ditches on saltwater intrusion towards a coastalwell fieldProcesses controlling the presence of salty groundwater in the Red River flood plainSaltwater Intrusion and Storm Surge Processes in Coastal Areas under Climate Change: AModelling Study in Northern GermanyGeophysical methods to characterise the distribution anddynamics of saline groundwater pg 47A new downhole geophysical observatory for near-field monitoring and real-time saltwater intrusion management.Exploration of a freshwater lens 900 km away from the ocean – the Benjamín Acevalaquifer, Chaco, ParaguayJoint interpretation of geophysical borehole measurements and pumping tests forestimation of hydraulic conductivityMapping of groundwater salinization using Time Domain Electromagnetic induction in asmall coastal semi-arid aquifer in CapBon, northeastern of TunisiaMapping the fresh water body along the Dutch coast using an airborne time domainelectromagnetic survey to secure the future drinking water supplyStudy of the saltwater-freshwater interface with EM-31 and direct measurements:Implications for the freshwater discharge pattern to Ringkøbing Fjord (Denmark)Hydrogeochemical and isotopic methods to study the origin anddynamics of saline groundwater pg 69A groundwater chemistry and multi-tracer study of sources of salt water intrusion – theIsland of Falster, DenmarkDirect measurement of groundwater flow velocity near the shoreline using chemicaltracersEstimation of origin for the water salinization in different aquifers at the coastal area.Evaluation of Salinisation Processes Through Isotopic Analysis and Hydrochemistry of theAquifer Karst Salitre, State of Bahia, Brazil

Groundwater hypersalinization in a lowland coastal aquifer (Po River Plain, Italy)How to face groundwater salinization and contamination under global environmentalchange in its societal context: Challenge Of water Quality in THE Urban Environment ofRecife (Brazil)Hydrochemistry, stable isotopes and paleohydrology of the coastal aquifer near Ravenna(Italy).Hydrogeochemistry Characterization Of The Grondwater Coastal Aquifers In TamoiosDistrict / Cabofrio- RJImportance of Beach Wells Intakes for supplying reverse osmosis (RO) desalination plantsMultitracing the origin of brackish and saline groundwaters near a dune catchment areawith beach nutrition (Monster, Netherlands)Salinity Origin From Sedimentary Aquifers At Guanabara Bay Northwest – BrazilSanta Cesarea Thermal spring (South Italy)Understanding the origin of salinization of the coastal aquifer of Sousse (Tunisia) usingGeochemical and isotope investigationsManagement of aquifers with saline groundwater.Salinization prevention, control and remediation pg 107A joint pilot project of Hamburg Geological Authority and HAMBURG WATER to mitigategeogenic salt water intrusionAn injection-extraction well pair: a possible strategy to enhance groundwater withdrawalin coastal aquifersAn innovative approach for sustainable groundwater extraction in nature reservesthreatened by saltwater intrusionApplication of Eletrokinetic Barrier for Saline Water Intrusion: an approach for coastalaquifer management in Maceió-AL.How to determine a ‘reliable’ 3D fresh-brackish-saline distribution in data-rich coastalgroundwater systemsClimate Proof Fresh Groundwater Supply in The Netherlands

New approaches on modelling(general methods and solution of real cases) pg 167A hybrid FEFV reactive seawater intrusion modelBeach groundwater overheight in regional groundwater flow studiesCalibration of a density dependent model of a system for aquifer thermal energy storage,based on the measured data of a heat injection systemCoupled Hydrogeophysical Inversion for a salt water intrusion model and Time-DomainElectromagnetic (TDEM) dataDensity flow modeling with mfLab, examplesIdentification and estimation of groundwater inflow into a brackish lagoon: Fieldobservations and modeling of seasonal changes in dischargeInterrelation of brine reflux and mineral precipitation fronts in aquifers during naturalevolution of salt lakesLarge-scale drainage measures to increase freshwater availability from fossil sandy creeksModelling of Saltwater Intrusion: A New Fully Coupled Surface-Subsurface ApproachPractical solutions for the automatic calibration of the fresh-salt interface in agroundwater model using the Sea Water IntrusionPackage for MODFLOWSelected case studies pg 193Analysis of saltwater intrusion computational modeling in Recife city (Pernambuco, Brazil)Conceptual model of Dar es Salaam Quaternary coastal aquifer (DQCA) in easternTanzania and assessment of aquifer vulnerability to seawater intrusionGroundwater Indicators for Coastal Aquifer Management: The Urban Cities of Recife andMaceió, BrazilHydrogeological Study for Aquifer Management in Northern State of Rio de Janeiro -Brazil.

Hydrostratigraphic Study of Itaipuaçu District Aquifer – Maricá, RJ, Brazil.Investigation of Groundwater Salinization in the Coastal Aquifer of Recife (Brazil)Modelling the historical evolution of the fresh-salt water distribution in a Dutch-Flemishtransboundary aquiferReliable monitoring of Fresh-Saline water Interface in coastal aquifersSaline groundwater in the Quakenbrück basin verified by airborne geophysicsSalinization assessment by filed investigation and modeling of the shallow aquifer at thedownstream of Lebna watershed, TunisiaSEAWAT Model Development for Study of Saltwater Intrusion at Big Cypress Basin, FloridaThe Coastal Laboratory: salt and fresh water supplyUnderstanding of saline water hydrodynamics in aquifers(theoretical and numerical aspects) pg 217A novel approach to visualize the age stratification and internal dynamics of freshwaterlenses – laboratory experiments and numerical simulationsA precautionary note on the interpretation of coastal aquifer water level trends and waterbalancesCharacterization Of Salinity In Deep And Shallow Wells In The Municipality Of Campos DosGoytacazes/ Rj- BrazilComparison of 2D and 3D saltwater upconing under lateral flow conditions with focus onintermittent extraction; examples using data of the Amsterdam Water Supply dune area,the NetherlandsConstantly alternating upward and downward head-driven flow as mixing mechanismbetween rainwater and saline seepageGeologic effects on subsurface salinity distributions, groundwater flowpaths, and aquiferestuaryexchange in Indian River Bay, Delaware, USAGroundwater flow patterns adjacent to long-term stratified (meromictic) lake

Hydrodynamics of a coastal karst aquifer affected by saltwater intrusion under oceanicclimatic influence, Co. Clare, IrelandInfluence of the recharge in the hydraulic head evolution in the discharge zone of theMotril-Salobreña coastal aquifer (SE Spain)Mixing between fresh and salt waters at aquifer regional scale and identification oftransverse dispersivityNumerical analysis of groundwater flow system under the seabed at Horonobe coastalarea, JapanReactive pore-scale modeling of seawater-fresh water mixing interfaceSalt load to an agricultural catchment: seepage flux times concentration, or is there moreto it than that? Insights from a multi-scale tracer studySimulation Of High-Contrast Density-Driven TransportSources of salinity in the Quaternary sand aquifer of Dar-es-Salaam, TanzaniaStudy on intrusion possibility atCamboinhas coastal area The Enhanced Sea WaterIntrusion Package for MODFLOW 2005The impact of heterogeneity on seawater intrusion under pumping ConditionsThe Impact Of Hydrogeochemical Reactions On DensitiesAddendum pg 263Sources of Salinity in the Quaternary Sand Aquifer of Dar-Es-Salaam, TanzaniaAquifer Storage Recovery,the Storage Tank Method Can the Storage Tank methodincrease the recovery efficiency?Local Climate Proof Fresh Ground Water Supply: an Adaptive Water ManagementStrategy With Regional ImpactSea Water in The Telde Volcanic Aquifer, Gran Canaria Island (Spain)

Keynote Lectures

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCOASTAL AQUIFER MANAGEMENT IN EUROPE AND IBERO–AMERICAEmilio Custodioemilio.custodio@upc.eduDept. Geoengineering and Foundation International Centre for Groundwater Hydrology,Technical University of Catalonia (UPC)Gran Capità s/n, Ed. D–2, Campus Nord, 08034 Barcelona, SpainAbstract. Europe has a relatively long continental and island coastline relative to theAmericas due to geographical conditions, but in both cases important human settlements andactivities concentrate near them. This explains that coastal aquifers are often intensivelydeveloped in some areas, more often in Europe, with the result of salinity problems due toseawater intrusion, upconing of deep saline water and remnant salinity in aquitards, besidessaline water in arid areas due to climatic conditions. Often important aquifers are at risk.Some of them are relatively small but crucial for human activities, providing reserves fordroughts, and able to adapt to agriculture and tourism seasonally variable demand. In orderto prevent and to correct groundwater quality loss through salinity increase, management isneeded. Management and water governance aspects are site–dependent and need to betailored to local circumstances. Some aquifers are well–known, studied, monitored andmanaged, and may be used as a reference to devise solutions and action for other cases, if thesimilitude can be established by sound use of existing data.Keywords: Seawater intrusion, Europe, Ibero–America, water management, governance1. INTRODUCTIONIn many countries, coastal areas tend to concentrate human population, especially in theMediterranean and Atlantic coasts of Europe, but also in Ibero–America, as in Argentina,Uruguay, Brasil and Mexico, both in the Atlantic and Pacific areas. In some cases largehuman concentrations are close to large rivers that favoured early human settlements, but flowirregularity, costly water distribution to areas away from the stream and the main channels,and often poor water quality due to be downstream of other human activities, has favoured thedevelopment of coastal aquifers for human and agricultural supply. This has been the onlysolution when surface water is not available, as it is the caase of Mar del Plata, Argentina, andin most of the small islands.In many cases, aquifer development has produced well water quality degradation throughprogressive salinization, thus creating serious water supply problems. Thus, soundmanagement is needed.Saline contamination of coastal water wells is a well known process in what refers to thephysical and chemical principles. In real situations it is often highly influenced by the localarea in which the more or less thick transition from fresh water to saline water (mixing zone)develops. Thus, the heterogeneity and complexity of coastal aquifers has to be known indetail, not only to explain a given situation, but to find solutions to avoid quality problemsand to correctly manage the coastal aquifer systems.13

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA lot of research and applied work is available, often dispersed in the scientific and technicalliterature and in difficult–to–access and unpublished reports. Fortunately a few books compilepart of available knowledge (Custodio and Llamas, 1976; Custodio and Bruggeman, 1987;Falkland, 1991; FAO, 1997), and the previous 21 Saltwater Intrusion Meeting (SWIM) andthe 4 Technology of Seawater Intrusion into Coastal Aquifers (TIAC) proceedings makeavailable a huge amount of knowledge and experience. However, management andgovernance of coastal aquifers is still a subject that need development and shared experience.2. COASTAL AQUIFERS OF EUROPE AND IBERO–AMERICASummary descriptions of coastal aquifers in Europe and Spanish and Portuguese speakingAmerican countries have been presented in three papers in a recent issue of the HydrogeologyJournal (Vol. 18 no.1, 2010), and in some other works. See Karlow and Reichard (2010),Bocanegra et al. (2010), Custodio (2010a).There are some differences about coastal aquifers in these areas. The Mediterranean area is aspecial one due to the abundance of limestone and dolomite coastal formations, from thePalaeozoic up to now, which include relatively young (Miocene) reef limestones andcalcarenites. In America this also happens around the Caribbean Sea and Central AtlanticOcean, including Florida, Yucatan, Cuba, and some small islands, but with differentcharacteristics. In the Mediterranean area the low sea stand during the Quaternary glaciationsfavoured the formation of deltas containing coarse materials (Llobregat, Ter, Tet, Rhône, Po)that are key pieces for supply, and also the karstification of carbonates well below present sealevel (Calaforra, 2004; Fleury et al., 2007). A singular feature of the Mediterranean area isrelated to the Messinian crisis, during the Miocene, during which the Mediterranean sea driedout by evaporation after the Gibraltar Straight was temporarily closed by tectonic events. Thisproduced deep excavated valleys by the enhanced erosion potential. Afterwards, when theGibraltar Straights suddenly opened, these were an intense deposition of poorly permeablematerials covering previous coarse sediments in offshore areas close to the present coastline.The situation in the Atlantic coasts is similar at both sides, in which clastic sediments ongently slopping coastal platforms are common, and may form thick sandy and silty–sandaquifers in Belgium, France, Portugal, SW Spain, the Guyanas, Brasil, Uruguay andArgentina, with possible older permeable sediments at the bottom. Some large deltaicformations exist such as the Rhine–Meuse delta, that covers most of The Netherlands, butother large rivers discharge through wide estuaries with ripanian aquifers, as in the case of theSão Francisco and Paraná–La Plata rivers. Pleistocene fresh water may still exist in offshoreconfined aquifers (Edmunds and Milne, 2001; Kooi et al., 2000).Along the Atlantic coasts, coastal dune chains are quite common, as in The Netherlands,Flanders, Aveiro and Doñana in Europe, and Southern Brasil, Uruguay and Argentina. Theserecent dunes may hold locally important aquifers which are intensively developed, with a highrisk of salinization.The numerous small Mediterranean islands present very variable circumstances, from similarto those in the continent, as is the case of Mallorca and Menorca, to specific ones. Malta and14

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGozo are small carbonate islands with a freshwater lens floating on a continuous marinegroundwater body. In other small islands more complex situations exist, which include deepkarstified formation combined with active volcanism. The small volcanic islands oftencontain a low permeability core, but actual information is often poor.In the Atlantic ocean, the most important small islands are those of the MacaronesianArchipelago (Azores, Madeira, Canary and Cap Vert archipelagos), to which Fornando deNoronha island can be added (close to Brasil). They are fully volcanic and seawater problemsare limited to small –although locally important– aquifers (Custodio, 2010b). Many of themare in the arid Saharan belt, while others are quite well recharged, including among themsome Caribbean islands such as Guadelupe and Montserrat, where seawater intrusion islimited to areas close to the shore.In the Pacific Ocean, the Galapagos islands are little known form the point of view ofseawater intrusion. In Easter (Pascua) island most wells, which are close to the coast, sufferfrom some salinization due to the high permeability of recent volcanics (Herrera andCustodio, 2008).3. COASTAL AQUIFER MANAGEMENT AND GOVERNANCEThe often numerous groundwater developers of coastal aquifers, a common circumstance ingroundwater, is a serious problem for management, and especially for groundwater qualitymanagement. This is an open field of research, technology and social–economic development,in which experience is currently very limited. In Europe two well–developed managementexamples are The Netherlands –especially the area of Amsterdam– and the Llobregat deltanear Barcelona, Spain, which emulate the decades–long experience in California and to someextent in Long Island, New York. In the Llobregat case, further to decided action by the waterauthority –even with a barrier to halt seawater intrusion by injecting highly treated reclaimedwater– a groundwater users association is effective in putting together all groundwater usersto deal with existing salinity problems.Interesting management cases are that of Mar del Plata, Argentina, and nearby areas, whereabstraction is mostly for town supply, and the Hermosillo plain, Sonora, mostly for irrigation,where salinization through upconing from deep formations is a serious problem.Sound management examples are scarce. Sharing experience taking into account localcircumstances is urgently needed to preserve coastal aquifers and their important role forsupply, agriculture, the environment and the ecological services. Regulations are needed,which have to be adequate for dealing with real situations and respond to actual needs. Theapplication and management is the role of public organizations and water authorities.However, their effectiveness and the possibility of dealing with large territories and the oftennumerous groundwater developers and stakeholders highly depend on their co–operation andco–responsibility, which needs them to be organized. Experience in California is encouragingbut may be difficult to translate into the administrative and legal systems existing in many ofthe European and Ibero–American countries. So developing specific methods is a wantedgoal, as was the case of the pioneering case of the Llobregat delta (Niñerola et al., 2009).15

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesREFERENCESBarlow, P.M., Reichard, E.G., 2010. Saltwater intrusion in coastal regions of North America.Hydrogeology Journal, 18(1): 247–260.Bocanegra, E., Cardoso da Silva, G. Jr., Custodio, E., Manzano, M., Montenegro, S. 2010.State of knowledge of coastal aquifer management in South America. HydrogeologyJournal, 18(1): 261–267.Calaforra, J.M., 2004. The main karstic aquifers of southern Europe. European Commission,Directorate–General for Research, EUR 20911 (Cost Action 621), EC, Brussels, 123 pp.Custodio, E., 2010a. Coastal aquifers of Europe: an overview. Hydrogeology Journal, 18(1):269–280.Custodio, E., 2010b. Overview of saline water problems in small volcanic islands. Proc. 21Salt Water Intrusion Meeting (SWIM–21). Universidade das Açores, Ponta Delgada, SãoMiguel.Custodio, E., Llamas, M.R. 1976. Hidrología subterránea [Groundwater hydrology].Ediciones Omega. Barcelona, 2 Vols., 1–2350 [Chap. 13].Custodio, E., Bruggeman, G.A., 1987. Groundwater problems in coastal areas. Studies andReports in Hydrology, 45. UNESCO, Paris, 596 pp.Edmunds, W.M., Milne, C.J. 2001. Palaeowater in coastal europe: evolution of groundwatersince the late Pleistocene. Geological Society (London), S.P. 189: 313–327.Falkland, A. (ed.), 1991. Guide on the hydrology of small islands. Studies and Reports inHydrology no. 49. UNESCO, Paris, 435 pp.FAO, 1997. Seawater intrusion in coastal aquifers: guidelines for study, monitoring andcontrol. FAO Water Reports 11. Food and Agriculture Organization. Roma: 1–163.Fleury, P., Bakalowicz, M., de Marsily, G., 2007. Submarine springs and coastal karstaquifers: a review. J. Hydrol. 339: 79–92.Herrera, Ch., Custodio, E., 2008. Conceptual hydrogeological model of volcanic Easter Island(Chile) after chemical and isotopic surveys. Hydrogeology Journal, 16(7): 1329–1348.Kooi, H., Groen, J., Leijnse, A., 2000. Modes of sewater intrusion during transgressions.Water Resour. Res., 36(12): 3581–3589.Niñerola, J.M., Queralt, E., Custodio, E., 2009. Llobregat delta aquifer. In: Quevauviller, P.,Fouillac, A–M., Grath, J., Ward, R. (eds). Case Studies for Groundwater Assessment andMonitoring in the Light of EU Legislation. Wiley, Chichester, pp. 289–301.16

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCRYSTALLISATION TECHNOLOGIES FOR PREVENTION OF SALTWATER INTRUSION: LABORATORY EXPERIMENTS FOR FEASIBILITYTESTINGWALRAEVENS, Kristine 1 ; VANDE CASTEELE, Karel 1 ; VAN CAMP, Marc 1 ;MARTENS, Kristine 1 ; ZIEGENBALG, Gerald 2kristine.walraevens@ugent.be1. Laboratory for Applied Geology and Hydrogeology, Ghent University, Krijgslaan281-S8, 9000, Ghent, Belgium.2. IBZ-Salzchemie GmbH & Co.KG, Chemical and Geochemical Consultancy,Gewerbepark “Schwarze Kiefern”, 09633 Halsbrücke, GermanyAbstract. Salt water intrusion is a major problem in coastal areas worldwide. In many cases,salt water intrusion is the result of overexploitation of fresh water aquifers. The equilibriumbetween fresh and saline water is disturbed. Groundwater recovery leads to a pronouncedincrease in the migration of saline water into fresh water horizons. Up to now, only limitedpossibilities are given to prevent salt water intrusion. The most effective one is thedevelopment and application of water management systems allowing a sustainable use of thefresh water. The implementation of hydraulic barriers by injection of fresh or brackish wateris another strategy. Still another possibility is the construction of physical barriers. Such amethod, however, is extremely expensive with the existing technologies, such as cementgrouting or slurry wall construction, or cannot be realized due to technical problems.Grouting of fine-grained materials is more or less impossible with the existing groutmaterials. In this case, the building of the barrier typically involves the excavation of atrench, which subsequently is filled with a concrete/bentonite mixture. Injection of a solution,having comparable density and viscosity as water, with the objective of causing precipitationat some distance from the well, has only been practised in very specific cases. In theframework of the European CRYSTECHSALIN project (EC-project EVK1-CT-2000-00055), atechnology was proposed by which an oversaturated gypsum solution is injected, in order tocause grouting of the sediment. The solution is temporarily stabilized by addition of aprecipitation inhibitor; the key point is to cause the precipitation at a certain time afterinjection, when the solution has travelled a certain distance from the well. With the aim oftesting feasibility and performance of the grouting, a series of laboratory experiments havebeen executed. This paper comments on a selection of these tests, which after grouting, havebeen subjected to digital image analysis.Keywords: crystallisation technologies; gypsum barrier17

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesLOCAL CLIMATE PROOF FRESH GROUNDWATER SUPPLY: ANADAPTATION WATER MANAGEMENT STRATEGY WITH IMPACT?OUDE ESSINK, G.; DELSMAN, J.; PAUW, P.; De LOUW, P.; Van BAAREN, E.;FANECA SANCHEZ, M.gualbert.oudeessink@deltares.nlDELTARESPOBox 85467, 3508 AL Utrecht, The NetherlandsAbstract. In the Dutch coastal zone, a severe internal salinisation of the groundwater systemcan easily occur as huge volumes of brackish up to saline groundwater are already present.In addition, salt water wedges encroach the river and estuarine branches, leading to externalsalinisation of the surface water system. Both processes threaten sectors such as agriculture,drinking water supply and nature. On top, several physical drivers will jeopardize our(future) water system even more, viz. 1. the autonomous internal salinisation due to pasthydraulic head differences in the top system (e.g. high mean sea level relative to low-lyingpolder water levels), 2. climate change (including sea level rise), 3. land subsidence (up to 1m per century), and 4. operational water strategies. To make The Netherlands Climate Prooffor the coming century, fresh water supply is (next to safety against flooding) one of the toppriorities in the Delta Programme and in the Dutch National Water Plan. National adaptativestrategies are developed to make this happen. We believe that also a combination of localadaptative strategies with the focus on the groundwater system can make fresh water supplypossible on a regional scale in a future setting. The following steps towards this ClimateProof Fresh Water Supply setting can be identified: (a) better understanding the presentwater system, followed by (b) assessing the impact of future climate and anthropogenicstresses to the (ground)water system. The third step is (c) coming up with feasible, robust andflexible strategies for future water management. In this presentation, some local strategieswill be shown, illustrated with numerical models on local-regional-national scale,(innovative) monitoring campaigns (e.g. airborne geophysics) up to stakeholderparticipations. The location of the showcases is in the Dutch Southwestern Delta, a low-lyingsaline environment where climate proof fresh groundwater supply strategies have highpotentials.Keywords: salt water intrusion, climate proof, fresh water supply, modelling, climate change,water management, adaptive strategies18

H22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMODELING OF HISTORICAL EVOLUTION OF SALT WATERDISTRIBUTION ON THE RIGHT BANK OF THE SCHELDT IN THEANTWERP HARBORLEBBE, Luc 1 ; ADAMS, R. 2 ; DE DECKERE, E. 3luc.lebbe@ugent.be1. UGENT Krijgslaan 281 (S8), BE9000 Gent (Belgium)2. IMDC3. Antwerp Port AuthorityAbstract. In the framework of a study against the salinization of groundwater bodies in theharbor of Antwerp a density-dependent groundwater modeling was performed. During thenineteenth and the twentieth century the harbor expanded constantly from the city of Antwerptowards the north. This expansion took place in the polders along the Scheldt at 50 to 60 kmfrom the North Sea. Here, the Scheldt is still subject to tide and the water quality is brackish.This area is the only of the Flemish coastal plain where the depth of the fresh-salt waterinterface was not yet mapped. The present paper discusses the historic and ongoing densitydependent groundwater flow of this area and the mapping of the fresh-saltwater distributionusing both modeling and groundwater quality measurements. In order to obtain the presentday’s distribution the historical evolution of salt water distribution on the right bank wassimulated. The simulated period starts around the middle of the fourteenth century and issubdivided in five different stress periods, each defined by boundary conditions. During thefirst and longest stress period, which lasts five hundred years, the central part of the modeledarea which is now occupied by the harbor, was then occupied by the polders. In the poldersthe sediments of the phreatic aquifer were initially filled by connate brackish water. In thisarea the recharge of the groundwater reservoir was hampered by a dense network of shallowdrainage canals, causing a slow expulsion of the connate brackish water, while at the rightbank of the Scheldt, there was an infiltration of brackish water especially during the hightides. This water flows partially towards the low-lying polders developing a brackishgroundwater body under the polders along the right bank of the Scheldt. During the fourconsecutive stress period the expansion of the Antwerp harbor is schematized. During thisexpansion the docks were excavated and the surrounding terrains were raised. Due to thisraise the recharge with fresh water increased and enhanced the expulsion of connate brackishwater. The enhanced recharge on the raised terrains along the right banks of the Scheldtcauses a change in groundwater flow direction. This recharged fresh water flows in thedirection of the Scheldt and expulses the brackish water body.Keywords: historical evolution salt water distribition; interaction ground water surface water19

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMODELLING AND GROUNDWATER MANAGEMENT OF A KARSTIC COASTALAQUIFER: THE CASE OF SALENTO (APULIA, ITALY)Polemio M. 1 , Romanazzi A. 21. CNR–IRPI, Bari, Italy, m.polemio@ba.irpi.cnr.it2. Ph.D student - Università di Bari "Aldo Moro" – DISAATKeywords: Seawater intrusion, groundwater modelling, groundwater management, coastalkarstic aquifer1. INTRODUCTIONThe coastal karst aquifers are known to be highly vulnerable to anthropogenic and naturalchanges, and in particular to the overexploitation of groundwater resources. The highdegree of vulnerability is due to their intrinsic characteristics, anthropogenic pollution,and the effects seawater intrusion. The progressive population concentration in coastalareas and the increasing discharge overlapped to peculiarities of karstic coastal aquifersconstitute a huge worldwide problem, particularly relevant for coastal aquifers of theMediterranean basin. In Italy, Apulia, with its coastline extending over 800 km, is theregion with the largest coastal karst aquifers. The predominant karstic Apulian featuresmake the region extremely poor of surface water resources and rich of high qualitygroundwater resources. These resources still allow the social and economic developmentof population, improving agricultural and tourist opportunities. The continuous increasingwell discharge causes or contributes to the groundwater quality degradation, often makingthe groundwater unusable for irrigation and drinking (Polemio et al. 2009). The strategicimportance of groundwater resources and its wise management for Apulian population isdue to these risks (Cotecchia and Polemio 1998, Margiotta and Negri 2005). The aim ofthis study is to define the efficacy of existing management tools and to develop predictivescenarios to identify the best way to reconcile irrigation and drinking water demands withenduring availability of high quality groundwater. The Salento (Salentine Peninsula), wasselected being the Apulian aquifer portion exposed to the highest risk of qualitydegradation due to seawater intrusion.2. STUDY AREAApulia can be described distinguishing four main hydrogeological structures (HSs),Tavoliere, of clastic nature (Quaternary), and Gargano, Murgia, and Salento, constitutedby limestone and dolostone, which constitute a typical karstic environment (Fig. 1).Focusing on the contiguous Murgia and Salento HSs, from a geological point of view, theyconsist of almost similar Mesozoic carbonate rocks but show different hydrogeologicalcharacteristics. In particular, the Quaternary tectonic differential movement between thetwo hydrogeological structure put the Salento in condition to drain a large amount ofMurgia groundwater (Cotecchia 1979). The Salento feed coming from Murgia isdischarged through some Ionian and Adriatic coastal springs located in the northernSalento. The selected study area was the southern Salento, where the aquifer recharge isonly due to the direct rainfall infiltration. The landform is at horst and graben, where the20

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesgraben consists of Plio-Pleistocenedeposits, which are interposedbetween tabular reliefs of Mesozoiclimestone. The main aquifer, called“deep aquifer”, is constituted byMesozoic limestone. The piezometricslope is generally in the range 0.1 to2,5‰; the maximum piezometrichead is less than 4 m asl.Groundwater flow is widespreadconfined far from the coast, not onlywhere the aquifer top is below thesea level, as observed in the easternportion of study area (Cotecchia etal., 2002). Where limestone does notoutcrop, calcarenite, sands andconglomerates can constitute ashallow aquifer. In the study areacan be distinguished more shallowaquifers, each one able to exchangewater with the deep aquifer, mainly feeding this one (Calò et al. 1992).Fig.1 Geological scheme (modified after Beneduce et al. 2004). 1Fault, 2 front of the Apennines, 3 recent clastic cover (Pliocene–Pleistocene), 4 bioclastic carbonate rocks (Paleogene) andcalcarenites (Miocene), 5 carbonate platform rocks (Upper Jurassic-Cretaceous), 6 chert-carbonate rocks (Upper Jurassic- Cretaceous).Red Line – study area3. ESTIMATION OF RECHARGE RATEThe natural recharge is a critical input for planning sustainable use of groundwaterresources, therefore was defined the hydrogeological balance of the study area. The DEMwas discretized using 25-meter resolution ASTER (Advanced Spaceborne ThermalEmission and Reflection Radiometer) data. The DEM altitude ranges from 0 to 214 m asl(35 m asl as average). Rainfall and temperature monthly data of 13 gauges wereconsidered from 1925 to 1975; the period was selected to avoid the trend effect of climatechange, particularly relevant in the area from the eighties, as highlighted by Polemio andCasarano (2008). The mean annual rainfall ranges from 544 mm to 946 mm (727 mm asmean gauge value). The mean annual temperature ranges from 15.5 to 17.5 C° (meanequal to 16.6 C°). Using a multiple linear regression function of the altitude and thedistance from the Adriatic coast, the rainfall and temperature was determined in each cell,operating in a GIS environment. The monthly real evapotranspiration was determinedusing the traditional and affordable Turc method, using the modified temperatureapproach (Polemio et al. 2000). At the end, the mean annual net rainfall was calculated ineach cell: it ranges from 68 to 343 mm, 173 mm an average. The recharge or infiltrationwas calculated using an infiltration coefficient (IC) (defined as infiltration/net rainfallratio) for each hydrogeological complex, assuming values equal to 1 inside endorheicareas (Fig. 2). The mean annual recharge was equal to 150 mm.21

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives4. GROUNDWATER MODELINGThe numerical modelling was based on a "partially-physical partially conceptual"approach, with the simplifying hypothesis of an equivalent porous media. Several authorsconsider these choices the most flexible to model water flow and transport at the regionalscale in karstic areas (Andresonn and Woesser 1992, Dufrense and Drake 1999, Scanlonet al. 2003), especially for predictive management objectives (Schwarz and Smith 1988).The numerical code used was SEAWAT (Langevin et al. 2003) that combines the threedimensional groundwater flow model MODFLOW (McDonald & Harbaught 1988) withthe solute transport code MT3DMS (Zheng and Wang 1998). For the spatial discretization,Fig.2 a) Hydrogeological complexes and endorheic areas. 1) Pleistocene sands and conglomerates (IC 0.35; Kx 5*10 -6 ; Ky 5*10 -6 ;Kz 1.9*10 -8 ); 2- Upper Cretaceous limestone (IC 0.9; Kx 9*10 -4 ; Ky 9*10 -4 ; Kz 2.58*10 -2 ); 3- Andrano Calcarenite and PietraLeccese (IC 0.7; Kx 1.4*10 -5 ; Ky 1.4*10 -5 ; Kz 10 -6 ); 4- Leuca and Gravina Calcarenites (IC 0.6; Kx 1.9*10 -5 ; Ky 1.9*10 -5 ; Kz 5*10 -6 ); 5- Endorheic areas (C.I. 1); 6- drainage network; b) Mean annual recharge or infiltration map.considering the Peclet number, the study area was divided into 280-meter squared cells.12 layers and 97,2008 cells were used to pursue an accurate hydrogeologicaldiscretization. The model surface morphology was defined using DEM data. Thegeometrical 3d features and hydrogeological parameters for each hydrogeologicalcomplex were defined using published (maps from ISPRA, the national institution for theenvironmental protection and research, and PTA, the Apulian regional water protectionplan) data and unpublished, from CNR IRPI geodatabases and surveys. Inactive or noflow cells defined the internal boundary conditions, along the remaining portion of theaquifer, and the marine areas; CHB (constant head boundary-Dirichlet condition) cellswere used to shape the coastline, where the constant sea salt concentration was assigned.22

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesThe steady-state model calibration slightly modified the hydraulic conductivity, which wasformerly defined on the basis of pumping tests and literature data. Groundwater headobservations of 18 wells were compared to the simulated groundwater heads (Fig. 3).These piezometric data were acquired during the thirties, when the discharge was so lowthat quite natural flow conditions can be hypothesized (Polemio et al. 2011).5. CONCLUSIONPreliminary results ofsteady flow and ofspatial variability ofgroundwater salinityare now available.These results are thebasis for next phasesof a Ph.D. activity.The next phase willbe the validation ofthe model usingFig.3 Comparison between head observation (point) and calculated (line).additional well-headdata and sensitivity of analysis before define some simulating scenarios. This modelimproving will be the basis to simulate the space and time evolution of the seawaterintrusion phenomenon and to define tools for sustainable management of groundwaterresource.REFERENCESAndresonn M.P., Woesser W.W., (1992); Applied groundwater modelling, Academic Press,San Diego.Calò G., Gnoni R., Stani M., (1992); Caratteri idrogeologici delle falde superficiali dellaPenisola salentina e valutazione della vulnerabilità degli aquiferi, AmministrazioneProvinciale di Lecce.Cotecchia V., (1979); Survey and monitoring groundwater in salinity problems in steamsusing automatic radioisotope gauges, J. Hydrogeology, 47, UNESCO IHP Project 5.6.Cotecchia V., Polemio M., (1998); Apulian groundwater (southern Italy) salt pollutionmonitoring network, 15° SWIM, Salt Water Intrusion Meeting, Ghent (Belgium) , 25-26May.Cotecchia V., Daurù M., Limoni P.P., Mitolo D., Polemio M., (2002); La valutazione dellavulnerabilità integrata negli aquiferi: la sperimentazione nell’area campione di Coriglianonel salento. Acque sotterranee, XIX, 77, 9-20.Dufrense D.P., Drake C.W., (1999); Regional groundwater flow model costruction andwellfield site selection in a karst area, Lake City, Florida, Engineer Geology,52, 129-139Langevin C.D., Shoemaker W.B., Guo W., (2003); MODFLOW 2000: the US GeologicalSurvey modular groundwater model. Documentation of SEAWAT 2000 version with the23

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesvariable density flow process (VDF) and the integrated MT3DMS transport process(IMT), US Geol. Survey Open-File Report 03-426.Margiotta S., Negri S., (2005); Geophysical and stratigraphical research into deepgroundwater and intruding seawater in the mediterranean area (the Salento Peninsula,Italy), Natural Hazards and Earth System Sciences, 5: 127-136.McDonald M.G., Harbaugh A.W. (1988); A modular three dimensional finite differencegroundwater flow model. US Geological Survey Techniques of water resourcesinvestigations, Book 6, Chapter A1.Polemio M., Casarano D., (2008); Climate change, drought and groundwater availability insouthern Italy. In Dragoni, W., and Sukhija, B.S., eds., Climate Change andGroundwater, Volume 288: Special Publications: London, The Geological Society, p. 39-51.Polemio M., Di Cagno M., Virga R., (2000); Le acque sotterranee del Gargano: risorse idricheintegrative e di emergenza; Acque Sotterranee, 68, 41-58.Polemio M., Dragone V., Limoni P.P., (2009); Monitoring and methods to analyse thegroundwater quality degradation risk in coastal karstic aquifers (Apulia, Southern Italy),Environmental Geology. 58: 299-312.Polemio, M., Dragone, V. and Limoni P.P. (2011); La disponibilità di acque sotterranee inPuglia negli ultimi 80 anni. In: Le modificazioni climatiche e i rischi naturali, edited byM. Polemio, pp. 201-204, CNR IRPI, Bari, Italy.Scanlon B.R., Mace R.E., Barrett M. E., Smith B., (2003); Can we simulate regionalgroundwater flow in karst system using equivalent porous media? Case study BartonSprings Edwards aquifer, USA, Journal of Hydrology, 276 137-158.Schwarz F.W., Smith L.; (1988); A continuum approach for modelling mass transport infractured media. Water Resource Res., 24 (8) 1360-1372.Zheng C., Wang P.P., (1998); MT3DMS, a modular three dimensional multispecies transportmodel for simulation of advection, dispersion and chemical reactions of contaminants ingroundwater systems. Vicksburg, Mississipi Waterways Experiment Station, US ArmyCorps of Engineers.24

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMODIFIED EULERIAN - LAGRANGIAN METHOD FOR DENSITY DRIVENFLOW REGIMESOREK, Shaul; BORISOV, Vyacheslavsorek@bgu.ac.ilBEN-GURION UNIVERSITY OF THE NEGEVDepartment of Enviromental Hydrology & Microbiology; Zuckerburg Institute for WaterResearch; Blaustein Institutes for Desert Research; Ben-Gurion University of the Negev;Midreshet Ben-Gurion 84990; IsraelAbstract. We present the Modified Eulerian--Lagrangian (MEL) formulation, based on nondivergentforms of partial differential equations, for simulating transport of extensivequantities in a porous medium. Hydrodynamic derivatives are written in terms of modifiedvelocities for particles propagating phase and component quantities along their respectivepaths. The particles physically interpreted velocities also address the heterogeneity of thematrix and fluid properties. The prediction to a density driven flow problem was investigatedby four different schemes: i) Upwind Eulerian; ii) Monotone Eulerian; iii) Eulerian –Lagrangian (EL) and iv) MEL with, unlike the EL scheme, particle tracking for both the flowand transport equations. We also compared between schemes (i) and (iv) for a heterogeneousfield characterized by regular random distribution of dispersivities and hydraulicconductivity. We conclude that the MEL scheme produced the most reliable results and isbetter fitted to simulate coupled systems of balance equations.Keywords: non-divergent forms of Partial Differential Equations; Eulerian, Eulerian-Lagrangian and Modified Eulerian-Lagrangian formulation; Apparent particle velocity; FiniteDifference approximation25

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesUSING GEOCHEMICAL AND MODELING TOOLS TO DETERMINESALINITY EVOLUTION IN THE AVEIRO CRETACEOUS AQUIFER(PORTUGAL)De MELO, M. Teresa Condesso 1 ; VANDENBOHEDE, Alexander 2teresa.melo@ist.utl.pt1- CVRM – Geosystems Center. Instituto Superior Técnico. Lisbon, Portugal.2- Dept. Geology and Soil Science, Ghent UniversityAv. Rovisco Pais. 1049-011 Lisboa. PortugalAbstract. The Aveiro Cretaceous aquifer represents a main water resource of an importantindustrialized area of northwestern Portugal with a high population density and intenseagricultural and industrial activity. The growing demand for water resources in the regionled progressively to an increased reliance on groundwater from the Cretaceous aquiferformations for most of the urban and industrial water supply. Intensive pumpage since theearly sixties has gradually caused natural piezometric surface declines and is nowthreatening the natural balance of this coastal aquifer system. The aquifer has been thesubject of detailed hydrogeological and geochemical studies during the present investigation,which were complemented by the use of a variable density groundwater flow modelling usingSEAWAT. These studies contributed to derive a coherent and broad understanding of thesalinity evolution in the aquifer system since Last Glacial Maximum (LGM) and to clarifyseveral aspects related to its man. Isotopic and chloride data show that the aquifer has beenfresh for more than 18 ka. But the freshening chemical pattern of the aquifer and theevolution of pH and alkalinity suggest that the aquifer has had previously seawater and thatthere is probably still an outlet offshore which is confirmed by the flow modelling results. Thedilute nature of the Aveiro groundwaters thus indicates previous freshening of the coastalaquifer since at least the Late Pleistocene or even earlier. Higher hydraulic gradients(~0.004) during the Last Glacial Maximum (LGM) or even before LGM imposed by a sealevel lowered by approximately 130-140 m compared to present day would have acceleratedthe complete refreshing of the aquifer, with fresh water flushing the original formation water.These hydrochemical results have been validated by variable density groundwater flowmodelling using SEAWAT which indicates that the aquifer has had freshwater since LGM andthat there will be long time before salt water will be entering the aquifer from the seaboundary.Keywords: Aveiro Cretaceous aquifer, palaewaters, salinity, geochemistry, modelling26

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesUSING GROUNDWATER MODELS FOR COASTAL MANAGEMENT: WHYSIMPLE MODELING IS BESTVOSS, Clifford I.Hcvoss@usgs.govU.S. Geological Survey, Menlo Park, California, USAAbstract. Perhaps one of the strongest sources of guidance for managing aquifer systems atrisk for saltwater intrusion is parsimonious groundwater modelling analysis. ‘Parsimonious’modelling implies active avoidance of overly-complex representations when constructingmodels. A parsimonious or ‘simple’ model includes only enough features to reproduce keydata and aquifer behaviors of interest. A parsimonious modelling analysis focuses only onevaluation of model features that control answers to questions being asked about the aquifersystem. Many modeling projects have the goal of developing a model that represents themost-detailed picture of the aquifer system possible. This is neither the best use of state-of-theart modeling technology nor of the hydrologist modeler’s expertise. The model itself shouldnot be the product of a project; rather, what is learned from using models to analyze theaquifer system should be the primary product. A groundwater model is merely a tool to aidthe hydrologist in making judgements about aquifer behavior. No single simple or complexmodel is a true representation of an aquifer system, so effective model analyses must evaluatethe impact of alternative model features on questions being addressed. We never know when amodel is right, only when it is wrong. Complex models often include large amounts ofirrelevant data, resulting in increased model complexity that does not help address pertinentquestions. Often, the effort of adding complexity diverts the analysis from its true purpose andreduces the possibility that the hydrologist will deepen understanding of the aquifer system.Simple effective modelling is crucial, especially for evaluating aquifers that lack informativehydrogeologic databases, and it can be argued that most aquifers fall into this category.Success of hydrologic analysis depends much more on the hydrologist’s insight, experienceand judgment than on the elaborateness of details included in a model. Groundwater modelresults are often presented as highly-defined maps and three-dimensional images, giving theillusion of realism and certainty. When commissioning a model-development project, wellmeaningmanagers with unrealistic expectations fueled by such advertising may requestmodel-based answers that are impossible for any project to provide. For this reason, it isequally important to effective management of coastal aquifers that managers’ questions bedeveloped with an understanding of the limitations.27

Effects of sea levelrise and climate changeover salt water interfaces

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesASSESSING SEAWATER INTRUSION VULNERABILITY AT A NATIONAL-SCALE USING THEORETICALLY BASED VULNERABILITY INDICATORSWERNER, Adrian; MORGAN, L.K.; IVKOVIC, K.; CAREY, H.; SUNDARAM, B.adrian.werner@flinders.edu.auNational Centre for Groundwater Research and Training, Flinders University, AustraliaFaculty of Science and Engineering, School of the Environment, Flinders University, GPOBox 2100, Adelaide SA, Australia 5001Abstract. Assessing seawater intrusion vulnerability at a national-scale using theoreticallybased vulnerability indicators Adrian D. Werner1,2, Leanne K. Morgan1,2, Karen Ivkovic3,Hashim Carey4, Baskaran Sundaram4 1National Centre for Groundwater Research andTraining, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia; 2School of theEnvironment, Flinders University, Adelaide, Australia; 3 Naiades Geohydrology;4Geosciences Australia *Corresponding author Abstract Coastal aquifers are an importantwater resource in Australia, where 85% of the population live within 50 km of the coast.Although the threat of seawater intrusion (SWI) has been reported in all of the states and theNorthern Territory, comprehensive investigations of SWI are relatively uncommon. Toaddress this gap, a national-scale vulnerability assessment of SWI is being carried out toassess aquifers currently affected by SWI and potentially at risk as a consequence of overextraction,recharge change or sea-level rise. The project is comprised of three maincomponents: 1) Coastal Aquifer Typology; 2) Vulnerability Factor Analysis; and 3)Mathematical Analysis. Outcomes of this nation-wide project will help to prioritise areasrequiring further investigation and management of SWI. This paper discusses theMathematical Analysis component of the project. A method for first-order assessment of SWIvulnerability under both current conditions and future stresses (including sea-level rise,recharge change and reduced inflow from inland aquifers) has been developed as part of theproject, as described by Werner et al. (2012). The methodology is an extension to theanalytical sharp-interface solution of Strack (1976) and involves the use of partial derivativesto quantify rates of change in wedge toe location and seawater volume for the variousstresses. Using this method, relative vulnerability under current conditions and to differentstresses were determined for 28 case study areas identified by stakeholders as being of SWIconcern. Unconfined aquifers, confined aquifers and freshwater lens systems wereconsidered. Both application of the method and results are described. The method was foundto be consistent with the scale of the project and with the need to infer SWI vulnerability fromrelatively scant hydrogeological information and using simplified conceptual representationsof Australian coastal aquifer systems. The method has various limitations associated with theuse of analytical solutions, such as assumptions of steady-state conditions, a sharp interface,homogeneous aquifer properties and uniform hydrologic stresses. Nevertheless, the approachhas the advantage of physical and mathematical justifiability and is considered animprovement over existing relatively subjective methods for assessing SWI vulnerability overlarge scales e.g. GALDIT (Lobo-Ferreira et al., 2007). Various limitations of the method areaddressed through the other two components of the project and, as such, the MathematicalAnalysis was applied as part of a complementary approach to assessing SWI vulnerability.References Lobo-Ferreira, J.P., A.G. Chachadi, C. Diamantino, M.J. Henriques (2007)Assessing aquifer vulnerability to seawater intrusion using the GALDIT method: part 1 -31

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesapplication to the Portuguese Monte Gordo aquifer, In proceedings (ed. J.P. Lobo Ferreira,J.M.P. Viera) Water in Celtic Countries: Quantity, Quality and Climate Variability, IAHSPublication 310, International Association of Hydrological Sciences, Wallingford, pp. 161-171. Strack, O.D.L. (1976) Single-potential solution for regional interface problems incoastal aquifers, Water Resources Research 12, 1165-1174. Werner, A.D., J.D. Ward, L.K.Morgan, C.T. Simmons, N.I. Robinson, M.D. Teubner (2012) Vulnerability indicators ofseawater intrusion, Ground Water 50(1), 48-58.Keywords: seawater intrusion; vulnerablility indicators, sea-level rise32

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCONSIDERATIONS ON THE SALINE INTRUSION IN COASTALAQUIFERS OF MACEIÓ GIVEN A POSSIBLE RISE IN SEA LEVELCOSTA SOBRINHO, A.F; SILVA, A.L.C; CABRAL, J.J.S.P.; MONTENEGRO,S.M.G.L.; FREIRE, C.C.; PAIVA, A.L.R.dealrpaiva@yahoo.comUNIVERSIDADE FEDERAL DE PERNAMBUCO (UFPE);Av. Acadêmico Hélio Ramos, s/n, Cidade Universitária, Recife – PE, BrazilUNIVERSIDADE FEDERAL DE ALAGOAS (UFAL)Abstract. The issue of salinity in coastal aquifers, on the quantities of safe exploitation isincreasingly being put into evidence. Metropolitan Region of Maceio (MMR), State ofAlagoas, located in Northeastern Brazil, is not different, because in addition to increasingconcentration of population in this area, it has a large concentration of hotels and resortsthat are avid consumers of clean water and are intensely pumping the groundwater resources,which are abundant and potable. The public supply company of the State of Alagoas(CASAL), uses water pumped to increase the flow of the local chain supply and together withprivate residential condominium, extracting groundwater's through more than 400 deepwells. The aquifers in the coastal zone of the RMM are the subject of considerable concern,particularly when taking into account the rise in sea level that has been evidenced in somerecent work. Some studies of climate change estimated about one meter rise in sea levelrelative to current levels, and this would have serious consequences to these aquifers. Thealtitude in the Maceió region is normally composed of two levels; one level with altitudesbetween 0 and 5 m, and in the coastal area with above 20 m, in the region of the plateau.Thus the advance of the sea on this first level will certainly bring serious consequences to thelocal aquifers. This work has been done, through geoprocessing's estimates of recharge areasthat may possibly be attained and the consequences for the region given the rise in sea level.Keywords: sea level rise; climate change; Maceió; salinization33

Hans Sulzbacher 1 ; Helga Wiederhold 1 ; Bernhard Siemon 2 ; Michael Grinat 1 ; ThomasBurschil 1 ; Jan Igel 1 34

Helga Wiederhold 1 ; Wolfgang Scheer 2 ; Reinhard Kirsch 2 ; Thomas Burschil 1 ; MartinLilienfein 3 35

Resistivity [Ωm]0.1 1 10 100 10000 - -10 m m.s.l. -40 - -50 m m.s.l. 37

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGROUNDWATER AND BIODIVERSITY: THE SINGULAR CASE OF THEMANGUE DE PEDRA, ARMAÇÃO DOS BÚZIOS, STATE OF RIO DEJANEIRO, BRAZILMANSUR, Kátia Leite; GUEDES, Eliane; SILVA Jr., Gerson Cardoso; REBELO,Vivian de Avelar Las Casas;katia@geologia.ufrj.brCCMN – IGEO – Departamento de Geologia; Universidade Federal do Rio de JaneiroDepartamento de Geologia e Paleontologia; Museu NacionalAbstract. Mangue de Pedra (Mangue = Mangrove and Pedra = Stone) is a mangrove withspecial characteristics because it develops on rocky substract and it is about 5 kilometersaway from the river mouth. This mangrove is located in Gorda Beach, Búzios, Brazil. Thissingular situation is caused by the discharge of groundwater in the basis of palaeocliffs inthis sector of the beach. The predominant lithology is a conglomerate. These sediments weredeposited in fluvial environment, in alluvial fans controlled by the tectonic movement of thePai Vitório Fault. This fault is located in the south limit of the Barra de São João Graben. Itis a normal fault that puts side-by-side the Palaeoproterozoic orthogneiss of the basementand the Mio-pliocene conglomeratic sediments. Rubin & Almeida (2003) have mapped thefault in detail and identified 6 different units in 1:1000 scale. Those authors observed 60 mthick of fault rock filling, including a core with 3 m of breccia and ultracataclasites.Petrographic studies revealed 4 reactivation events in the rocks of Pai Vitório Fault. Oliveira(2007) has studied the mangrove of Praia Gorda. The author concluded that these plantshave good structural patterns of development. The singular aspect of this vegetation is itrocky substratum, composed by gravel, coarse sand and little blocks of rock instead of muddy/ organic sediments. The conglomerates are aquifers with medium to high favorability toexplotation of groundwater. The recharge occurs in the top of palaeocliffs and in the activecliffs and the discharge occurs in the beach. This geological position creates the bestconditions of salinity for development of mangrove over rocks and faraway of rivers. TheMangue de Pedra is a singular interaction between biodiversity and geodiversity (Mansur &Guedes, 2011).Keywords: Groundwater and Biodiversity39

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGROUNDWATER SALINIZATION RISK AT RECIFE (BRAZIL) DUE TOCLIMATIC CHANGESPAIVA, A. L. R. de; CABRAL; J. J. S. P.; MONTENEGRO, S. M. G. L.; COSTASOBRINHO, A. F.; DEMÉTRIO, J. G. A.alrpaiva@yahoo.comUNIVERSIDADE FEDERAL DE PERNAMBUCO (UFPE)Av. Acadêmico Hélio Ramos, s/n, Cidade Universitária, Recife – PE, BrazilAbstract. Recife city in Northeastern Brazil comprises a low flat land plain ( 2 to 10 metersabove mean sea level) crossed by several rivers, streams, channels and mangroves. At hightide, all these surface water elements mixed with sea water and salt concentration advancesseveral kilometers inland. Groundwater at Recife Metropolitan Region has been highlyexploited in the last three decades, the number of wells surpasses 12,000, piezometric levelsdecreased more than 50 meters at several locations and some wells present increasing saltconcentration. Several problems have been detected, such as poor technical wellconstruction, overexploitation, salinization process advances due to influence of mangroves,salinized paleochannels, old traped salt zones and salinization from rivers and streams atestuarine region. Sea level rise will increase groundwater hydraulic gradients towards land,perhaps some recharge areas will be covered and salinization risks will be much higher. Thisresearch discusses the salinization risk increase due to climatic changes and in special due tosea level rise.Keywords: sea level rise; climate change; Recife; salinization40

Per Rasmussen; Torben O. Sonnenborg; Klaus Hinsby1. INTRODUCTION41

2. METHODS Figure 1a. 42

3. RESULTS Push Reclaimed Barrier Moraine land islandsFigure 2a.43

4. DISCUSSION AND CONCLUSIONSREFERENCES -44

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesPROCESSES CONTROLLING THE PRESENCE OF SALTYGROUNDWATER IN THE RED RIVER FLOOD PLAINLARSEN, F.; PHAM, Q. N.; TRAN, V.L.; TRAN, T.L.; HOANG, H.; HINSBY, K.khi@geus.dkGEUSØ. Voldgade 10, 1350, Copenhagen, DenmarkAbstract. Radiocarbon dating of sediments in 36 sub-recent deltas worldwide has shown, thatthe sediments began to accumulate within a restricted time range, from about 8,500 to 6,500years ago (Stanley and Wide, 1994). Today, many of these deltas and their flood plainsconstitute multi-aquifer systems with saline paleowater. The Red River flood plain in Vietnammakes up such a multi-aquifer system, where saline groundwater is widespread occurring. Wehave studied the distribution of salty groundwater in this flood plain and established aconceptual model of the saltwater distribution, based on lithological information, geophysicalborehole logging and transient electromagnetic soundings. In addition, the processescontrolling the leaching of marine porewater from the sediments were analyzed with simple1D numerical modelling using SEAWAT. The investigations reveal the presence of saltypaleowaters up to 50-75 km from the coastline, and that the distribution of saltwater iscontrolled by marine deposits of the Holocene transgression. In the lower Pleistocene aquifer,the highest salinities is found below two intrinsic valleys with marine sediments. Recentintrusion of saltwater from the South Chinese Sea into shallow aquifers has been observed asfar inland as 35 km from the coastline and is probably dominated by a storm and tidegenerated transport of seawater into rivers. The observed inverted salinity profile, with highsaline water overlying fresh groundwater, is therefore a result of the presence of lowpermeable salty Holocene sediments overlying more coarse grained Pleistocene fluvialdeposits. The results of the numerical modelling show that diffusion of solids out of the lowpermeable sediment is the most important process controlling the salinity distribution, whenthe sediment hydraulic conductivity is lower than 10-7 m/s. This process is slow, even in ageological time perspective, and explains why salinity concentrations up to 10-15 % that ofseawater is still present in sediments far inland. In contrast, density driven transport of saltsin the more high permeable sediments is a relatively fast process, which can flush the marineporewater out of the sediments within few tens or hundreds of years. The saltwaterdistribution in the Red River delta plain has many similarities with other reportedoccurrences of saltwater controlled by the global eustatic sea-level changes during the past8,000 – 9,000 years.Keywords: Holocene transgression, SEAWAT, hydrogeophysics45

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSALTWATER INTRUSION AND STORM SURGE PROCESSES IN COASTALAREAS UNDER CLIMATE CHANGE: A MODELLING STUDY INNORTHERN GERMANYHEROLD, Maria; YANG, J.; GRAF, T.; PTAK, T.mherold@gwdg.deUNIVERSITY OF GOETTINGENApplied Geology, Geosciences Center, University of Göttingen, Goldschmidtstr. 3, 37077Göttingen, GermanyAbstract. Climate change will affect coastal groundwater resources due to a rising sea leveland an increase in storm intensity and frequency. Increasing saltwater intrusion into thegroundwater zone as well as the intrusion of dense water, supplied by overtopping waves, intothe subsurface through the unsaturated zone can be expected. Using Hydrogeosphere, thesescenarios are investigated here in a two-dimensional cross-sectional surface-subsurfacemodel of a region at the North-German coast that is heavily influenced by anthropogenicactivities, and where groundwater resources are essential for future generations. It wasnecessary to develop a new approach to model variable density and variably saturated flowand transport for this coupled surface-subsurface system. We investigated the effect of tidalfluctuations on the pressure head and on the concentration of seawater in the subsurface. Theresults show that pressure head is affected only in areas where hydraulic conductivity is highand that an impact on concentration of seawater is relevant only within a very localised zoneclose to the sea. We found additionally that an increase in sea level by 60 cm causes thesaltwater wedge to intrude up to 160 m further into the subsurface. The simulation ofovertopping waves which lead to the formation of a pond behind the dyke showed that theinfiltration depth of this water as well as the saltwater concentration which could reachpotential drinking water wells is highly dependent on the hydraulic conductivity of thesubsurface. The results highlight the potential impacts and the importance of climate changerelated future stresses with respect to groundwater supply in coastal areas and the necessityto model coastal systems in an integrated coupled approach.Keywords: saltwater intrusion modelling; climate change; overtopping waves; tidal influence46

Geophysical methods tocharacterise the distribution anddynamics of saline groundwater

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA NEW DOWNHOLE GEOPHYSICAL OBSERVATORY FOR NEAR-FIELDMONITORING AND REAL-TIME SALT WATER INTRUSIONMANAGEMENTPEZARD, Philippe A.; PERROUD, H.; ROUSSET, D.; DENCHIK, N.; GAUTIER, S.;LOFI, J.; HENRY, G.; BARRY, S.; BELLOT, J.-P.; NEYENS, D.ppezard@gulliver.frCNRS - GEOSCIENCES MONTPELLIER16 rue Jacques Coeur - 34000 Montpellier - FranceAbstract. A new downhole geophysical observatory for near-field monitoring and real-timesalt water intrusion management. Philippe A. Pezard1,3 (ppezard@gulliver.fr), HervéPerroud1, 2, Dominique Rousset2, Nataliya Denchik1, Stéphanie Gautier1, Johanna Lofi1,Gilles Henry1,3, Simon Barry3, Jean-Philippe Bellot3, and Denis Neyens3. 1GéosciencesMontpellier, CNRS, université de Montpellier 2, 34000 Montpellier, France 2Université dePau et des Pays de l'Adour (UPPA), 64000 Pau, France, 3imaGeau, Cap Alpha, 34830Clapiers, France Initially as part of the EC-funded ALIANCE project (FP5; 2002-2005), anew type of near-field, high frequency downhole hydrogeophysical observatory was designed,constructed and set-up along the Mediterranean at different coastal sites (Montpellier,Roussillon, Hyères, in France; Mallorca in Spain) in terms of geological context,hydrological regime and local human impact. The new downhole method is conceived forlong-term in-situ monitoring to prevent brine intrusion in coastal aquifers. The principle ofthe observatory is based on high-frequency (such as daily) probing of the formation electricalresistivity around a borehole over periods of several years. For “real-time” subsurfacemanagement, this device is aimed at producing accurate near-field boundary conditions toreduce uncertainties in models, and thereby contribute to the decision-making process forendangered aquifer management. Increasedly, this new system is being applied not only torisk management in the context of salt water intrusion in coastal aquifers, but also forlanslide monitoring control or else for the depollution of petrochemical industrial sites.Keywords: Autonomous high-frequency downhole electrical observatory - In-situ salt waterintrusion monitoring and management49

EXPLORATION OF A FRESHWATER LENS 900 KM AWAY FROM THE OCEAN -THE BENJAMÍN ACEVAL AQUIFER, CHACO, PARAGUAYINTRODUCTION 50

METHODS 51

RESULTS52

DISCUSSION AND CONCLUSIONS ACKNOWLEDGEMENTS53

REFERENCES54

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesJOINT INTERPRETATION OF GEOPHYSICAL BOREHOLEMEASUREMENTS AND PUMPING TESTS FOR ESTIMATION OFHYDRAULIC CONDUCTIVITYCLAUS, J. 1 ; LEBBE, L. 1 ; HINSBY, K. 2luc.lebbe@ugent.be1. UGENT2. GEUSkrijgslaan 281 (S8) BE9000 GentAbstract. A joint interpretation of geophysical borehole measurements and pumping tests isapplied in order to approximate hydraulic parameters ofquaternary sediments in the Flemishcoastal plain.This studyis performed in the framework of CLIWAT, a transnational projectabout climate change and coastal groundwater in the North Sea Region. By modifying knownrelations between the hydraulic conductivity and borehole measurements (natural gammaradiation andelectrical conductivity), a new method was developed to estimate more detailedvariations in hydraulic conductivity than can be obtained from pumping tests. From theassumption that the natural gamma ray and the electrical conductivity bothdepend on thespecific surface of sediments, a relationship between the two was established. By insertingthis relationship intoRepsolds formula (Repsold, 1989), an estimation of the hydraulicconductivity can be made. We optimize this adjusted Repsold formula, which wasoriginallydeveloped for a research site atGorleben(Germany),for application at our researchsitelocated on the Belgian coastal plain. Fieldwork was conducted in the quaternary of twotest sites in the polder area near Ostend. On each site a double pumping testandGeophysicalborehole measurements of natural gamma radiation and electrical conductivitywereperformed. The software package HYPARIDEN (Lebbe, 1999) was used to retrieve theoptimal hydraulic parameter valuesfromthe pumping test data. An initial estimate ofparameters is required to run this inverse model. In a first step the adjusted formula ofRepsold was applied to retrieve these initial values. The parameters resulting from runningthisfirst model were then compared with the initial approximated values and an adaption tothe adjusted Repsold formula was made accordingly. By following this procedure iteratively,one can find a formula fully optimized for estimation of hydraulic conductivities based on thegeophysical borehole measurements. This formula can then be used for initial estimation ofthe parameters as inputto the HYPARIDEN model. The main advantage of this formula is thatit provides a way to estimate a variation in the initial hydraulic conductivities based onphysical measurements, where otherwise a variation needed to be estimated based on ownexperience. The developedprocedure can be applied to optimize this adjusted Repsold formulafor other regions.Keywords: parameter estimation; geophysical borehole measurements; multiple pumpingtests55

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmMAPPING OF GROUNDWATER SALINIZATION USING TIME DOMAINELECTROMAGNETIC INDUCTION IN A SMALL COASTAL SEMI-ARID AQUIFERIN CAPBON, NORTHEASTERN OF TUNISIAChekirbane Anis 1 ; Maki Tsujimura 1 ; Atsushi Kawachi 1 ; Hiroko Isoda 1 ; TarhouniJamila 2 ; Wataru Yamada 1 ; Mizuho Takahashi 1 ; Amri Faouzi 3anischkirbene@gmail.com1 - University of Tsukuba, Japan; 2 - National Institute of Agronomy (INAT), Tunisia;3 - Ministry of Agriculture and Water Resources, TunisiaUniversity of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 JapanAbstract. The study area is a small coastal plain drained by an ephemeral stream networksubject of several pollutant discharges such as oilfield brine coming from a neighboring oilcompany and wastewater from Somaa city located in the upstream of the plain. Furthermore,a hydraulic depression of more than -5 m a.s.l is observed near the coastal part of the aquifer.Associated with high salinity of groundwater, it is the proof of seawater intrusion. TimeDomain Electromagnetic method (TDEM) based on 28 soundings was conducted in Wadi AlAyn plain to delineate the saline groundwater. Basing on longitudinal and transversalresistivity 2D-pseudosections calibrated with observed boring data, resistivity values lesssaltwater plume. Measured electrical conductivity of groundwaterwas also used for calibration. In the upstream part of the plain, the saltwater plume is due tothe infiltration of oilfield brine through the sandy bed of Wadi Al Ayn. It is longitudinallyfound in depths reaching -75 m. However, in the coastal part of the aquifer, groundwatersalinization is due to seawater intrusion and the salty water is located between 30 – 60 mdepth and has an inland extent around 2 km from the shore line.Keywords: Wadi Al Ayn plain, saline intrusion, TDEM, resistivity sounding56

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mm1. INTRODUCTIONSince the 2000s, a sudden change of groundwater salinity was registered in the wellsexploiting the shallow aquifer at Wadi Al Ayn plain in CapBon and was reported andcomplained by local farmers. However, groundwater salinization origin and processes arestill poorly understood. This study aims to investigate the spatial extent of the saline plumecontaminating the groundwater in Wadi Al Ayn plain, CapBon, northeastern of Tunisia,basing on Time Domain Electromagnetic investigation. The study area is the plain of Wadi AlAyn, a small coastal semi-arid floodplain located in CapBon peninsula, northeastern ofTunisia (Fig.1). The study area is located in the vicinity of an oilfield exploited since 1994.Oil production is accompanied by water with high salinity called oilfield brine. Since thebeginning of exploitation in Zinnia oilfield company in 1994 until its end in late 2009, theseparated brine from oil are directly rejected in the sandy bed of Wadi Al Ayn without anytreatment. In Al Ayn plain, the Quaternary sediments and the top layers of the Upper Mioceneare hosting a significant shallow aquifer used principally for irrigation and drinking purposes(Ben Salem, 1992).2. METHODOLOGYFig.1: Geological map of the study areaThe TDEM system used in the survey consisted of square transmitter (Tx) loop (50 m by 50 m)and a medium air coil receiver (Rx) antenna located inside the loop, commonly known as acentral loop array (McNeill, 1994). The current driven through the transmitter loop creates aprimary magnetic field. During the rapid current turnoff, this primary magnetic field is timevariantand in accordance with Faraday’s Law; an electromagnetic induction is produced,which in turn results in eddy current flow in the subsurface. The intensity of these currents at57

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmcertain time and depth depends on ground resistivity (Kaufman and Keller, 1983; Mills et al.,1988). Depth of investigation depends on the time interval after shutoff of the primary current(Goldman et al., 1991; McNeil, 1994). A smooth-model TEM inversion program namelySTEMINV was used for 1-D modeling and the inversion of measured TDEM data into verticalresistivity stratification.3. RESULTS AND DISCUSSIONThe pseudosection of vertical resistivity variation (Fig.2) shows high resistivity values in theupstream area ethe unsaturated zone and fresh water saturated sandstone and gravel in the aquifer.Fig.2: Pseudo-2D resistivity profile obtained from TDEM measurementsLow resistivity vacoastal part of Daroufa plain at depth ranging from 10 to 75 m for the former and from 45 to75 for the latter. Basing on the boring data of the wells 10698/2 and 10904/2 the geologicalcalibration was performed and different aquifer lithologies were differentiated. The resistivity) is depending from the electrical conductivity (EC of pore waterIn thestudy area, a significant power relationship was found between EC and: -0.56(R 2 = 0.7). Thus, it is possible to transform the vertical resistivity variation to an EC profile.The highest EC values are located beneath the middle part of Wadi Al Ayn, where theyrepresent the saline plume coming from the previously infiltrated oilfield brine through thesandy bed of the wadi. In addition, high EC values are found in the coastal part of Daroufaplain where they reflect a possible seawater intrusion. According to Rhoades, 1982 a water isconsidered highly saline when its EC is ranging from 10 to 25 mS/cm. Therefore, followingthis scale, an exact delineation of the saline water plume was mapped (Fig.3).58

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmFig.3: Geological cross-section and delineation of saline water plumes in Wadi Al Ayn plainCONCLUSIONThe use of TDEM soundings provided reliable results for identifying the subsurface geologyand delineating the saline water plume in Wadi Al Ayn and Daroufa plains. The infiltratedoilfield brine through the sandy bed of Wadi Al Ayn reached depths of 75 m and has alongitudinal extension of 1500 m beneath the Wadi. In Daroufa area, the main source ofgroundwater salinization is seawater intrusion; the interface between saltwater andfreshwater reached 2 km from the coast to inland and it is found in depths between 30 and 60m.REFERENCESBen Salem, H., 1992. Contribution a la connaissance de la geologie du CapBon: stratigraphie,tectonique et sedimentologie. Doctoral thesis. Faculty of sciences, Tunis. 203p.Goldman, M., Gilad, D., Ronen, A. & Melloul, A., 1991. Mapping of seawater intrusion intothe coastal aquifer of Israel by the time domain electromagnetic method. Geoexploration28, pp. 153 – 174.Kaufman, A.A. & Keller, G.V., 1983. Frequency and transient soundings. Elsevier,Amsterdam, 685 p.McNeil, J.D., 1994. Principles and application of time domain electromagnetic techniques forresistivity sounding. Geonics Ltd. Technical note TN 27.Rhoades, J.D. 1992. Instrumental field methods of salinity appraisal, pp. 231- 248, inAdvances in measurement of soil physical properties: Bring theory into practice. G.C.Topp, W.D. Reynolds, and R.E. Green (Eds.).59

MAPPING THE FRESH WATER BODY ALONG THE DUTCH COAST USING ANAIRBORNE TIME DOMAIN ELECTROMAGNETIC SURVEY TO SECUREFUTURE DRINKING WATER SUPPLY - INSIGHTS IN HYDROGEOLOGICALTREASURES AND PUZZLES 1. INTRODUCTION60

2. RESULTS, HOW TO GET THERE AND WHERE TO GO FROM THERE?61

2.1 Processing data to information62

STUDY OF THE SALTWATER-FRESHWATER INTERFACE WITH EM-31 ANDDIRECT MEASUREMENTS: IMPLICATIONS FOR THE FRESHWATERDISCHARGE PATTERN TO RINGKØBING FJORD (DENMARK) Keywords:1. INTRODUCTION64

2. METHODOLOGY 3. RESULTS65

4. DISCUSSION5. CONCLUSIONS67

ACKNOWLEDGMENTSREFERENCES68

Hydrogeochemical and isotopicmethods to study the origin anddynamics of saline groundwater

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA GROUNDWATER CHEMISTRY AND MULTI-TRACER STUDY OFSOURCES OF SALT WATER INTRUSION – THE ISLAND OF FALSTER,DENMARKHINSBY, K.; JESSEN, S; LARSEN, F.; POSTMA, D.khi@geus.dkGEUSØ. Voldgade 10 1350, CopenhagenAbstract. Groundwater abstraction in coastal regions is challenged by the projected sea levelrise, which will result in a landward migration of marine waters in coastal aquifers andincrease the risk of sea water intrusion to water supply wells in many hydrogeologic settings.In some cases, however, other sources of groundwater salinity than modern sea waterintrusion exist, such as leakage of connate sea water from shallow Holocene marine depositsand saltwater upconing, or upwards diffusion controlled salinity flux due to fossil sea waterin deep deposits. A sound understanding of the relative importance of these sources isimperative for a proper planning and management of water abstraction in coastal regions.We studied the distribution and sources of groundwater salinity in a 30 km2 area on theIsland of Falster, Denmark. Part of the area was a brackish lagoon until mid-1800, whenland reclamation was initiated by drainage canals and pumping. Around 1900 a 17 m longdike was constructed towards the Baltic Sea (salinity ~1.1 %) to protect against flooding.Groundwater abstraction takes place from a dual-porosity Cretaceous chalk aquifer, which issemi-confined primarily by Quaternary glacial tills and Holocene (estuarine-marine)deposits. Airborne and borehole geophysics were conducted in the area, and the groundwaterchemistry and environmental multi-tracer (3H/3He, 4He, 18O, 2H, 14C, 13C, 87Sr/86Sr)composition of 10 water supply wells and five monitoring wells were investigated. Theinterface between freshwater of drinking water quality and oceanic saltwater of the formerCretaceous sea is relatively wide (~100 m) and found to be controlled mainly by diffusion.The chloride concentration breach the WHO drinking water guideline of 250 mg/L in somewater supply wells, which all abstract water from the chalk at a depth of about 18-20 m belowsurface (~18-20 m below sea level). The combined tracer data is used to identify the relativeimportance of the three sources of chloride: i) modern (present-day) sea water intrusion, ii)leakage of saline water from shallow Holocene marine sediments, and iii) upconing orupwards (diffusive) flux of the chalk fossil saline water. Drainage canals in the reclaimedarea and drainage pumping have been found to have a significant effect on the salinitydistribution in the aquifer system (see abstract by Rasmussen P. et al. on climate changeimpact modeling in the same study area).Keywords: hydrochemistry, isotopes, tracers71

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesDIRECT MEASUREMENT OF GROUNDWATER FLOW VELOCITY NEARTHE SHORELINE USING CHEMICAL TRACERSYECHIELI, Yoseph; LUTZKI, H.; MAGAL, E.; WEINSTEIN, Y.yechieli@gsi.gov.ilGEOLOGICAL SURVEY OF ISRAEL30 Malkhei Israel StreetAbstract. Groundwater abstraction in coastal regions is challenged by the projected sea levelrise, which will result in a landward migration of marine waters in coastal aquifers andincrease the risk of sea water intrusion to water supply wells in many hydrogeologic settings.In some cases, however, other sources of groundwater salinity than modern sea waterintrusion exist, such as leakage of connate sea water from shallow Holocene marine depositsand saltwater upconing, or upwards diffusion controlled salinity flux due to fossil sea waterin deep deposits. A sound understanding of the relative importance of these sources isimperative for a proper planning and management of water abstraction in coastal regions.We studied the distribution and sources of groundwater salinity in a 30 km2 area on theIsland of Falster, Denmark. Part of the area was a brackish lagoon until mid-1800, whenland reclamation was initiated by drainage canals and pumping. Around 1900 a 17 m longdike was constructed towards the Baltic Sea (salinity ~1.1 %) to protect against flooding.Groundwater abstraction takes place from a dual-porosity Cretaceous chalk aquifer, which issemi-confined primarily by Quaternary glacial tills and Holocene (estuarine-marine)deposits. Airborne and borehole geophysics were conducted in the area, and the groundwaterchemistry and environmental multi-tracer (3H/3He, 4He, 18O, 2H, 14C, 13C, 87Sr/86Sr)composition of 10 water supply wells and five monitoring wells were investigated. Theinterface between freshwater of drinking water quality and oceanic saltwater of the formerCretaceous sea is relatively wide (~100 m) and found to be controlled mainly by diffusion.The chloride concentration breach the WHO drinking water guideline of 250 mg/L in somewater supply wells, which all abstract water from the chalk at a depth of about 18-20 m belowsurface (~18-20 m below sea level). The combined tracer data is used to identify the relativeimportance of the three sources of chloride: i) modern (present-day) sea water intrusion, ii)leakage of saline water from shallow Holocene marine sediments, and iii) upconing orupwards (diffusive) flux of the chalk fossil saline water. Drainage canals in the reclaimedarea and drainage pumping have been found to have a significant effect on the salinitydistribution in the aquifer system (see abstract by Rasmussen P. et al. on climate changeimpact modeling in the same study area).Keywords: tracers, groundwater velocity72

ESTIMATION OF ORIGIN FOR THE WATER SALINIZATION IN DIFFERENTAQUIFERS AT THE COASTAL AREA.Keywords:73

Figure 1 Location map of study area.and Yuchi Formation by the present rainwater was limited in the central part of marsh.Groundwater was considered to be recharged at the eastern hilly area or at the western sanddune.METHODSCore samples were obtained from three boreholes in the drilling site (No.1:158-1004m, No. 2:30-100m, No. 3: 100-160m). Surface of cores were removed to get rid of fluid from the freshcore and sealed in vacuumed package. For all drillings, a 30 mg ± 10% of Amino G acid wasused as the tracer to check the influence of drilling fluid to the pore water in collected coresamples.In the laboratory, the pore water samples were extracted by centrifugation and squeezingmethods. If the pore water contained more than 10% of fluid tracer, additional chemicalanalyses were omitted. In 18 O)were measured by ion chromatography (Dionex IC25) and gas analyzer (Picaro L2120-I),respectively.RESULTS AND DISCUSSIONVertical profile of Cl - concentration and 2. Inthis figure, Cl - concentration in the alluvium reached approximately 900mg/l around the 40mbgs, and then decreased with the increase of depth. Similar trend was reported by HRISE(2007). They had a 100m deep observation well close to our drilling site, and also measuredpore water chemistry up to 100m. Their vertical Cl - concentration data overlapping our data isshown in Figure 3. In this figure, highest Cl - concentration value was identified in lagoondeposit. also became small with the increase of depth in the alluvium, same as thetrend of Cl - concentration. Figure 4 shows the 18 O in pore waterand groundwater samples. Isotopic value of shallow groundwater collected from the well(HDW) with a screen of 5.5-21.4m, were plotted on local meteoric water line, suggesting thatthis groundwater was recharged by the present rainwater. However, isotopic values of pore74

water were plotted below the line, and showed smallest value at 100m bgs. The groundwatercollected from observation well (DD-2, screen depth: 90-100m) was also plotted on a same-diagram. It was indicated that these pore water and groundwater wererecharged by palaeo-rainwater at the last glacial age. Therefore, groundwater in the alluviumhad different origin with a silty lagoon deposit boundary, and high Cl - concentration in porewater collected around 30m bgs was due to washout from marine sediment. Below thealluvium, Cl - and water recharged by palaeo-rainwater was confirmed by the geophysical explosion (Figure 5).Furthermore, the result of geophysical explosion indicated that fresh water existed under theseabed. From 300-470m bgs, Cl - concentration increased gradually and decreased again up to also shifted to a slightly high value in this zone. Based on the numericalanalysis, a remarkable increase of Cl - and by the diffusion. Vertical profile of Br/Cl ratio also supported this suggestion, because theratio was constant below the depth of 500m bgs (Figure 2). Furthermore, Br/Cl ratio of porewater was higher than that of seawater in this figure, indicating that Br - has some origin otherthan seawater. Existence of groundwater with high Br/Cl ratio has been found in the world oiland gas field. It was reported that high Br concentration in these groundwater originated withthe degradation of organic matter in marine sediment and Br ion had a positive correlation toNH 4 + ion (Maekawa et al., 2006). Positive correlation between both ions was identified in ourstudy.75

Therefore, it was clarified that the brine below the depth of 800m bgs was palaep-seawater.CONCLUDING REMARKSExistence of five hydrological zones with different origin was identified from the verticalprofile of Cl - and existed up to 300m bgs and was storedunder the seabed. The fresh-groundwater recharged by present-rainwater existed only in upperpart of alluvium. Water salinization in deep aquifer was caused by the diffusion processbetween palaeo-fresh water and palaeo-seawater. Verification between groundwater age andgeological age is necessary in the future.REFERENCESHathaway, J.C., W.P.P.C. Valentine, R.E. Miller, D.M. Schultz, & F.T. Manheim, 1979. U. S. Geological SurveyCore Drilling on the Atlantic Shelf. Science, 206 (4418), pp515-527HRISE, 2007. Heisei17year. Annual working papers, pp258. (in Japanese)Maekawa, T., Igari, S & Kaneko, N. 2006. Chemical and isotopic compositions of brines fromdissolved-in-water type natural gas fields in Chiba,Japan. Geochemical Journal, 40. 475-484.76

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesEVALUATION OF SALINISATION PROCESSES THROUGH ISOTOPICANALYSIS AND HYDROCHEMISTRY OF THE AQUIFER KARST SALITRE, THESTATE OF BAHIA, BRAZILTereza Cristina Bittencourt Nossa 1 ; Luiz Rogério Bastos Leal 2 & Maria do Rosário Zucchi 3& Antônio Expedito Gomes de Azevedo 41Htereza.nossa@cprm.gov.brH - 1 Serviço Geológico do Brasil (CPRM);2,3,4 Universidade Federal da Bahia (UFBA) .1 Av. Ulysses Guimarães, 2862, CAB. CEP: 41.213-000. Salvador-BA. Brasil.Abstract - The study area is located in the microregion of Irecê, located in the north centralpart of Bahia state, including a pilot area of the karst aquifer Salitre, defined in themunicipalities of Irecê and Lapão, part of the hydrogeological basin of the Green river andAlligator river. It makes up a total area of approximately 250km², consisting ofNeoproterozoic carbonate rocks of the Salitre Formation. This geological unit is the karstaquifer Salitre, which is the main source of water for irrigation purposes. A risk assessmentof salinization and sodification was carried out by a study of groundwater quality used forirrigation, with analysis of 40 physical-chemical parameters and isotope characterizationthrough deuterium, excess of deuterium, oxygen-18 and dissolved inorganic carbon (D, d, 18 O, 13 C CID ) in water samples collected from wells in the Salitre aquifer. Samples collectedin the eastern sector of the area, upstream, have a lower isotopic enrichment than thoseobtained from wells located in the area north-northwest, downstream flow, which showedhigher isotopic oxygen-18 ( 18 O) and deuterium (D) values, demonstrating that more wateris evaporated and subjected to interactions with the limestone throughout time. Theincreasing values of dissolved inorganic carbon ( 13 C CID ) highlight the fact that the isotopicenrichment occurs preferentially in the E-W direction, consistent with preferential flowdirections obtained in the area. The analyses of the water used for irrigation purposesshowed that in both periods of 89% of water samples are brackish and 11% saline. Coupledwith this, 89% of the groundwater analyzed were classified as C 3 S 1 , can normally be used forirrigation and only 11% of the samples were classified as C 4 S 1 , which are water should not beused for irrigation according to the danger salinization of soils.Keywords: hydrochemistry, isotopic analysis, water quality for irrigation, karst aquifer.77

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONThe implementation of programs for groundwater monitoring helps in improving theirplanning, protection and management.The karst regions, such as micro-region of Irecê usually are areas of great economic interestand hydrogeological because, in most cases, although having a low density of surfacedrainage, have valuable water reserves in the subsoil (Bastos Leal & Silva , 2004). Fertilesoils and rugged topography of this region favor some agricultural activities, which is themain economic activity, and groundwater is heavily used for irrigation purposes, due tolimited availability of surface water.The research area is formed by a polygon comprising the municipalities of Irecê and Lapão,the state of Bahia, with an area of approximately 250km² (Nossa, 2011).2. MATERIALS AND METHODSNossa (2011) analyzed a total of 72 parameters used to diagnose hydrochemical and isotopicarea, defined based on Ordinance 518/2004 of the Ministry of Health, which sets maximumlimits for drinking water standards for human consumption, and Resolution CONAMA396/2008 establishing these values for several purposes than human consumption, such aswatering livestock, irrigation and recreation. The collection periods were selected based ondata obtained from the rainfall recorded at the Station Irecê (Figure 1).2.1. Physical-chemical analysisThe physical and chemical analyzes were performed at the Laboratory of Mineral Waters ofthe CPRM (LAMIN), based on SMEWW (Clesceri, et al., 1998), considering the cations:aluminum, antimony, arsenic. barium, beryllium, boron, cadmium, calcium, lead, cobalt,copper, chromium, tin, strontium, iron, lithium, magnesium, manganese, molybdenum, nickel,potassium, selenium, silicon, sodium, titanium, vanadium and zinc in addition to the anions:bromide, chloride, fluoride, phosphate, nitrate, nitrite, and sulfate. Were selected for analysisalso carbonate and bicarbonate, carbonate according to the lithology of the area and theparameters total hardness, electrical conductivity, total dissolved solids and pH, a total of 40physical and chemical parameters.2.2. Isotopic analysisThe methods used for collection and storage of samples for analysis of oxygen-18, deuterium,deuterium excess and dissolved inorganic carbon ( 18 O, D, d, 13 C CID ) were determinedaccording to the instructions of the International Atomic Energy Agency (IAEA, 2002) andanalyzes were performed at the Laboratory of Applied Nuclear Physics, Federal University ofBahia (LFNA-CPGG/IF-UFBA).78

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives3. RESULTS AND DISCUSSIONOut of 40 parameters analyzed in the laboratory, the variables which presented values abovethe limits of the maximum values allowed by Ordinance 518/2004 of the Ministry of Healthand by CONAMA Resolution 396/2008 were: calcium (100.00%), total hardness (75.06%),magnesium (69.00%), total dissolved solids (22.24%), sulfate (5.56%) and fluoride (5.56%)portray the natural conditions of the karst aquifer Salitre occurring throughout the area, inaddition to nitrate (83.4%) and nitrite (2.78%) may arise naturally from the excess of organicmatter in the environment or anthropogenic due to contamination caused by inadequatesanitation or, depending on the intensive use of nitrogen fertilizers. The detection chloride(16.68%) can be associated with deficiency in the circulation water or groundwater scatteredfoci of infection. The occurrence of arsenic (8.33%), present in a timely manner ingroundwater, may be related to inappropriate use of pesticides on crops in the area.The analysis of Piper diagrams (Figure 2) shows that 51.62% of the analyzed samples arecharacterized as water Calcic Bicarbonated and Mixed and 48.38% have features of Calcicand Mixed Chlorinated water.The stable isotope analyzes (Figure 3) showed evidence that the origin of salinization of theaquifer Salitre, may be either related to its interaction with the carbonate sequence featuringFormation Salitre, as with evaporation processes, and may have contribution alsotranspiration by plants. This can be diagnosed on the results of groundwater samples collectedfrom wells located in the eastern sector of the area, the amount of flow that have a lowerisotopic enrichment than those obtained from wells located in the area north-northwest,downstream of the flow, with isotopic values higher oxygen-18 ( 18 O) and deuterium (D),demonstrating that more water is evaporated and subjected to interactions with the limestoneby an interval of time. What can be seen by the increasing values of dissolved inorganiccarbon ( 13 C CID ), which highlights the fact that the isotopic enrichment occurs preferentiallyin the direction (E-W), consistent with preferential flow directions obtained in the area.The analysis of the water used for irrigation purposes showed that 88.88% of water samplesare brackish and 11.12% are saline solution. Coupled with this, 89% of the groundwateranalyzed were classified as C 3 S 1 , can normally be used for irrigation and only 11% wereclassified as C 4 S 1 , which are water should not be used for irrigation according to the danger ofsoil salinity (Figure 4).79

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives16014020092010Precipitaçao (mm)120100806040200JAN FEV MAR ABR MAI JUN JUL AGO SET OUT NOV DEZMêsFigure 1: Index rainfall recorded at Station Irecê(period 2009-2010).Figure 2: Piper Diagram showing the chemicalbehavior of water wells collected during 2010.C 13 (‰ )0-5-10-15JUN/JUL 2010d (‰ )D (‰ )O 18 (‰ )1050-10-20-300-2-4-6LA-02LA-04LA-06LA-08LA-10LA-12LA-14IR-16IR-18IR-20IR-22IR-24IR-26IR-28IR-30IR-32IR-34IR-36Figure 3: Analysis of oxygen-18 isotope,deuterium, deuterium excess and dissolvedinorganic carbon ( 18 O,D, d, 13 C CID ).Figure 4: Lemoine Diagram showing thebehavior of groundwater for agriculturalpurposes.80

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives4. REFERENCESBastos Leal, L. R., Silva, H. P. da. (Org.). 2004. Modelização da dinâmica hidrológica einstrumentos para a gestão do sistema aquífero-rio das bacias hidrográficas dos rios Verde eJacaré - região semi-árida do estado da Bahia. Relatório técnico final do convênio decooperação técnico-científica celebrado entre a Superintendência de Recursos Hídricos doEstado da Bahia e a Universidade Federal do Estado da Bahia. 435p.Brasil. Ministério da Saúde. Portaria n°518/MS, de 25 de março de 2004. Estabelece osprocedimentos e responsabilidades relativos ao controle e vigilância da qualidade da águapara consumo humano e seu padrão de potabilidade, e dá outras providências. Legislação.Disponível em: Hhttp://portal.saude.gov.br/saude/H. Acesso em 15.02.2010.Brasil. Conselho Nacional do Meio Ambiente - CONAMA. Resolução 357, de 17 de marçode 2005. Dispõe sobre a classificação dos corpos de água e diretrizes ambientais para o seuenquadramento, bem como estabelece as condições e padrões de lançamento de efluentes, edá outras providências. Disponível em: Hhttp://conama.gov.brH. Acesso em 25.09.2010.Clesceri, L. S.; Greenberg, A. E.; Eaton, A. D., 1998. Standard methods for the examinationof water and wastewater. 20 th ed. American Public Health Association, Washington. 1325 p.ISBN 0875532357.IAEA. 2002. Instrumentation and control systems important to safety in nuclear powerplants: safety guide. Vienna: International Atomic Energy Agency.Nossa, T. C. B. 2011. Avaliação da vulnerabilidade do aquífero cárstico Salitre - Bahia,através de análises hidroquímicas, isotópicas e aplicação da metodologia COP. Tese deDoutorado, Instituto de Geociências, Universidade Federal da Bahia, 226p.5. AcknowledgmentsThe authors wish to thank the Geological Survey of Brazil (CPRM) for their support duringfield work and the physical-chemical analyzes performed at the Laboratory of Mineral Waters(LAMIN/CPRM) and the Laboratory of Applied Nuclear Physics, Federal University of Bahia(LFNA-CPGG/IF-UFBA) for performing the isotopic analyzes.81

GROUNDWATER HYPERSALINIZATION IN A LOWLAND COASTAL AQUIFER(PO RIVER PLAIN, ITALY)1. INTRODUCTION 82

2. MATERIALS AND METHODS83

3. RESULTS AND DISCUSSIONS 4. CONCLUSIONS84

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHOW TO FACE GROUNDWATER SALINIZATION ANDCONTAMINATION UNDER GLOBAL ENVIRONMENTAL CHANGE IN ITSSOCIETAL CONTEXT: CHALLENGE OF WATER QUALITY IN THEURBAN ENVIRONMENT OF RECIFE (BRAZIL)MONTENEGRO, S.; HIRATA, R.; PETELET-GIRAUD, E.; CARY, L.suzanam.ufpe@gmail.comUFPERua Padre Landin, 302, apto. 1401, Torre, Recife, PEAbstract. Due to an increasing demographic pressure, the Metropolitan Region of Recife(RMR) went through remarkable water and land use changes over the last decades. Theseevolutions gave rise to numerous environmental consequences, such as a dramatic decline ofthe aquifer potentiometric levels, groundwater salinization and contamination. Thisdegradation of natural resources is linked to the increase of water demand, punctuallyamplified by drought periods which induced the construction of thousands of private wells,hindering global political solutions. The RMR thus appears as a typical "hot spot" illustratingthe problems of emerging countries such as urbanization, unequal distribution of wealth,limited effects of political decisions, rapid industrial and touristic developments. All thesefactors induce high pressures on water resources both on quantity and quality in the contextof global social and environmental changes. Under these conditions, the COQUEIRALresearch project proposes an interdisciplinary investigation program aiming to study thehuman impact on coastal overexploited aquifers. The project is structured in three principalconverging axes: (1) the analysis of pressures on the groundwater resources and theirsocietal and structural reasons; (2) the identification of sources and mechanisms ofgroundwater quality and quantity degradation, focusing on the physical and chemicalprocesses as vectors of the reaction of the system to the external pressures; and (3) theassessment of the regional impact of global changes on water resources. This projectapproaches the degradation of the groundwater resources by questioning the specificconditions of urbanization and water administration in Recife at multiple levels: (1) themacro-sociological level with the political and institutional stake of water management; (2)the meso-sociological level with the water’s collective stakes and their perceptions; and (3)the micro-sociological level, meaning the representations, practices, individual and collectiveuses of water. Geomorphological-urban maps will complete the knowledge. In parallel to theacquisition of new geological, hydrological and hydrogeological data, the objective is toelaborate methods to determine the origin and processes of salinization, including a multitracerapproach, to identify sources and pathways of inorganic contamination and todetermine the residence time of water within the aquifers.Keywords: groundwater salinization, societal context, geochemistry, isotope86

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHYDROCHEMISTRY, STABLE ISOTOPES AND PALEOHYDROLOGY OFTHE COASTAL AQUIFER NEAR RAVENNA (ITALY)MOLLEMA, Pauline; ANTONELLINI, A; DINELLI, E; GABBIANELLI, G;GREGGIO, N; STUYFZAND, P. J.pmollema@gmail.comUNIVERSITY OF BOLOGNAVia san Alberto 163, Ravenna, ItalyAbstract. A hydrochemical and stable oxygen and hydrogen isotope analysis in combinationwith a study of the paleohydrology provides insight in to the current hydrochemistry of thecoastal aquifer near Ravenna Italy, with emphasis on the cause of the high salinity present allthroughout the aquifer. Two hundred and twenty nine samples of ground and surface waterwere analyzed for major cat ions, anions and stable oxygen and hydrogen isotopes. Thesamples were grouped according to sampling environment to see if waters coming from thesame background (new or old dunes, lagoons, agricultural fields, quarries, and rivers)showed the same hydrochemistry. The most occurring water type based on the classificationof Stuyfzand (1989) is the brackish to saline NaCl type. Calcium rich water is found only inthe rivers, in the irrigation channels and in a few wells. The stable isotope analysis and theanalysis of tracers such as SO4/Cl- and 18O versus Cl show that most ground watersamples are a mix between fresh water similar to rain or irrigation, river or fresh dune waterand water that is similar to current Adriatic Sea water. Two groups of samples have ananomalous chemical and isotope signature that does not reflect pure mixing of fresh withseawater: One group is chemically very similar to waters that are trapped in sediments of theNorth Sea marshes during the Holocene transgression while the other group of samples isderived in and around current lagoons. Analysis of the paleo-hydrology shows that ourcoastal aquifer was formed during the Holocene transgression. As the sea regressed freshwater infiltrated into the sandy deposits but because recharge areas were small and theamount was reduced by evapotranspiration of pine trees since Roman times, there was notenough infiltration to flush the aquifer completely.Keywords: Hydrochemistry; Stable isotopes; Coastal aquifer; Holocene transgression.87

2 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHYDROGEOCHEMISTRY CHARACTERIZATION OF THE COASTALAQUIFERS IN TAMOIOS DISTRICT / CABO FRIO- RIO DE JANEIRO, BRAZILLuana Alves de Lima 1 ; Juliana Menezes 2 ; Gerson Cardoso da Silva Junior 3 ; Paulo deTarso Luiz Menezes 1luanalimageol@gmail.com1- Faculdade de Geologia, Universidade do Estado do Rio de Janeiro, RJ, Brazil2- Instituto de Ciências da Sociedade, Universidade Federal Fluminense, Campo dosGoytacazes, RJ, Brazil3- Departamento de Geologia, Universidade Federal do Rio de Janeiro, Rio deJaneiro, RJ, Brazil524 São Francisco Xavier street, 20550-900, Maracanã – Rio de Janeiro - RJ, BrazilAbstract. In Rio de Janeiro Eastern Coast, Cabo Frio is one of the areas which undergoesenvironmental pressure caused by human activity, mainly by the intense flux ofvacationers. The area has a homogeneous extension of coastal aquifers, limited by the SãoJoão River, in the North, which is the main river system of the area, and in the South, by theUna River, border with the Búzios municipality. This paper aims to present thehydrogeochemical characterization of these coastal aquifers in District Tamoios. Three mainsteps were necessary: (1) Survey of pre-existing data, (2) Field work for measurement ofphysico-chemical parameters in situ and sampling for chemical, isotopic and microbiologicalanalysis (3) Storage and processing of data collected. The results indicated that in thehydrogeochemical Region Tamoios it is possible to observe higher values of EC in the centralportion of the coastal aquifer. This fact indicates a water salinization in the region near theartificial lakes generated by sand extraction activity. The data indicates that the Tamoiosgroundwater resource has a considerable potential to vulnerability.Keywords: coastal aquifers; hydrogeochemistry characterization; water quality1. INTRODUCTIONSaline Intrusion studies in the Coastline of the Rio de Janeiro State are being developedby several authors. Cruz & Silva Junior (2006), Almeida & Silva Junior (2007), Seabra et al(2007), Tapia et al (2010) developed studies which allowed a better comprehension by thecurrent situation of the this coastal aquifers. For Werner et al. (2012), Saline Intrusionstudies, is a global issue, exacerbated by increasing demands for freshwater in coastal zonesand predisposed to the influences of rising sea levels and changing climates. In this context,one of the counties of the Rio de Janeiro East Coast, Cabo Frio, is one of them, which sufferenvironmental pressure caused by human activity, mainly by the massive influx ofvacationers. Studies demonstrate that in some places the groundwater quality is altered(Menezes et al., 2008). One of the most vulnerable areas is the Tamoios District, 2nd Districtof Cabo Frio (22º37’30’’ S, 42º01’30”W). That region has peculiarities that increase theimportance of the groundwater study. Their boundaries contain important Atlantic Rainforest88

2 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesremnants including the Mico Leão Dourado Municipal Park (belonging to the BiologicalReserve of Poço das Antas Biological Reserve, within the field of Environmental ProtectionArea São João River).The Tamoios District has a homogeneous region of coastal aquifers,limited by the São João River in north, the main river system of the area, and the south by theUna River, border with the Búzios municipality .The hydrogeological potential of the study area is associated by the alluvial and marinesedimentary deposits. These deposits are free and shallow clastic aquifers, extremelyvulnerable. The conditions of the land use and occupation of the physical environment affectthe groundwater quality extract by the tubular wells, in range of 3 and 10 meters. Also,included in the coastal aquifers of the Tamoios District, have a wide range of lakes caused bythe sand mining activity, in the 80 and 90 years. In addition, the Tamoios District has aprecarious sewerage system. The saline water intrusion is associated by the super aquiferexploitation in vacations periods.This study aims at evaluating the current situation of the groundwater resources inCoastal District Tamoios by the hydrogeochemical aquifer characterization, in order todiagnose the vulnerability of this aquifer system.2. METHODOLOGYThree main steps were necessary to ensure the objectives to be met: (1) Survey of preexistingdata (obtaining thematic maps, satellite imagery, geophysical data and literaturesearch), (2) Field work for recognition of the study area, measurement of physico-chemicalparameters in situ sampling for chemical analysis and microbiological laboratory isotopicand (3) Storage and Processing of data collected in a Georeferenced Database (GDB).The first field campaign took place from 9 to 13 August 2010 and had two main objectiveslisted: 1. Registration of wells, as well as the measurement of physico-chemical parameters insitu: pH, EC (Electrical Conductivity), T (temperature) and TDS (Total Dissolved Solids) 2.Based on the registered points, selection and collection of 10 water samples for analysis ofmicrobiological, chemical and isotopic data. Seven of these ten samples consist ingroundwater samples and three surface water samples related to the São João River, UnaRiver and one of in the artificial lake. The chemical and microbiological analysis were sent toAnalytical Solutions Company (ANASOL) for the determination of the major groundwaterelements (Na + , K + , Mg 2+ , Ca 2+ , Cl - , HCO 3 - , SO 4 2- ). Samples for isotopic analysis were sent tothe GeoChronos Laboratory of Geosciences Institute at the University of Brasilia (UNB) todetermine the rates of O18 and deuterium (2H).At first, the data obtained in situ from field campaign, were processed in a spatialenvironment of GIS (Geographic Information System), using the software of ESRI ArcGIS10.0. Were generated Contour maps showing CE and TDS through the use of Spatial Analysttool, and the use of available interpolation method on the same (Inverse Distance Weighted)could perform the spatial distribution of these parameters for all study area. The secondphase of analysis consisted in storing the data obtained from chemical for graphinghydrogeochemical in the software Aquachem5.0 of Schulumberger Water Services todetermine the main hydrochemical facies.89

2 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives3. RESULTS AND DISCUSSIONSIn general the results indicated in that the hydrogeochemical Region Tamoios is possibleto observe higher values of EC in the central portion of the coastal aquifer, to the detriment ofneighboring regions that are bordering the São João River and Una River. The TotalDissolved Solids have values ranging from 35 to 1050 ppm, and the maximum allowablevalue by legislation in Resolution No. 396 of CONAMA (Environmental National Council) forhuman consumption is 1000 ppm showing the possible groundwater contamination near theartificial lakes. An evidence that can justify the salinity in the central portion is that the lakesprovide the outcrop of the water-bearing stratum, where the waters of granular aquifersystem have its flow toward the lakes contributing the advancement of salt water intrusion.This trend does not occur with nearby wells measured with the Una River and Sao JoãoRiver, where it probably has a freshwater inflow.According to the Piper diagram (Figure 1a), which could also show the averagecompositions of freshwater and seawater (Appelo & Postma, 2005) the groundwater of thisregion indicates a mixing of salt water and freshwater. The samples nearby the coastalpresent a trend of salt water intrusion, which major elements are chloride and sodium. Thethree surface water samples indicate a strong sea influence in their chemistry. The Piperdiagram also demonstrates that the main groundwater types are calcium bicarbonate andsodium chloride waters. The salinity trend of the artificial lake sample can be related to theabsence of circulation and water renewal, and low dilution by recharge. It can also beattributed to the advancement of the salt water .The isotopic signature of the groundwatersamples indicate that all of them present similar concentration, and therefore have the sameorigin. The rate of Deuterium and O18 shows that the main recharge is caused by themeteoric waters. The isotopic rates of surface water demonstrates that they have the sameorigin, they are influenced by the aquifer water due to the fact they were collected during adry weather period (Figure 1b). As a conclusion groundwater, especially near the areas ofartificial lakes, has compromised quality, determined mainly by the high rates of EC,indicating progress in this part of the salt water intrusion. The Total Dissolved Solids valuesexceed the Maximum Permited Value by legislation in the well near the artificial lake, and allanalyzes prove that improper according to the fecal and total coliforms. The data indicatethat, according to the hydrogeological point, the Tamoios region has considerably vulnerableto contamination and represent a risk to health. The studies will be detailed in this context bymapping mapping the vulnerability the advancement of the salty water intrusion in order toassess more accurately the contamination processes and in order to provide a managementtool for effective sustainable management of groundwater in this region.90

2 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFigure 1- A, the piper diagram and B the isotopic ratios of H2 and O18 to the superficial and groundwater samplesaccording the Viena Standard Mean Ocean Water – VSMOW.REFERENCESAlmeida G.M. and Silva Jr., G.C. 2007. Hydrogeological factors in the study of salineintrusion of the coastal aquifer of Maricá City, Rio de Janeiro, Brazil. Anuário doInstituto de Geociências – UFRJ, vol. pp. 104-117. [In Portuguese].Appelo C. A. J. and Postma D. 2005. Geochemistry, groundwater and pollution. A.A.Balkema Publishers, Leiden, The Netherlands 2 nd edition.Cruz, A.; Silva Jr., G. C. 2006. Spatial and temporal hydrochemical behavior of Piratiningacoastal aquifer. Niterói City, Brazil. In: 19 th Salt Water Intrusion Meeting, Cagliari,Italy. Proceedings of the 19th SWIM. Cagliari : U. Cagliari. v. 1. pp. 12-18.Menezes, J.M.; Santos, R.T. DOS; Silva JR., G.C. DA., Prado, R. B. 2008. StakeholdersIdentification: A tool to evaluate the groundwater quality. In: XV Groundwater BrazilianCongress. Natal: ABAS, 1 CD-ROM [In Portuguese].Seabra, V. S.; Silva Junior, G.C.; Cruz, C.B.M. 2008.The Use of Geoprocessing to AssessVulnerability on the East Coast Aquifers of Rio de Janeiro State, Brazil. EnvironmentalGeology (Berlin), vol. 55, pp. 1345-6.Tapia, A.P.; Almeida, G.M.; Silva Junior, G.C.; Waterloo, M. 2010. Coastal aquifers of Barrade Maricá, Brazil: contamination and saline wedge behavior. In: 21 th Salt WaterIntrusion Meeting. Azores, Portugal. Proceedings of the 21th SWIM: pp. 39-42.Werner, A.D; Bakker, M.; Post, V.E.A.; Vandenbohede, C.L.; Atail-Ashtiani, B. Simons,C.T.; Barry, D.A. 2012. Seawater intrusion processes, investigation and management:Recent advances and future challenges. Advances in Water Resources, In Press,Corrected Proof, Available online 19 March 2012.91

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesIMPORTANCE OF BEACH WELLS INTAKES FOR SUPPLYING REVERSEOSMOSIS (RO) DESALINATION PLANTSSOLA, F.; VALLEJOS, A.; PULIDO-BOSCH, A.avallejo@ual.esUniversity of Almería (SPAIN)Department of Hydrogeology. University of Almería. 04120 Almería (Spain)Abstract. The method of seawater capture for supplying reverse osmosis (RO) desalinationplants is a key factor in determining the cost of the desalinated water, and a significant factorinfluencing the useful life of the membranes and the plant as a whole. The two abstractionmethods most commonly used are open seawater intake and beach well systems. Directseawater intake is the most widely used technique since it requires relatively simple andcheap infrastructure, and is capable of delivering large seawater flows to the plant butcoastal boreholes (beach wells) offer the possibility of supplying better quality water to thedesalination plant: the aquifer formation filters the water before it reaches the plant, soreducing pre-treatment costs. This study focuses on the role of the aquifer media as a tool toimprove the characteristics of seawater used to supply desalination plants. The experimentconsisted of drilling three boreholes aligned perpendicularly to the coast; the one furthestinland was used as the pumping well to simulate the operation of beach wells that supplydesalination plants. The other two boreholes were used as observation piezometers to monitorthe changes in the physical, chemical and microbiological characteristics that take placealong the flow path between the sea and the pumping well. The pilot scheme was installed onthe left bank of the delta of the river Andarax, in southeastern Spain. By comparing thecomposition of seawater taken via direct intake with the water sampled over the aquifer, itmay be able to determine the evolution of both physico-chemical and microbiologicalcharacteristics through the aquifer media. One of the most significant modifying process ision exchange which, in this context, usually involves fixing of ions like Na+ and K+, andliberation of Ca2+. The principal improvements are due to the process of filtration, whichmarkedly reduces the SDI (Silt Density Index) and water turbidity, as well as dissolvedoxygen and organic matter. It includes up to a 95% reduction in turbidity and up to a 50%reduction in SDI. Other parameters are also notably reduced (TOC is cut on average by 60%,and DO by 80%), due to bacterial activity in the aquifer. The calculated transit time from themoment the water enters the aquifer to its abstraction is approximately one week. Thereductions that are known to take place in borehole abstractions occur in the first few metresof the aquifer transit.Keywords: seawater intake; filtration processes; water-rock interaction; aquifer matrix92

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSALINITY VARIATIONS OF ITABORAÍ SEDIMENTARY AQUIFERSGomes, Olga. V. O. 1,2 ; Aires, José. R. 3 , Marques, Eduardo. D 4 , Silva-Filho, Emmanoel. V. 2olga_gomes@ufrrj.br1 - Departamento de Ciências Administrativas e do Ambiente, Instituto Três Rios,Universidade Federal Rural do Rio de Janeiro, Três Rios, RJ 25802-180, Brazil.2 - Departamento de Geoquímica, Instituto de Química, Universidade Federal Fluminense,Niterói, RJ 24020-141, Brazil. E-mail: geoemma@vm.uff.br3 - ABAST, PETROBRAS, Rio de Janeiro, RJ 21.949-900, Brazil.4 - CPRM - Serviço Geológico do Brasil, Belo Horizonte, MG 30140-002, Brazil.Email:eduardo.marques@cprm.gov.brAbstract. The hydrogeochemistry of sedimentary aquifers in municipality of Itaboraí wasstudied from August 2009 to January 2010, where were verified different salinity valuesamong Macacu, Aluvial-Lacustrine and Fluvial-Marine aquifers. This work presentsinformation about the source of dissolved constituents of the Macacu sedimentary basingroundwater by physico-chemical parameters, hydrodynamics analysis and rCl/rBrassociated to the dissolved organic carbon (DOC). The rCl/rBr pointed out four differentsources of groundwater basin. The Group 1 is formed by groundwater from recharge area,with rCl/rBr = 100 - 539 and Cl concentrations lower than 25 mg L -1 . Those waters belong toMacacu aquifer and are influenced by meteoric waters. The Group 2, which is located in adischarge area, presents rCl/rBr = 1007 – 1500 and Cl concentrations ranging from 141 to178 25 mg L -1 . Those waters come from the Aluvial-Lacustrine aquifer system and some partfrom Macacu aquifer in Itambi region. The Group 3 is formed by groundwater that showedrCl/rBr = 10 – 591 mg L -1 and Cl concentrations about 443 – 745 mg L -1 . Those watersbelong to the Aluvial-Lacustrine aquifer system (Porto das Caixas region) with high Clconcentrations, however, relevant Br concentrations linked to the organic matter. The Group4 is formed by groundwater with rCl/rBr = 274 – 595 and the highest Cl concentrations (803– 1246 mg L -1 ). Those waters make part of Fluvial-Marine aquifer in the mangrove region ofGuapimirim APA, where occurs marine intrusion.1. INTRODUCTIONThe Guanabara Bay Basin is located in the Rio de Janeiro Metropolitan Region andintegrates the Macacu sedimentary basin, where occurs the Macacu aquifer, formed byTertiary sediments with can reach thickness more than 200 meters besides the Quaternaryaquifers, which are formed by alluvial-lacustrine and fluvial-marine sedimentary facies andthey reach thickness about 40 meters (Figure 1).The monitoring carried out in those aquiferssystems detected significant salinity variations in the three aquifers system, which consider97

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesthe ratio chloride/bromide. Once dissolved in water, Cl and Br preserve the record ofdissolved material which originates the groundwater salinity (Alcalá & Custodio, 2000).Considering not only the marine aerosols as the main reason of salinity in groundwater, thesalinity can also be influenced by lithology and anthropogenic activities and the study of therCl/Br ratio together to the Cl concentrations provide information about residence time ofgroundwater in that region.Figure 01: Geology from the Macacu sedimentary basin and the location of monitoredwells. Source: Meis e Amador, 1977; Penha, 1979; D’alcolmo, 1982, Ferrari e Ferraz,1988.2. MATERIAL AND METHODSSix sampling campaigns from August 2009 to January 2010 were carried out, monitoring fivewells and four of them are multilevel wells (P-01, P-02, P-03 and P-04) with inflow in two orthree depths ranging from 17 to 148 m. Only the well P-05, located in the mangrove area, hasone inflow depth, about 15 m, where were verified the maximum and minimum values ofelectrical conductivity (EC), pointing out tidal influence. The EC in the monitored wellsranged from 48 to 5651 S cm -1 . The Cl and Br analysis, carried out without dilution by ionchromatography, were used to in order to distinguish the salinity sources of Macacu Basingroundwater through the rCl/rBr ratio.98

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives3. RESULTS AND DISCUSSIONIndependent of the season and the type of aquifer, it was observed the wells far 14 km fromthe coast as the P-01, P-04 e P-05 presented EC values higher than the others. The hypothesisof those wells would be linked to an influence area of saline wedge or linked to a process ofstrong lixiviation of the sediments from ancient marine facies.The sampled area never ever been used as waste disposal area nor an area with great urbanactivity, thus, the salinity found in that area has no anthropogenic influence. The Figure 2presents the Cl/Br ratio as a hydrogeological tracer of salinity in the studied aquifers andassociated to Cl concentrations it become possible to discriminate four main groups ofgroundwater sources.The Group G1 is formed by groundwater from recharge area, with rCl/rBr = 100 - 539 andCl concentrations lower than 25 mg L -1 . Those waters belong to Macacu aquifer and areinfluenced by meteoric waters. The Group G2, which is located in a discharge area, presentsrCl/rBr = 1007 – 1500 and Cl concentrations ranging from 141 to 178 25 mg L -1 . Thosewaters come from the Aluvial-Lacustrine aquifer system and some part from Macacu aquiferin Itambi region (P-04). Although the high rCl/rBr values, this group showed low Clconcentrations compared to the others studied aquifers systems.The distinction of rCl/rBr values from G2 is given mainly by the location of P-04. The lavelsA and B of this well are found in Itambi region, where the groundwater flows away throughlacustrine mudstones from Rio Vargem Member (Macacu Formation). That lithology couldcontain some precipitated salts as halite in its composition.The Group G3 is formed by groundwater that showed rCl/rBr = 10 – 591 mg L -1 and Clconcentrations about 443 – 745 mg L -1 . G3 is formed by groundwater from Alluvial-Lacustrine aquifer from Porto das Caixas region (P-01C). The G3 groundwater has highconcentrations of Cl, but also high Br concentrations, which reduces the rCl/rBr. This wellhas high Cl concentration and it should be linked to the sewage releasing that comes fromCaceribu River, located about 350 m from P-01C.Regarding the low Br concentrations, Davis et. al. (op. cit.) showed that shallow groundwatercan present low rCl/rBr in aquifers with significant content of organic matter. In Porto dasCaixas region (well P-01C), the rising of Br concentrations is close related to the dissolvedorganic carbon (DOC). The relationship between DOC and Br is not relevant for the othersaquifers systems.The Group G4 is formed by groundwater with rCl/rBr = 274 – 595 and the highest Clconcentrations (803 – 1246 mg L -1 ). G4 has groundwater from the Fluvial-Marine aquifersystem in Guapimirim APA region. Hydrodynamics and isotope analysis confirm for thisaquifer the rising of Cl concentrations is related to marine intrusion (saline wedge). Thisregion is formed by mudstones rich in organic matter, which also has high Br concentrations,but the marine intrusion generally maintains high rCl/rBr values. Nevertheless, in periods oflow tide, Br content of organic matter can influence the rCl/rBr, denoting values less than500 as verified in some samples from Fluvial-Marine aquifer.99

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFigure 2: rCl/rBr associated to the Cl concentrtions in the Itaboraí sedimentary aquifers.REFERENCESAlcalá, F. J.& Custodio E. (2004). La Relacion Cl/Br como indicador del origem de lasalinidad en algunos acuíferos de España y Portugal. Groundwater Flow Understanding,from Local to Regional Scale. XXXIII Congreso Intern. Assoc. Hydrogeologists–ALHSUD. Zacatecas. 4 pp.Davis, S. N.; Whittemore, D.O. and Martin, J.F (1998). Uses of Chloride/Bromide Ratios inStudies of Potable Water. Vol.36,n o 02, Ground-Water. 338-350p.Cartwright, I.; Weaver, T.R.; Fifield, L.K. (2006) Cl/Br ratios and environmental isotopes asindicator of recharge variability and groundwater flow: Na example from the southeastMurray Basin, Australia. Chemical Geology. 231. 38-56p.ACKNOWLEDGMENTSTo INCT-TMOcean (CNPq) for the support on this study.100

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSANTA CESAREA COASTAL THERMAL SPRINGS (SOUTHERN ITALY)M. Polemio, P. P Limoni, L. E. Zuffianò, F. Santaloiam.polemio@ba.irpi.cnr.itIRPI, CNR, Bari, Italy.Abstract. The coastal carbonate Apulian aquifers, located in southern Italy, feed numerouscoastal cold springs and constitute the main local source of high quality water. The group ofSanta Cesarea springs constitutes the unique occurrence of thermal groundwater outflow,observed in partially submerged coastal caves. The spring water is rich of hydrogen sulfide;temperature ranges from 25 to 33 C°. For their properties, spring waters are used for spaactivities from several decades. Hydrogeological spring conceptualisations proposed up nowwere not able to justify water geochemical peculiarities or were not completely confirmed upnow. To reduce these uncertainties, a complex hydrogeological survey has been defined.Geological and structural surveys, chemical and isotopic groundwater analyses, spring andwell discharge measurements, well loggings, multi-parameters spring automatizedmeasurements, and cave explorations are ongoing. All available data have been used toimprove the knowledge of groundwater flow system, including the valuable deep aquifer, theorigin of the thermal waters, and to investigate the possibility of using low-enthalpygeothermal fluids to fulfil the thermal needs of the town of Santa Cesarea Terme.Keywords Carbonate aquifer; sulphur groundwater; thermal springs, coastal aquifer,Apulia, Italy1. INTRODUCTIONThe Santa Cesarea spring group is located in the town of Santa Cesarea Terme (terme is theItalian translation of spa), a touristic villages of Salento, the south-easternmost portion of theApulia region (Southern Italy; Figure 1). These springs are characterized by sulphureous andwarm waters (Zezza, 1980). Their special groundwater characteristics were discovered inancient times and were described by historians, such as Aristotele (III century BC), Strabone,Claudiano, Leto (I, III, and XV century respectively), as well as by recent authors. Springwater characteristics are almost variable as consequence of tides (Visintin 1944; Zezza 1988).In particular, the ion chloride content increases with tides, while the hydrogen sulphidecontent and temperature decrease. The paper presents some preliminary results of an ongoingresearch project of the (Italian) National Research Council, aimed at the assessment of thegeothermal potential of regions located in southern Italy (VIGOR Project).2. GEOLOGICAL AND HYDROGEOLOGICAL SETTINGSThe Santa Cesarea group is represented by four main springs, located in Salento Peninsula,along about 500 of the Adriatic coast, where the outcropping limestone of the Apuliancarbonate platform is dissected by a series of NO-SE faults dipping towards East and West.101

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesOffshore, the carbonate sequence underlies athick succession of Quaternary sediments,which forms the foredeep in-fill of Dinaricchain (Figure 1). Salento peninsula is part ofthe Apulia carbonate platform, part of theAfrican passive margin. The main geologicalunits outcropping in the study area, extendedalong the coast between Porto Badisco andCastro, are represented by (i) a carbonatesequence constituted by Cretaceous andOligocene limestones, intensely fissured andkarstified; (ii) a Miocene calcarenite; (iii)Figure 1. Location of study area.Pliocene weakly clayey sand and (iv)Pleistocene calcarenite (Figure 2).The main aquifer, called “deep aquifer”, is constituted by the Mesozoic limestone of Apulianplatform (Oligocene limestone is not relevant at the aquifer scale). The maximum piezometrichead is less than 4 m asl in the whole Salento. Where limestone does not outcrop, calcareniteand sands can constitute a shallow narrow aquifer. The aquifer’s base level corresponds to thesea level; fresh groundwater, flowing over saline water of sea origin, outflow trough severalcoastal springs.As concerns the origin of the sulfide in the spring waters, according to Zezza (1980), it shouldbe due to the reduction of sulphate contained in the seawaters which occurs when these waterscome into contact with the organic matter included in the Miocene calcarenite layers. Thisreduction would occurs by means of an exothermic chemical reaction warming locally theflowing groundwater. The origin proposed by Zezza (1980) was also substantiated by Calò(1991). On the other side, according to Maggiore and Pagliarulo (2004), warm deep fluids,flowing below the Adriatic Sea, rise through the pre-pliocenic carbonate substratum,explaining the spring water peculiarity. The flow of these connate water should be due to thetectonic “pressure” of the Dinaric-Hellenic thrust-sheets convergence toward the Apulianforeland.3. FIELD AND LABORATORY DATATemperature, electrical conductivity, dissolved oxygen, redox potential, pH, alkalinity(titration with HCl) and SiO 2 (determined using a portable colorimeter) have been determinedin the field. Cations (Ca 2+ , Mg 2+ , Na + , K + ) and anions (Cl - , SO 4 2- , NO 3 - ) were analyzed bymeans of ion chromatography (IC) methods. The overall precision of the analyses based onmajor ions is within 5%. Data processing was carried out using the PHREEQC software. Thelocation of sampling points is shown in Figure 2. Ion chromatography results and the waterclassification are shown in Figure 3.The diagram show that the sample 3, fresh groundwater, lies in the (Ca+Mg)–(HCO 3 ) field,and represents the typical groundwater of Salento peninsula. The samples 4 and 5 are amixture of fresh groundwater and sea water. The thermal groundwater has higher total102

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFigure 2. Hydrogeological schematic map: 1)continental deposits (Quaternary); 2) calcarenite(Pleistocene); 3) weakly clayey sand (Pliocene); 4)calcarenite (Miocene); 5) limestone (Cretaceous-Oligocene); 6) well; thermal 7) well and 8) spring;9) fresh spring; (10) groundwater temperature.dissolved solids (58000 mg/L, sample 2) withrespect to fresh groundwater (generally up to500 mg/L). The temperature of thermalgroundwater varies from 25 C to 33 C.Some thermal groundwater samples (1, 2, S1,S6) are located close to the point whichrepresents the composition of seawater, witha enrichment in Ca 2+ and Mg 2+ , relative toNa + and K + ions.Minor and trace elements were determined byinductively coupled plasma massspectrometry (ICP-MS). Thermal waters arechemically characterized by highconcentration of Li + , Sr 2+ , F - and Br 2+ . Mostof the trace element concentrations are relatedto the redox environment of thermal waters.The redox potential values range, for some ofthe samples, from negative to slightly positive(-300 mV to 30 mV), corresponding toreducing environments.The D/H isotopic ratios have been plotted in a18O–D diagram (Craig, 1961) shown inFigure 4 where the Global Meteoric Water (GMWL) and the Mediterranean Meteoric WaterLines (Gatt and Carmi, 1970) are also reported. The sample of cold water (3) falls betweenthe Global Meteoric Water Line and the Mediterranean Meteoric Water Lines, suggesting so ameteoric origin of this sample. Samples 1, 2 and S2 plot to the right side of the GMWL andthe MMWL lines, indicating so an enrichment in oxygen 18 O. It could be simply justifiedconsidering the interaction of ions in solution and water molecules in a fluid system at highsalinity, even at low temperature (Gonfiantini, 1986). Moreover, since the salinity of thesesamples seem to be high, a certain contribution of isotopically heavy connate waters couldoccur.The studied water samples are undersaturated with respect to calcite and dolomite as resultedfrom the calculations of equilibrium of waters with these carbonates.CONCLUSIONThe thermal system of Santa Cesarea, which has been used for spa from several decades,seems essentially due to three water types or components: 1) pure fresh groundwater thatderives from meteoric infiltration in the carbonate outcrops, 2) saline water due to seawaterintrusion, 3) a thermal saline fluid rich in sulphur. The resulting mixture is undersaturatedwith respect to calcite and thus aggressive. Bögli (1964) considered “mixing corrosion” thekey process for karstification. Previous conceptualizations of Santa Cesarea springs do notseem to be fully coherent with available preliminary results. Very high salinity and high103

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivestemperature of the third water type seem dueto the interaction water-carbonate rocks,defining an almost steady fluid system at highsalinity, even at not particularly hightemperature.The completion of surveys, which will beenlarged thanks to deep geophysicalcampaigns, should be sufficient to clarify thesource of third-type water, the source ofpressure forced out these waters, justifyingthe steady characteristics of their outflows.REFERENCESBogli, A., 1964. Mischungskorrosion einFigure 3. Langelier-Ludwig diagram of analyzed Beitrag zum Verkastungsproblem. Erkundegroundwater samples18, 83-92.Calò, G., & Tinelli, R., 1995. Systematichydrogeological study of a hypothermalspring (S. Cesarea Terme, Apulia), Italy.Journal of Hydrology, vol 165, pp 185 – 205.Calò, G., Spizzico, M., Tinelli, R., & Zezza,F., 1983. Hydrogeological investigations onthe area sourroundig santa Cesarea TermeSprings (Southern Apulia), GeologiaApplicata e Idrogeologia, vol XVIII, pp 129 –144.Craig, H., 1963. Isotopic variations inmeteoric waters. Science 123, 1702–1703.Gatt, J.R., & Carmi, I. 1970. Evolution of theisotopic composition of atmospheric waters inthe Mediterranean Sea area. J. Geophys. Res.Figure 4. Binary D - 18O diagram for some of the 75, 3032 – 3048.samples investigated.Gonfiantini, R., 1986. Environmental isotopesin lake studies. In: Fritz, P., Fontes, J.Ch.(Eds.). Handbook of Environmental Isotope Geochemistry, Elsevier. pp. 113–168.Maggiore, M., & Pagliarulo, P., 2004. Circolazione idrica ed equilibri idrogeologici negli acquiferidella Puglia. Geologi e territorio, n. 1/2004. pp. 13-35Visintin, B., 1944. Studio dell’acqua della grotta Gattulla delle Terme demaniali di S. Cesare.Rendiconto Istituto Superiore Sanità, vol. VII, p. II.Zezza, F., 1980. Le sorgenti ipotermali solfuree di Santa Cesarea Terme. Azienda di cura esoggiorno e turismo Santa Cesarea Terme. Estratto dalla rivista quadrimestrale dicultura e civiltà salentina “Salentum” - Anno III nn. 1–2 – edita dall’E.p.t. di Lecce.104

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesUNDERSTANDING THE ORIGIN OF SALINIZATION OF THE COASTALAQUIFER OF SOUSSE (TUNISIA) USING GEOCHEMICAL AND ISOTOPEINVESTIGATIONSHAMOUDA, Mohamed Fethi Ben; CARREIRA, P.; EGGENKAMP, H.;MARQUES J.M.f_benhamouda@yahoo.frCNSTN, Tunisia; ITN, Portugal; UTL, PortugalCNSTN, UHGI, Technopark of sidi Thabet, 2020, TunisiaAbstract. Simulation of saltwater transport is an essential tool to understand environmentalproblems such as saltwater intrusion in coastal aquifers,landfills leakage, radioactivedisposals in salt rock formations and subsurface dissolution of evaporites. Subsaturatedgroundwater in contact with evaporitic rock formations results in rapid subsurfacedissolution or subrosion of evaporites. The process leads to both karst development andsalinization of aquifers. Depending on the geological setting the subrosion may causewidespread land subsidence. The factors controlling formation and shape of deep-seatedsubrosion, however, are poorly understood. A crucial point is to understand the role andpathways of water subsaturated with NaCl, or CaSO4 and its driving energy, such asprovided by a hydrostatic head differences, or density gradients, which causes groundwaterto flow through the system. To address the problem, results of experiments and modelingapproaches are presented, including: (1) a combination of flow tank and modelingexperiments to study the effect of density-driven flow in heterogeneous media, and (2) a seriesof 2D density-coupled solute transport simulations along an approximately 1000-m long and150-m deep 2D cross section, which represents a setup of two aquifers connected bysubvertical normal fault zones. The resulting high contrasts in groundwater density weresimulated at both laboratory and field scale with a numerical model based on Mixed FiniteElements for the fluid flow problem and a combination of Discontinuous Galerkin FiniteElement and Multi- Point Flux Approximation methods for the transport. The experimentalflow tank data are presented as benchmark problems to evaluate numerical codes. Simulationresults of the 2D cross section indicate that the upconing process of saline groundwater intothe main aquifer occurs under different distributions of subsurface parameters and hydraulicboundary conditions. The simulations also revealed that the most sensitive factor for thedissolution rate is the structure or dip of the halite formation, with an increase of dissolutionrate with increasing dip. As a result of the increased density of the brine, an independent flowdynamic develops that follows the direction of the dip.Keywords: Geochemistry; isotopes; groundwater salinity; Tunisia105

Management of aquiferswith saline groundwater.Salinization prevention,control and remediation

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA JOINT PILOT PROJECT OF GEOLOGICAL SURVEY OF HAMBURG ANDHAMBURG WATER TO MITIGATE GEOGENIC SALT WATER INTRUSIONJohannes Michaelsen 1,5 ; Gesa Barkawitz 2 ; Jens Kroeger 3 ;Björn Panteleit 2,4 ;Frank Skowronek 5jmichaelsen@consulaqua.de1 CONSULAQUA Hamburg; 2 University of Bremen; 3 Geological Survey of Hamburg(BSU); 4 Geological Survey of Bremen; 5 HAMBURG WASSERCONSULAQUA Hamburg, Ausschlaeger Elbdeich 2, 20539 Hamburg GermanyAbstract. Six out of 17 active waterworks of the public water utility HAMBURG WASSERare threatened by geogenic saltwater intrusion. A sustainable use of the groundwater requiresextensive knowledge of the hydrogeological situation, particularly the salt water intrusionprocesses as well as an adapted well field management.The Hamburg Authority of Urban Development and Environment is the approving authorityfor water abstraction in Hamburg. Especially at sites threatened by salt water intrusion, it isessential for the approving authority to have a reliable basis for decisions concerning thesustainability of water abstraction.The result of the presented project is a three-dimensional model (GOCAD) of the currentlocalization of the transition zone between freshwater and saltwater in the investigation area atsouth-east of Hamburg. The model provides information for optimizitation of Monitoring aswell as for prediction of the movement of the fresh-saltwater interface in relation togroundwater abstraction. Within the next years the model of groundwater salinization will beextended to the whole Hamburg metropolitan area. In the future, the joint and comprehensivedata set is available for both stakeholders at Hamburg.Keywords:salt dome, geogenic salt water intrusion, 3-D GOCAD model, Hamburg109

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONThe presented project was initiated by the SWIM 23 working group (organizing committee)and will be implemented in a project of the Department of Geosciences of the University ofBremen.Six out of 17 active waterworks of the public water utility HAMBURG WASSER arethreatened by saltwater intrusion. A sustainable use of these waterworks requires extensiveknowledge of the hydrogeological situation, particularly the salt water intrusion processes aswell as an adapted well field management. Insufficient knowledge or inadequate welloperation or both lead to critical situations and in the worst-case scenario to complete failureof the well field due to salt water intrusion.The Hamburg Authority of Urban Development and Environment is the approving authorityfor water abstraction in Hamburg. Especially at sites threatened by salt water intrusion, it isessential for the approving authority to have a reliable basis for decisions concerning thesustainability of water abstraction. In this regard, the Geological Survey of Hamburg isdeveloping a three-dimensional geological model for the metropolitan region of Hamburg.2. APPROACHANDRESULTSOne of the most important basics for the technical assessment of groundwater extraction is acomprehensive and regularly operated groundwater monitoring network. The monitoringnetwork delivers more or less highly resolved, mostly steady-state, two dimensional data ofthe salinization in the catchment of the affected well field (fig. 1, 2). To ensure a stable solutetransport in groundwater, being mandatory for permanent groundwater abstraction in areasaffected by salt water intrusion, this information is insufficient. The crucial transition zone ofsaltwater to freshwater has a complex three-dimensional structure that requires at least athree-dimensional model, considering the temporal component, even a four-dimensionalmodel. The basic principle is a depth-oriented analysis of all available groundwater datacombined with, e.g., extensive geoelectrical data including an adequate spatial presentation ofthe results. This approach is currently established for a selected area in the Vier- andMarschlande region of Hamburg. One of the largest waterworks of HAMBURG WASSER islocated in this region, abstracting 15% of the total discharge of the utility from a deep aquiferpartly affected by salt water intrusion. In the current survey archived data of the waterworksand the authorities are screened for neglected drill data. All data useful for the spatial analysisof salt water distribution are assessed e.g., geophysical logs, analysis data, measurements ofconductivity and temperature as well as airborne electromagnetic data. This requires theapplication of various software packages for three-dimensional structural analysis (GOCAD),for drill data collection and analysis (GeoDIN) as well as standardized data bases.In the subsurface of Hamburg region several salt diapirs are present (fig. 1). These salt domesdiffer in the vertical distance from top of the dome to the ground surface (fig. 1, 2).Dissolution of salt leads to saline groundwater. The geological strata Hamburg Clay andLower Hydrous Mica Clay represent important aquitards at the study site (fig. 3). Aquitardwindows may lead to upwelling of groundwater. The buried valleys, formed by meltingwaters during late Ice Age, exhibit preferential flow paths of groundwater. Figure 3 displays ageological cross section in the vicinity of the waterworks of Curslack. Within the exploitedaquifer some extraction wells are already underlain by saline groundwater.110

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 1: Area of the city of Hamburg including the investigation area at the south-east, the monitoring wells withrespect to the degree of salinization of groundwater and the well field of the waterworks Curslack.111

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 2: Area of investigation, the monitoring wells with respect to the degree of salinization of groundwater, thewell field of the waterworks Curslack and the location of the north-south geological section shown in Fig. 3.112

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 3: North-south section displaying main geological features and the location of transition zone of fresh andsalt water.The result of the project will be a three-dimensional model of the current localization of thetransition zone between freshwater and saltwater in the model area of Hamburg. In the future,the joint and comprehensive data set will be available for the stakeholders at HAMBURGWASSER, as well as their subsidiary company CONSULAQUA Hamburg and the HamburgAuthority of Urban Development and Environment as a basis for planning admissible groundwater discharge and for high quality assessment of the groundwater resources.113

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesAN INJECTION-EXTRACTION WELL PAIR: A POSSIBLE STRATEGY TOENHANCE GROUNDWATER WITHDRAWAL IN COASTAL AQUIFERSLU,Chunhui; Werner, A. D.; ROBINSON, N. I.; SIMMONS, C. T.; LUO, J.chunhui.lu@flinders.edu.auFLINDERS UNIVERSITYGPO Box 2100, Adelaide, SA, Australia 5001Abstract. An injection-extraction well pair is introduced in this study to maximisegroundwater extraction from a coastal aquifer and prevent seawater intrusion. The well pairis operated by extracting freshwater through a landward well and partially reinjecting intothe aquifer through an injection well located between the interface toe and the extractionwell. The maximum net extraction rate of the well pair, i.e., the difference between theinjection rate and the maximum extraction rate, is examined. Complex potential theory isemployed to derive an analytical solution for the maximum net extraction rate andcorresponding stagnation-point locations and recirculation ratio, assuming steady-state,sharp-interface conditions. The injection-extraction well-pair system outperforms atraditional single extraction well in terms of net extraction rate for a broad range of wellplacement and pumping rates, which is up to 50% higher for an aquifer with thickness of 20m, hydraulic conductivity of 10 m/d, and freshwater influx of 0.24 m2/d. Sensitivity analysesshow that for a given freshwater discharge from an inland aquifer, a larger maximum netextraction is expected in cases with a smaller hydraulic conductivity or a smaller aquiferthickness, notwithstanding physical limits to drawdown at the pumping well that are notconsidered here. For an extraction well with a fixed location, the optimal net extraction ratelinearly increases with the distance between the injection well and the sea, and thecorresponding injection rate and recirculation ratio also increase. If the injection welllocation is fixed, the recirculation ratio (under conditions of maximum net extraction)between the two wells asymptotes to a limiting value with increasing injection rate, and themagnitude of this limiting value depends on the locations of the two wells. The analyticalanalysis in this study provides initial guidance for the design of well-pair systems in coastalaquifers, and is therefore an extension beyond previous applications of analytical solutions ofcoastal pumping that apply only to extraction or injection wells.Keywords: Well pair; Groundwater withdrawal; Potential theory; Coastal aquifer114

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesAN INNOVATIVE APPROACH FOR SUSTAINABLE GROUNDWATER EXTRACTIONIN NATURE RESERVES THREATENED BY SALTWATER INTRUSIONJohannes Michaelsen 1 ; Soeren Kathmann 1 ; Kai Radmann 1 ; Caroline Schlegel 1jmichaelsen@consulaqua.de1 CONSULAQUA HamburgCONSULAQUA Hamburg, Ausschlaeger Elbdeich 2, 20539 Hamburg GermanyAbstract. The water supply of the North Sea islands has relied in the past on the exploitationof the freshwater lenses. As a result of an increasing demand during the last decades, saltwater intrusion has become a more severe problem. Geologists and engineers often succeed inthe application of effective practices in the prevention of saltwater intrusion. These aresometimes inhibited by environmental protection interest groups. The ecologists’ concern isthat critical groundwater-dependent ecosystems may be damaged by lowering of groundwaterdrawdown. The use of alternative water resources will multiply the price of tap water. Thespecification of alternative water supply systems, e.g., desalination or long distance transportby pipelines often has decisive negative effects on the environment as well. Hydrogeologistsand ecologists should investigate in detailed groundwater dependent ecosystems withininterdisciplinary projects in order to develop new concepts for sustainable groundwaterexploitation. The water extraction regime should be dynamically adapted to localmeteorological and ecological constrains on one side and public water demand on the otherside.Keywords: groundwaterdependent ecosystem, soil hydrology, islands, dunes115

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONIn this paper we would like to open a discussion on an innovative approach for sustainablegroundwater exploitation within nature reserves at dune sites, especially on islands of theEuropean North Sea. This contribution responds to the request made during the recent SaltWater Intrusion Meetings to discuss more ecology related issues in addition to the classictopics of modeling and geophysics.The water supply of the North Sea islands has relied in the past on the exploitation of thefreshwater lenses. As a result of an increasing demand during the last decades, salt waterintrusion has become a more severe problem. Geologists and engineers often succeed in theapplication of effective practices in the prevention of saltwater intrusion. These are sometimesinhibited by environmental protection interest groups. The ecologists’ concern is that criticalgroundwater-dependent ecosystems may be damaged by lowering of groundwater drawdown.The use of alternative water resources will multiply the price of tap water. The specificationof alternative water supply systems, e.g., desalination or long distance transport by pipelinesoften has decisive negative effects on the environment as well.About one hundred years ago, the North Sea islands became holiday destinations and anappropriate infrastructure was developed. During 2010, e.g., the island of Sylt with its 12,000inhabitants faced 6.6 million overnight stays and up to 100,000 day-trip visitors on a singleday. Tourists and related commercial activities result in decisive seasonal differences in waterdemand. Water demand is highest in July and August, and decreases towards autumn andwinter.Large areas of the islands’ landscapes are nature reserves protected by regional, federal,European and United Nations environmental legislation. This is especially true for the islandscovered by dunes. Habitats of the dune landscape are characterized by their local hydrologicalboundary conditions. From the head of a dune down to the dune slack, the amplitude of shorttimefluctuations of various parameters decreases. Aquatic plant associations cover the duneslacks. Areas where ponding occurs, e.g., Litorella uniflora association or fen-type plantcommunities may develop. These plant communities are classified in general as associationswhich continuously demand water level at ground surface or above. For survival soils have tobe wet during whole year with a special emphasis on spring for recovery, vegetation growthand reproduction. Not only flora demands ponding during spring; e.g., the natterjack toadspawns as soon as temperatures rise and water patches develop even in furrows. Within a fewweeks the spawn develops and after metamorphosis of polliwogs the animals leave theaquatic habitat.116

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives2 RESULTSOFINVESTIGATIONSWe monitored and investigated groundwater and surface water levels at several sitescharacterized by shifting sand dunes. The time series were extended by simulation ofgroundwater dynamics using a calibrated and validated numerical Feflow-model taking into1.90Groundwaterlevelanddrinkingwaterdemand12001.7010001.50]N[mad 1.30erhatew1.10dnuroG0.90800600400]thnom³/[mdanmerdateW0.702000.500naturalGroundwaterleveldrinkingwaterdemandFigure 1: Groundwater level and public water demand over a 9 years periodaccount density driven flow. The ecosystems on the islands of the Northsea develop under apronounced non- uniform hydrological balance. Following the seasonal pattern of rainfall andevapotranspiration significant groundwater recharge occurs only during autumn and wintermonths. This regime results in high groundwater tables from late autumn to spring, and lowwater levels during late spring and autumn. In summary, natural dynamics of groundwatertables and temporal regime of distribution of drinking water exhibit an opposite trend in thecourse of the year (fig. 1). The two sinusoidal curves differ from each other by the season ofmaximum groundwater levels.Hence the task to be solved is to balance sufficient groundwater extraction with negativeimpact on local ecosystems. Both aspects are assigned a high value also by legislation. Thisconflict often results in a limitation of groundwater exploitation. Commonly authoritiesrestrict groundwater extraction to a maximum draw down level. The threshold values areoften based on very general considerations. A more sophisticated approach is described byPetersen et al. 2003. The researchers recorded groundwater regime below different plant117

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivescommunities. They derived a threshold value (critical minimum) by calculating the medianbetween the mean groundwater level and the mean of the lowest three groundwater levels of aspecific time series. This critical minimum is defined as the threshold value, below whichplant communities will experience severe damage, when occurring regularly and for longperiods. Petersen et al. (2003) claim that water works should set up their exploitation schemetaking into account the critical minimum as threshold value for maximum draw down ofgroundwater table.1.90Groundwaterdynamicsataduneslack1.701.50]Nad[m1.30erhatewd1.10nuroG0.900.700.50naturalGroundwaterlevel simulatedextractionscenario Surfacelevel/criticalminimumFigure 2: Groundwater level, level of ground surface which equals critical minimum of plantassociation and calculated groundwater level of a extraction scenarioFigure 2 display groundwater level for a period of 10 years as well as the level of groundsurface. Mapping of flora and fauna was performed by a team of biologists. At the monitoringsite the identified plant association is characterized by a critical minimum of 0 cm. A criticalminimum of 0 cm means, that the whole soil profile should be continuously saturated bywater up to the surface. The times series of groundwater level reveals a pronouncedfluctuation down to 0.60 m below soil surface. In order to dissolve this contradiction furtherinvestigations are requested.When setting up the hydrogeological model the experts have taken into account a lesspermeable layer if the thickness was at least 0.2 m. The recorded soil profile exhibits a siltyand clayey layer between 2.60 m and 2.70 m below soil surface. With respect to the wholeisland this layer may not influence the overall hydrology, but the fine textured layer may118

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesattenuate the influence of rising and falling ground water table. The following components ofthe local soil hydrology contribute to ensure high soil humidity even during periods of lowgroundwater table:precipitation, dew, interception, evaporation, boundary layer, cover of soil, usable fieldcapacity, root zone, transpiration, capillary rise, water saturated and unsaturated lateral flow,hydraulic lift.3 RECOMMENDATIONSIn case investigations on salt water intrusion are part of an environmental impact study andgroundwater dependent ecosystems are located within the investigation area a detailed studyof the hydrology of the soil and the soil–plant-atmosphere-continuum should be obligatory.We propose here a dynamically adopted water extraction regime. The adoption should be tiedto meteorological and ecological constrains on one side and public water demand on the otherside.The flora and fauna need high soil humidity and open water surface during spring (e.g.,flowering, seed production, spawn, development of polliwog). Highest demand for drinkingwater covers July and August. In summer most years groundwater level is below criticalminimum, and most times below root zone of vegetation. During this period additionaldrawdown of the groundwater table will not inflict further damage to the ecosystem. Publicwater demand during winter season allows for an extraction scenario sufficiently low towarrant replenishment of the aquifer ensuring spring time water availability for flora andfauna. Application seems to be restricted to areas of sandy soils where a significant time lagbetween rainfall and groundwater recharge can not occur. Usually, restrictions imposed ongroundwater extraction by a sustainable use of the freshwater lense (preventing saltwaterintrusion) are partly coincidental with ecological requirements.To develop an appropriate extraction scenario, application of validated, density dependentgroundwater model is crucial. Output of the model may be used as boundary conditions forsoil water dynamics, which should be studied in detail. The concept of ‘critical minimum’may be refined and developed further. With respect to waterworks future studies should aimat an automatically controlled groundwater pumping based on a network of devices, whichautomatically measure, record and transmit, e.g., groundwater level and electric conductivitydata.Petersen, J., Pott, R., Janiesch, P. & Wolff, J., 2003. UmweltverträglicheGrundwasserbewirtschaftung in hydrogeologisch sensiblen Bereichen der Nordeseeküste.Husum Druck- und Verlagsgesellschaft.119

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesAPPLICATION OF ELETROKINETIC BARRIER FOR SALINE WATERINTRUSION: AN APPROACH FOR COASTAL AQUIFER MANAGEMENTIN MACEIÓ-AL.LIMA, Jonathan Tenório de; GUEDES Jr.; J. C.; SOUZA, M. M.; BARBOSA, M. C.jonathantenorio88@gmail.comCOPPE/UFRJCidade Universitária da UFRJ Ilha do Fundão - Rio de Janeiro - RJ - BrasilCaixa Postal 68506 CEP 21945-970Abstract. The process of salt water intrusion in coastal aquifers of Maceió has been seen as aserious challenge to urban environmental management. In particular there is anoverexploitation of groundwater for public and private water supply. According to Nobre andNobre (2001) about 80% of water supply is conceived from groundwater. The local geology isconstituted by sandstone sediments varying from fine to medium sands intercalated by claylenses that originate the geological formations Barreiras, Maceió and Coqueiro Ceco. Eliset.al. (2004) verified an increasing evolution on salt concentrations in groundwater, includingsites located close to supply wells. The problem is worsened due to the number of irregularwells not registered on the environmental agency in disagreement with grant instrument ofNational Water Resources Policy already in force all over country. As a mitigation of theenvironmental impact it is proposed to apply electrokinetic barriers. Eletrokinesis occurs dueto the presence of an electric field what induce ions to migrate in the direction of theelectrode of opposite charge. Then cations move to anode and anions move to cathode. Ingeneral free positive charges exceed the number of negative charges on soil surface and thena resultant flow take place in the direction of anode. The method has been demonstrated to besatisfactory for containment of heavy metal plumes (Lynch, 2007) and it is believed that thesame can be successfully used for salt water wedge. The tool is underutilized in Brazil,however it can represent an advance for solving this kind of problem. Elis, V. R.; Barroso,C.M.R.; Kiang, C.H. (2004). Aplicação de ensaios de resistividade na caracterização doSistema Aquífero Barreiras / Marituba em Maceió – AL. Rev. Bras. Geof. vol.22 no.2 SãoPaulo. Lynch, R. (2007). Electrokinetic Barriers for Preventing Groundwater Pollution. In:Reddy, K.; Cameselle, C. (editors). Electrochemical remediation technologies for pollutedsoils, sediments and groundwater, chapter 16, p. 335-356, New Jersey: John Wiley and Sons.Nobre, M.M.M.; Nobre, R.C.M. (2001). Nobre, M.M.M. Caracterização Hidrogeológica paraUso Racional e Proteção dos Mananciais Subterrâneos em Maceió-AL. RBRH-RevistaBrasileira de Recursos Hídricos, vol. 6, n.1, p.7-20.Keywords: eletrokinetic barrier; aquifer management; salt water intrusion120

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCLIMATE PROOF AREAS: INNOVATIVE SOLUTIONS FOR IMPROVINGTHE FRESHWATER AVAILABILITY!Van BAAREN, E. S.; De LOUW, P. G. B.; OUDE ESSINK, G. H. P.; PAUW, P.;HAREZLAK, V.esther.vanbaaren@deltares.nlDELTARESAbstract. The Dutch island Schouwen-Duiveland is surrounded by saline water, lies mainlybelow sea level and suffers drought and salt damage to crops. The island was selected by theEU projects CPA and Cliwat as pilot for climate related research. Implementation ofmeasures is often not successful due to a lack of technical knowledge or ‘forgetting’ thepractical knowledge and wishes by researchers. Can the combination of geohydrologicalresearch and workshops with farmers lead to the implementation of successful measures forfreshwater supply?; The current situation has been investigated with this approach. Theimpacts of climate change of the last decades are experienced by farmers: 10-30% droughtdamage to crops and inappropriate areas for agriculture due to salinisation. With acalibrated density dependent groundwater model the freshwater resources have beenlocalized and climate change has been quantified: salt loads from the groundwater systemwill increase with 20% within 40 years. Climate change is not part of farmers business, butthere is a common sense of urgency.; Concrete plans for innovative solutions to improve thefreshwater supply on the island were developed for 1. areas with limited fresh water availablefor irrigation and 2. saline seepage areas with thin rainwater lenses floating on saltgroundwater where irrigation is too expensive. Solutions lie in the geohydrological system:increasing freshwater lenses in creek ridges for irrigation and making the vulnerablerainwater lenses climate-robust. Field experiments together with the farmers start in 2012.;The combination of quantification instruments and practical experience created opportunitiesfor innovative countermeasures for an independent climate-robust freshwater supply. Thesense of urgency has been felt by the local government which resulted into their strategicvision for freshwater availability on the island. With successful field test, this approach canbe applied worldwide in vulnerable deltas.Keywords: freshwater, solutions, innovation, climate, island121

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHOW TO DETERMINE A ‘RELIABLE’ 3D FRESH-BRACKISH-SALINEDISTRIBUTION IN DATA-RICH COASTAL GROUNDWATER SYSTEMSOUDE ESSINK, G.; VAN BAAREN, E.; DE LOUW, P.; FANECA-SANCHEZ, M.Hgualbert.oudeessink@deltares.nlDELTARESPO Box 85467, 3508 AL Utrecht, The NetherlandsAbstract. In especially deltaic areas, groundwater systems often contain complex freshbrackish-salinedistributions. As groundwater flow is a slow phenomena, evenpaleohydrogeographical processes and anthropogenic activities of centuries ago still affectthe fresh-brackish-saline distribution in the system. The processes on different time scales,such as trans- and regressions during Holocene times, past sea level rise, differentiated landsubsidence, salt water wedges via surface water and excessive groundwater extractions areall affecting this distribution, and make it more diverse and complex. This fresh-brackishsalinedistribution is a important input in coastal groundwater studies to assess the impacts ofglobal (human) activities and climate change, but it is difficult to determine. The danger ofusing only one fresh-saline interface is considered, in fact: only one interface is rather poorin handling future fresh water demands. In this paper we discuss one specific procedure tocreate a reliable 3D fresh-brackish-saline distribution in a data-rich coastal groundwatersystem. The study area is in the Province of Zeeland, The Netherlands, which possesses anenormous amount of geophysical and hydrological data. It is a complex setting with quickpaleohydrogeographical changes which (partly) cause the rough salinity pattern. Numeroustypes of data, such as samples (since 1850), VES, Borehole data, CPT, EM31, TEC, etc arecombined with an estimated fresh-brackish interface. Samples will show trends of salinisationand freshening; unfortunately, the samples are more reliable than VES but often lesscommon. Ultimately, a numerical 3D variable density groundwater flow and coupled solutetransport model is used to significantly improve the 3D fresh-brackish-saline distribution, aswe believe a model is a good interpolator to create optimal distribution. Verification andcalibration with (other) geophysical data (o.a. Airborne HEM) will be shown to quantify thematch between field and model, and the capacity to predict trends in samples will bediscussed.Keywords: deltaic areas, procedure, 3D fresh-brackish-saline distribution, geophysics,modelling122

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGAINING THE NECESSARY GEOLOGIC, HYDROLOGIC, AND GEOCHEMICALUNDERSTANDING FOR ADDITIONAL BRACKISH GROUNDWATERDEVELOPMENT, COASTAL SAN DIEGO, CALIFORNIA, USADanskin, Wesley R.wdanskin@usgs.govUnited States Geological Survey4165 Spruance Road, Suite 200, San Diego, CA, 92101, USAAbstract. Local water agencies and the United States Geological Survey are using acombination of techniques to better understand the scant freshwater resources and the muchmore abundant brackish resources in coastal San Diego, California, USA. Techniques includeinstallation of multiple-depth monitoring well sites; geologic and paleontological analysis ofdrill cuttings; geophysical logging to identify formations and possible seawater intrusion;sampling of pore-water obtained from cores; analysis of chemical constituents including traceelements and isotopes; and use of scoping models including a three-dimensional geologicframework model, rainfall-runoff model, regional groundwater flow model, and coastaldensity-dependent groundwater flow model. Results show that most fresh groundwater wasrecharged during the last glacial period and that the coastal aquifer has had recurringintrusions of fresh and saline water. These intrusions disguise the source, flowpaths, andhistory of ground water near the coast. The flow system includes a freshwater lens resting onbrackish water; a 100-meter-thick flowtube of freshwater discharging under brackishestuarine water and above highly saline water; and broad areas of fine-grained coastalsediment filled with fairly uniform brackish water. Stable isotopes of hydrogen and oxygenindicate the recharged water flows through many kilometers of fractured crystalline rockbefore entering the narrow coastal aquifer.Keywords: Brackish groundwater, monitoring wells, geochemistry, models, management123

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONCoastal hydrogeologic systems, particularly in areas of modest rainfall, runoff, and recharge,are complex and difficult to decipher. The primary forcing function of less precipitationresults in less erosion, smaller aquifers, slower groundwater flowrates, and a predominance ofbrackish groundwater. The coastal area of San Diego, California, USA, is such a setting wherewater managers are challenged by the scant local water supplies, and by an increasingpopulation (fig. 1).Figure 1. Study area of coastal San Diego County, California, USA.Moderately permeable sedimentary formations, mostly of Pliocene and Eocene age, form anarrow coastal aquifer extending from coastal reservoirs to the Pacific Ocean (fig. 1). Furthereast, where most of the recharge occurs, weathered and fractured granitic and metavolcanicrocks form the more extensive, but less permeable hardrock aquifer. Most of the coastal plainis underlain with brackish (2,000 parts per million dissolved solids) groundwater.2. METHODSLocal water agencies and the United States Geological Survey (USGS) are using acombination of techniques to provide the necessary understanding of the geology, hydrology,and geochemistry to develop the scant freshwater resources and the much more abundant124

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesbrackish resources. The techniques include installation of twelve 500-meter-deep multipledepthmonitoring well sites, each with 4 to 6 piezometers equipped with pressure-recordingtransducers (fig. 1). These water-level data are uploaded to the USGS database and linked tothe project webpage [http://ca.water.usgs.gov/sandiego] to aid in realtime water management.The well sites are located in east-west pairs (e.g. SDSW–SDMC, fig. 1), aligned with thegeneral direction of groundwater flow and positioned along drainages to monitor streamaquiferinteraction. The eastern well monitors existing well fields (Danskin and Church,2005); the western well is a sentry to detect seawater intrusion (Cronquist and others, 2011).During installation of the well sites, drill cuttings are collected and analyzed for color, grainsize,provenance, and paleontological indicators of age and depositional environment.Geophysical logs are obtained to identify formations and depths of saline water. Cores arecollected and analyzed for hydraulic characteristics, and for optical thermal luminance andpaleomagnetic reversals to indicate age since deposition. These data are combined to create athree-dimensional geologic framework model (fig. 2).Figure 2. Fence diagram created from the USGS geologic framework model. Six layersinclude crystalline rock (purple), Cretaceous rock (green), Eocene sediment (tan), Oligocenesediment (orange), Pliocene San Diego Formation (blue), and Quaternary sediment (yellow).Multiple-depth well sites form vertices of the fence diagram.125

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGeochemical analysis includes samples of pore-water squeezed from cores, and subsequentsampling of the piezometers for a broad range of chemical constituents including traceelements and isotopes. Stable isotopes of hydrogen and oxygen are used to identify the likelyarea of recharge. Major ions and strontium isotopes are used to identify possible groundwaterflowpaths (Anders and Futa, 2010).A suite of numerical models is used to integrate data and to test ideas about geologic structureand arrangement of formations, location and quantity of recharge, quantity and flowpaths ofgroundwater, interaction of surface water and groundwater, configuration of fresh and salinewater, and possible areas to extract additional brackish groundwater. These numerical modelsinclude a three-dimensional geologic framework model using RockWorks TM and EarthVision Rsoftware (Glockhoff, 2011; fig. 2), a rainfall-runoff model using the BCM method (Flint andFlint, 2007), a regional groundwater flow model using the USGS MODFLOW code, and acoastal density-dependent groundwater flow model using the USGS SUTRA code.3. RESULTSResults of the investigation show that most of the fresh water was recharged during the lastglacial period, and that the coastal aquifer has had recurring intrusions of fresh and salinewater (Cronquist and others, 2011; fig. 3).Figure 3. Electromagnetic logging at the SDNB well site (fig. 1) measures changes in salinitywith depth from 2006 to 2011. Data show an upper zone of saline intrusion (0-600), a middlezone of freshwater intrusion (600-1000), and a lower zone of highly saline water (1000-1500).126

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesThese intrusions disguise the source, flowpaths, and history of groundwater near the coast.Complexity of the groundwater flow system includes a relatively small area with a freshwaterlens resting on brackish water; a 100-meter-thick flowtube of freshwater discharging underbrackish estuarine water and above highly saline water (fig. 3); and broad areas of finegrainedcoastal sediment filled with fairly uniform brackish water.Stable isotopes of hydrogen and oxygen identify the likely areas of the recharge, more than 20km east and upgradient from the semiarid coastline (Anders and Futa, 2010; Wright andothers, 2011). Chemical data indicate the recharged water flows through many kilometers offractured crystalline rock before it enters the narrow sedimentary coastal aquifer.The management challenge of increasing municipal supply is to capture more of the freshgroundwater on its way to the ocean and extract some of the brackish groundwater fortreatment using reverse osmosis. The deep multiple-depth well sites are being used tocharacterize the geologic, hydrologic, and geochemical systems and to monitor seawaterintrusion, land deformation, and effects on coastal riparian systems.REFERENCESAnders, Robert and Futa, Kyoto, 2010, Determination of groundwater flow paths in a coastalSouthern California aquifer: H43A–1208, AGU fall meeting, San Francisco, California,December 13–17, 2010 [poster].Cronquist, D.A., Banister, S.D., and Anders, Robert, 2011, Delineating Zones of SeawaterIntrusion in a Coastal Southern California Aquifer: H31G–1249, AGU fall meeting, SanFrancisco, California, December 5–9, 2011 [poster].Danskin, W.R., and Church, C.D., 2005, Determining age and vertical contribution of groundwater pumped from wells in a small coastal river basin. A case study in the SweetwaterRiver Valley, San Diego County, California: U.S. Geological Survey, Open-File Report2005-1032, 4 p.Flint, A. L., and Flint, L. E., 2007, Application of the Basin Characterization Model toestimate in-place recharge and runoff potential in the Basin and Range carbonate-rockaquifer system, White Pine County, Nevada, and adjacent areas in Nevada and Utah: U. S.Geological Survey Scientific Investigations Report 2007–5099, 18 p.Glockoff, C.S., 2011, Mapping the San Diego Underground: ESRI International UserConference, July 11–15, 2010 [poster].Wright, M.T., Belitz, Kenneth, and Burton, C.A., 2004, California GAMA program: Groundwaterquality data in the San Diego drainages hydrogeologic province, California: U.S.Geological Survey, Data Series 06–129, 91 p.Brand names are for identification purposes only and do not imply endorsement by the USGS.127

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesyDRY FEET OR DRINKING WATER? RESOLUTION OF THE CONFLICT BETWEENCOASTAL DEFENCE AND DRINKING WATER SUPPLYM. Hoogmoed MSc. 1 ; Drs. J.T. Buma 2 ; R. Caljé MSc. 3 ’; Drs. G.J. Sissingh-Meijer 4m.hoogmoed@dunea.nl1 Dunea drinking water supply company; 2 Deltares; 3 Artesia Water; 4 MovaresPostbus 34, 2270 AA Voorburg, The NetherlandsAbstract. Dry feet or drinking water? Of course we want (and need) both! So how can it bethat one of the world’s biggest and most innovative coastal defence projects turned out to bein potential conflict with drinking water supply? At first thought no one imagined there to bean issue. But unexpectedly combining these two basic needs of life turned out to be aninteresting challenge. Without hydrological intervention, the drinking water production in theDunea dune area would no longer have been sustainable due to the effects of two coastaldefence projects.This paper will give insight in the challenges faced to protect the drinking water supplyagainst salt water intrusion and groundwater pollution by presenting field research andgroundwater model results. A study combining both resulted in the design of a system of 28interception wells on top of the dunes. Since the morphology of the coast is very dynamichere, the measure is demanded to be very flexible to enable mitigation of negative effects ofthe coastal defence projects now and in the future. The accompanying monitoring planfocuses on both the effectiveness of the system and ‘unexpected’ effects.Since sea levels are expected to rise in the future, coastal defence projects will play anincreasingly important role in coming decades. The insights presented in this paper mighthelp you to face what can be your challenge in the near future.Keywords: Salt water intrusion, Coastal defence, Monitoring, Remediation, Drinking water supply1. INTRODUCTIONSince 1887, Dunea produces high quality drinking water using the dune area at Monster(Province of South Holland, the Netherlands). Annually, 8 billion litres of water is producedhere using artificial recharge and recovery with shallow wells and infiltration lakes. Thedunes are an important step in producing drinking water serving as an underground buffer,levelling fluctuating in temperature and quality and removing bacteria and viruses from theinfiltrated water in a natural way.Since space is limited in the Netherlands, the drinking water production of Dunea is closelymatched with surrounding land uses and natural constraints. This prevents groundwaternuisance, upconing and intrusion of salt water and in this case also movement of a nearbygroundwater pollution. This is especially true in Solleveld where the dunes are fairly low andsmall; the coast is less then 350 metres from the recovery wells (Figure 1).128

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesyFigure 1a: Aerial photo of Solleveld, one of Duneas infiltration and recovery areas. Infiltration lakes andrecovery wells are shown. Figure 1b: Aerial photo showing the dimensions of the sand engine. (BingMaps)The coast of Monster was identified as a weak link in the coastal defence of The Netherlands.Because of this, two coastal defence projects were carried out between 2009 and 2011. Thefirst project involved creating an extra dune ridge in front of existing dunes. This lead tointrusion of a large volume of seawater (Figure 2a). Directly after completion, the SandEngine was constructed (Figure 1b and 2b). This hook shaped sand peninsula will supply thecoast with sand for the coming decades due to erosion and deposition along the coast.Figure 2a: ‘Rain bowing’ sand and sea water onto the coast of Solleveld in 2009 and 2010.Figure 2b: Sand Engine in front of the coast of Solleveld, (size: is 1.5km into the sea and 2km along the coast).2. RESULTS AND SOLUTIONSThese two large coastal defence projects would obviously influence the tightly balancedhydrological system of Solleveld. Without hydrological intervention, the drinking waterproduction would no longer be sustainable in this area. To study the effects of these projectsand so find a solution to combine coastal defence and drinking water supply, field researchand effect modelling were used interactively. The results are described below.129

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesy2.1 Field researchIn 2009, a field research was set up to monitor the effects of the coastal defence projects,especially the salt water intrusion, using different methodologies (focussed on both qualityand groundwater levels). The results formed an important input to the effect models(described below).Figure 3a shows the effects of the coastal defence projects on groundwater levels. The firstcoastal defence project resulted in a groundwater level rise of 5 metres in the dunes withindays. The pulse delayed and decreased while moving inland but was still almost 0.5 metre ata distance of 500 metres. These effects were temporary, although the depletion of the pulsetook around a month. The effect of building the Sand Engine in 2011 was much smaller;groundwater levels rose 20 centimetres in the coastal dunes (Hoogmoed, 2011). These effectswere only temporary. Models were used to determine the long term effects (Paragraph 2.2).Figure 3a: Groundwater level fluctuations due to coastal defence projects. Figure 3b Results of cone penetrationtests shown on aerial map (red and light blue are resp salt and fresh groundwater, dark blue is unsaturated.Also, cone penetration tests (CPT) were done after finishing the first coastal defence project.The results are shown in Figure 3b (DHV et al., 2010). Combining these results with thechemical signature of groundwater samples indicated that the salt water intrusion moved landinward between 25 and 100 metres (middle and southern cross section). The difference iscaused due to the shorter period between completion of the project and the measurements.2.2 Protecting the drinking water supplyThe field data was used to calibrate groundwater models which were then used to determinethe effects of the coastal defence projects (Artesia, 2011). It was generally concluded that thecombined projects would result in a seaward shift of the groundwater divide, which would intime lead to salinization of Duneas abstraction wells and land inward movement of apreviously controlled pollution plume (Figure 4a, left).In a study by DHV et al. (2010), different options for controlling or mitigating thehydrological effects were studied. From a hydrological point of view, creation of an extrainfiltration pond between the production area of Dunea and the dunes (with a water level130

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesyhigher than the average high tide sea level) was the preferred option due to its effectivenessand technical simplicity. This was however not possible because Solleveld is a protectednature conservation area. An equally effective (but technically more demanding) solution wasthe construction of interception wells on top of the new dune ridge (28 in total). Figure4a(right) and b show model results regarding the effectiveness of this measure.Figure 4a: result of 2D-model on the left: salinization of abstraction well (circle) if no measure is taken, on theright: interception well prevents salinization of wells. Figure 4b: Streamlines visualize salt water intrusion andthe effectiveness of the interception wells (shown as dots near the sea). (Source: Artesia, 2011)An important uncertainty is the size and location of the Sand Engine in time, since it is built toerode and deposit along the coast. Morphological models have been made on the behaviourof the Sand Engine, but recent data (2012) already show a different behaviour than predicted.Therefore, operation of the interception system must be flexible enabling mitigation ofnegative effects of the coastal defence projects now and under future coastal dynamics. Theaccompanying (dynamic) monitoring plan plays an important role regarding this (Buma etal., 2012). It focuses on the effectiveness of the interception wells, but also on effects causedby unexpected behaviour of the system. Together, the interception system and monitoring planare expected to guarantee further sustainable use of the dunes of Solleveld for drinking waterproduction, as it was for over a hundred years before.REFERENCESArtesia Water (2011). Resultaten instationaire modelberekeningen beheersmaatregel. Artesia WaterB.V. (In Dutch only)Buma J.T., Hoogmoed M., Sissingh-Meijer G. (2012). Monitoringplan grondwater Solleveld enfunctioneren beheersmaatregel. Deltares. (In Dutch only)DHV and Artesia (2010). Beheersmaatregelen Delflandse Kust/Zandmotor/Dunea. DHV AC8545. (InDutch only)Hoogmoed M. (2011). Effectanalyse van Zandmotor en Kustversterking op duingebied Solleveld –managementsamenvatting. Dunea. (In Dutch only)131

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesEFFECTS OF NATURAL RECHARGE AND IRRIGATION ONGROUNDWATER SALINITY IN A COASTAL UNCONFINED AQUIFER,LIDO DI DANTE, RAVENNA, ITALY.GREGGIO, Nicolas; MOLLEMA, P.;ANTONELLINI, M.; CAPO, D.;GABBIANELLI, G.pmollema@gmail.comUNIVERSITY OF BOLOGNAVia san Alberto 163, Ravenna, Italy.Abstract. Around Ravenna (Italy), more than 6800 hectares are at risk for soil salinization.This is agricultural land near sea level. We have studied a 10km-long transect, perpendicularto the Adriatic coast. A quarterly hydrologic monitoring was conducted during 2010-2011 inten wells for water table height, salinity of the groundwater and hydrochemical analysis. Adetailed study was carried out on a small agricultural area (10ha), at 500m from sea, arounda ditch which is filled with freshwater in summer to irrigate the nearby fields. Thickness anddimensions of the freshwater lens near this irrigation channel was studied with VES, inMarch and July of 2010. The scope of this study is to quantify the effect of irrigation on thesalinity of the groundwater and to assess whether irrigation practices can help to counteractfurther groundwater and soil salinization. The hydrochemical analysis shows that the coastalaquifer contains brackish/salt Na-Cl type water up to 7 km from sea; with some fresh water atthe top of the aquifer underneath the pine forest and near the gravel quarries and in the areaof detailed study. Near the irrigation ditch the water type is Ca-HCO3 similar to river water.Rainfall from January to September 2011 was 400 mm while total irrigation of a tomato fieldwas 600 mm, applied with a rate of 120 mm per month (April-August 2011). The infiltrationrate of water into the aquifer, measured from drain gauges was 8 mm/m2 in May, 2 mm/m2 inJune and 0 mm/m2 in the other months. In winter the water level in the irrigation channel isequal to the groundwater level but during growing season it creates a hydraulic gradienttowards sea. Comparing the V.E.S. profiles from different seasons confirms that the freshwater lens increases in size during the irrigation season. This study shows that infiltration ofexcess irrigation water occurs only via the irrigation ditch and not from superficial irrigation.Keywords: salt water intrusion, coastal aquifer, recharge, irrigation, infiltration,Mediterranean132

GROUNDWATER ARTIFICIAL RECHARGE IN DAR ES SALAAM COASTALAQUIFER: A STRATEGY FOR MANAGING SEAWATER INTRUSIONMTONI, Yohana 1, 2 ; MJEMAH, Ibrahimu Chikira 3 ; WALRAEVENS, Kristine 1 Keywords: 133

1. INTRODUCTION 134

2. GEOLOGICAL SETTING 3. HYDROGEOLOGIC SUITABILITY AND NATURAL RECHARGE 4. ARTIFICIAL GROUNDWATER RECHARGE135

5. ARTIFICIAL RECHARGING TECHNIQUES6. CONCLUSION AND FURTHER RESEARCH NEEDSREFERENCES136

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesINFLUENCE OF SEAWATER INTRUSION ON WATER QUALITY: A CASESTUDY FROM INDIASHARMA, S.K.sks105@rediffmail.comCARMAN RESIDENTIAL AND DAY SCHOOLShyampur, Dehradun 248007, IndiaAbstract. Water quality plays an important role in promoting agricultural production andstandard of human health. Salinization due to sea water intrusion impacts the water resourcesin parts of Krishna-Godavari Basin of Andhra Pradesh on the eastern coast of India. Anumber of bore wells have been drilled for the abstraction of water for irrigation anddrinking purposes. Salinity hazards have occurred due to sea water intrusion as the aquifersare open to the sea, entrap sea water in the sediments and seawater intrusions through tidalcracks. Indiscriminate pumping has resulted in groundwater overexploitation and sea waterintrusion with salinization of aquifers and landward movement of saline water – freshwaterinterface for several kilometres in this Basin. In several parts, the bore wells are found toyield saline / brackish water due to seawater intrusion. The groundwater is mostly of brackishtype, having Na+ : Cl- facies. The TDS (1912/ 2258 mg/l),TH (365/393mg/l), Na+ ( 721/ 739mg/l), Cl– (781/ 869 mg/l), SO4- - (122/ 93 mg/l) and F-(1.6/1.9 mg/l) concentrations are inexcess of the safe limit in accordance with the domestic and industrial water quality standardof WHO. Excessive amounts of fluoride (more than 1.5 mg/l) in drinking water is found to betoxic. The basic problem of groundwater management of the region is its development withoutdisturbing the saltwater / freshwater interface. This may be achieved by limiting thegroundwater abstraction through enactment of groundwater legislation and recharging theaquifer artificially by rainwater.Keywords: aquifer; brackish; fluorosis; groundwater; irrigation137

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMODELLING AS(T)R IN THE AMSTERDAM WATER SUPPLY DUNES TOEXPLORE OPTIONS TO COPE WITH FUTURE INTAKE WATERSHORTAGES CAUSED BY CLIMATE CHANGENIENHUIS, Philip; OLSTHOORN, Theophilip.nienhuis@waternet.nlWATERNETWaternet, P.O. Box 94370, 1090 GJ Amsterdam, The NetherlandsAbstract. In the Amsterdam Water Supply Dunes (AWD) pre-purified Rhine water isinfiltrated in the shallow (phreatic) aquifer to recharge the groundwater system from whichAmsterdam is supplied with drinking water. It is expected that future climate change will leadto lower summer discharges of the Rhine river, to the extent that in extreme low-flow periodsthe water quality might be unfavourable for intake, and perhaps even not available at all. It isexpected that during high-flow periods the Rhine water quality will be preferrable because ofmuch higher dilution rates of possible pollutants. So, extra intake and infiltration of goodquality Rhine water in the AWD during high flow periods, followed by extraction in low-flowperiods, might help to get an overall better groundwater quality in the AWD and could be asolution for Rhine water intake interruptions. As the AWD forms an important nature reserve,surficial storage or storage in the shallow (phreatic) aquifer is not acceptable for prolongedperiods. Therefore, a solution is sought in the form of AS(T)R in the fresh-water lens belowthe AWD. A pre-feasibility study has been undertaken to explore possible effects of a“breathing” fresh-water lens. The main objective of this study has been to assess feasiblemagnitudes of storage from a geohydrological perspective. Effects on hydrogeochemistryhave been studied separately. Rough initial calculations suggest a vertical migration of thesaline/fresh groundwater interface in the order of one meter per Mm3 artificial injection ofRhine water, and vice versa during extraction, implying intense mixing around thesaline/fresh interface. Therefore, in this stage emphasis was put on the main challenges, viz.how to control the generation and subsequent migration of brackish groundwater;countermeasures against expected upconing of saline groundwater during extraction of thegroundwater reserve; and possible adverse hydraulic effects on neighbouring areas. Invokingthe 3D unsteady state groundwater model of the AWD (AMWADU) for all scenarios wouldrequire undue resources and time; in addition it is based on the SWI package so it cannot aidin estimating the amounts of generated brackish groundwater. To overcome these hurdles anumber of 2D cross-sectional groundwater models have been extracted from AMWADU. Inthese cross-sections, several unsteady state AS(T)R scenarios could be simulated inreasonable time with SEAWAT, driven by the “mfLab” interface (Olsthoorn, 2010). Theresults show that seasonal storage (required storage ~ 20 Mm3/yr) is unfeasible, but smallerstorage magnitudes, and thus shorter periods of interrupted intake of Rhine water, have ahigher chance of being accommodated successfully. The current drinking water productionsystem is based on surface water (canals) for groundwater recovery, storage and transportand as such it is vulnerable for among others, re-infection and pollution. As a consequence itrequires extensive and expensive post-purification. Therefore, an especially interesting aspectis how the studied AS(T)R system might be incorporated at a later stage into a full-scaleASTR system that could replace the current surface water infiltration and recovery system,thus mitigating risks for deteriorating water quality after recovery and allowing downscaling138

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesof the presently required post-purification. A future “closed” recovery system could comprisea steady-state ASTR system (water balance close to zero) on which oscillatinginjection/extraction cycles are superposed in time. Depending on the actual location ofinjection and recovery wells, the steady-state AS(T)R system could be a big help incontrolling the generated brackish groundwater zone and keeping it away from the extractionwells.Keywords: ASR Climate-change mflab dune upconing139

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMULTILEVEL CHARACTERIZATION OF VERTICAL HYDRAULIC GRADIENTS,PERMEABILITY, TEMPERATURE AND SALINITY IN SHALLOW COASTALAQUIFERS WITH LOW PRESSURE PACKERSBeatrice M.S. Giambastiani 1 ; Nicolò Colombani 1,2 ; Micòl Mastrocicco 1gmbbrc@unife.it1- Earth Sciences Department, University of Ferrara (Italy)Via Saragat 1, 44122 Ferrara (Italy)2- Interdepartmental Center of Environmental Sciences (CIRSA), University ofBologna (Italy)Abstract. In this study we tested the ability of straddle low pressure packers to characterizesimultaneously vertical hydraulic gradients, permeability, temperature and salinity in orderto quantify the magnitude and direction of groundwater fluxes and understand salinizationprocesses in coastal aquifers. The straddle packers are employed to isolate a window of 0.2 mwithin fully penetrating piezometers. The system is set at the desired depth within thepiezometer and a constant rate pumping test is performed. A Levelogger is positionedbetween the packers to monitor head, temperature and electrical conductivity, from which theequivalent freshwater head and intrinsic permeability values can be derived. Two piezometerslocated in a coastal aquifer of Ferrara Province (Italy) have been characterized using thistechnique. In addition core samples from the same piezometers have been analysed for grainsize, porosity and organic matter. The laboratory data are used to compare the resultsobtained using the packers system with intrinsic permeability calculated by pedotransferformulas. The comparison of the two techniques shows a general agreement along eachpiezometer profile, although discrepancies of more than 1 order of magnitude occur in peatylayers. The multilevel equivalent freshwater heads highlight a steep vertical gradient createdby the drainage system. This seepage is contrasted by lenses of silt and clay that prevent thecomplete salinization of the shallow aquifer.Keywords: Intrinsic permeability, Pumping test, Salinization, Seepage, Straddle packers140

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONA sustainable management of the coastal aquifers needs to quantify the magnitude anddirection of groundwater fluxes. This task is usually achieved by characterizing the physicalproperties of the hydrogeological units, their spatial heterogeneity and their connection withsurface water bodies. One of the key issues to understand salinization processes in a coastalaquifer is the vertical variability of aquifer properties, like the permeability, since seawater ischaracterized by elevated density and viscosity with respect to freshwater and this featureinduces density driven flow within coastal aquifers (Barlow 2003). For these reasons there isthe need of time-effective techniques to quantify groundwater fluxes in salinized aquifers.2. MATERIALS AND METHODIn this study we present the ability of straddle low pressure packers to characterizesimultaneously vertical hydraulic gradient, permeability, temperature and salinity. Thestraddle packers are employed to isolate a window of 0.2 m within fully penetratingpiezometers. Between the packers a Levelogger LTC Solinst is positioned to monitor, everysecond, the head, temperature and electrical conductivity within the sampling window. Thesystem is set at the desired depth within the piezometer and a constant rate pumping test isperformed using a centrifuge pump and a flow controller. Before to start the pumping test, theinflated packers system is left to stand until the piezometric equilibrium is reached and thepoint head measurement is recorded.Hydraulic conductivity values (K) (m/s) are derived from the equation (Bureau ofReclamation, 2001):QK = (1)Csr∆hwhere Cs (-) is the conductivity coefficient for semi-spherical flow in saturated materialsthrough partially penetrating cylindrical test wells (equal to 28 in these conditions), r (m) isthe radius of the test well, h (-) is the hydraulic gradient between static head and steadystate head under pumping condition.Since the Levelogger acquires simultaneously the piezometric drawdown induced by pumpingand any variation in the temperature and electrical conductivity within the aquifer windowisolated by the packers, the equivalent freshwater head (h f ) and intrinsic permeability ()values can be derived using the following equations (Post et al., 2007; Fetter, 2004).ρhf= h(2)ρfwhere and f (kg/m 3 ) are the density of the point-sampled water and fresh water,respectively; andµκ = K (3)ρ gwhere (Kg/m s) is the dynamic viscosity and g (m/s 2 ) is the acceleration due to gravity.141

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTwo piezometers located along a flow line in a coastal aquifer of Ferrara Province (Italy)have been characterized using this technique. This coastal area is reclaimed land,topographically depressed below the sea level (Mastrocicco et al., 2012). The 2” piezometersare fully screened with a geotextile sock instead of gravel pack to prevent short-circuitsduring the pumping tests. In addition core samples from the same piezometers have beenanalysed for grain size, porosity and organic matter. The laboratory data are used tocompare the results obtained using the packers system with intrinsic permeability calculatedby pedotransfer formulas, such as Terzaghi, Breyer and Shepherd formula (Vukovic and Soro,1992).3. RESULTS AND DISCUSSIONSFig.1 – Freshwater head and seepage (left plots a and c), hydraulic conductivity and electrical conductivity(right plots b and d) values within two piezometers. Note that negative seepage means flux from the bottomtoward the surface, while positive values indicate downward flux.The multilevel equivalent freshwater heads and seepage values (Fig. 1a,c) highlight upwardvertical fluxes (up to 10 m/d) created by the drainage system, which forces groundwater toflow upward. In some cases this upward flux is contrasted by lenses of silt and clay that limitthe seepage and prevent the complete salinization of the shallow aquifer. This feature is veryimportant since the reclaimed land is mainly used for agricultural purposes and soilsalinization could cause severe problems to crops sensitive to salinity stress. The hydraulicconductivity decreases from 10 -4 to 10 -6 m/s from the top to the bottom of the aquifer (Fig.1b,d). Electrical conductivity values show high salinity in the entire coastal aquifer (Fig. 1142

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesb,d); freshwater lenses only occur in the shallow part of the aquifer where sand units(palaeodunes) permit rainfall recharge and infiltration (positive seepage in Fig 1a).The comparison between hydraulic conductivity values derived by equation 1 and thosedetermined by pedotransfer formulae based on grain-size analysis, shows a generalagreement along each piezometer profile. Although, the best linear fit between pedotransferformulae (Breyer) and measured k values gives a R 2 of only 0.67. This low correlation ismostly due to the peaty sediments, where discrepancies of more than 1 order of magnitudeoccur since grain size characterization is particularly challenging due to the organic natureof these sediments. In addition, it has to be considered that the applicability of these formulaedepends on the type of sediment for which hydraulic conductivity has to be estimated. Vukovicand Soro (1992) noted that the applications of different empirical formulae to the sameporous medium material can yield different values of hydraulic conductivity, which may differby a factor of 10 or even 20.4. CONCLUSIONSThe proposed methodology is a cost- and time-effective technique relevant for a detailedcharacterization of coastal aquifer parameters and flow dynamics. Intrinsic permeability andmultilevel equivalent freshwater heads can be easily calculated from acquired data andvertical gradient in the aquifer can be highlighted. Despite of this, it must be remembered thathydraulic gradients can be accurately recognized only when at least decimetric differences inhead are present within a piezometer, due to the accuracy of pressure transducer.REFERENCESBarlow, P.M., 2003. Ground water in fresh water-salt water environments of the AtlanticCoast. U.S.G.S. circular, n. 1262.Bureau of Reclamation, 2001. Water testing of permeability. In: Engineering Geology FieldManual, vol. 2, Chap. 17, U.S. Department of the Interior, Washington, pp. 443.Fetter C.W., 2004. Applied Hydrogeology. 4 th ed. Prentice Hall.Mastrocicco, M., Giambastiani, B.M.S., Severi, P., Colombani, N., 2012. The importance ofdata acquisition techniques in saltwater intrusion monitoring. Accepted in Water ResourcesManagement. Reference number: WARM2497Post, V., Kooi, H., Simmons, C., 2007. Using hydraulic head measurements in variabledensityground water flow analyses. Ground Water, vol., 45, n. 6., pp. 664-671.Vukovic, M., Soro, A., 1992. Determination of hydraulic conductivity of porous media fromgrain-size composition. Water Resources Publications Littleton, Colorado143

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PRELIMINARY EVALUATION OF SALINE INTRUSION AND SALINITY IN THEMUNICIPALITY OF GROUNDWATER QUISSAMÃ - RJ, BRAZIL Abstract. 148

1. INTRODUCTION 2. MATERIALS AND METHODS 3. RESULTS3.1 Results of the field survey . 149

3.2 Laboratory results 3.3 Map isovalores electrical conductivity 150

4. CONCLUSIONS 151

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSALINITY RISK GROUNDWATER ANALYSIS IN RIO DE JANEIRO STATENORTHERN REGION RJ-BRAZILMaria da Gloria Alves 1 ; Zélia Maria Peixoto Chrispim 1 ; Gerson Cardoso da Silva Júnior 2 ;Cláudio Limeira Melo 2 ; Egmont Capucci 3 ; Aderson Marques Martins 2Hmgloria@uenf.br1Universidade Estadual Norte Fluminense Darcy Ribeiro; 2 Universidade Federal Rio deJaneiro; 3 CEDAE -RJAv. Alberto Lamengo nº2000, Parque Califórnia – Campos dos Goytacazes /RJ CEP: 28013-600Abstract. The present study area comprises the towns of Campos, San Francisco and SãoJoão, which are part of the sedimentary basin of Campos, in Rio de Janeiro State,Brazil, and have deep wells in the coast. The increased demand for water supply in theregion, for installation of new industrial centers, expansion of agricultural practices andpopulation consumption leads to search for supply alternatives. The present study aims toinvestigate the risk of salinity in groundwater from deep wells. The methodology consisted inrecollection of water in 16 wells for physical and chemical analyses, salinity andsalinity risk classification using a software from United States Salinity Laboratory (USSL) .The classification of salinity ranges from freshwater (10 samples) to brackish water (6samples) with values varying from 159.9 mg / L to 1038.7 mg/L. The risk of salinity ingroundwater ranged from high (6 samples), medium (9 samples) to low (1 sample). The wellsthat were classified as brackish, with a high risk of salinity, correspond to differentaquifers in the region. According to the results of this survey, we conclude that groundwaterfrom deep wells is beyond acceptable standards for human consumption in some wells,without a specific pattern detected. There must be a monitoring of these wells in order toperform a proper management of these resources so important to the region.Keywords: Salinity Risk; Groundwater; Campos Basin1. INTRODUCTIONThe State of Rio has considerable groundwater resources in its sedimentary basins,and the Campos Basin has the greatest potential of the state. The present study areacomprises the area of Campos dos Goytacazes, Itabapoana of San Francisco and São Joãoda Barra towns (Figure 1), which are located on the terrestrial portion of Campossedimentary basin with deep wells in their entire coast. The region is located approximately279 km from t h e state capital, Rio de Janeiro. Campos is the largest city of the State,with an area of 4037 km 2 and a population of 434,008 inhabitants (IBGE 2009). Theincreased demand for water supply in the Region c o m e s f r o m both a rapid industrialgrowth due to an oil industry boom, and the expansion of agricultural practices andpopulation level of consumption. It leads to a search for alternatives to the water supply.The water abstraction through shallow and deep wells has been rapidly increasing in thepast few years. Thus, it is necessary to know appropriately the chemical and hydrodynamiccharacteristics of these waters, since the local coastal aquifers represent the greatestgroundwater potential in the State of Rio de Janeiro, though it is poorly studied until thepresent days.152

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGroundwater is of fundamental importance to the population in the region, since the existentsupply system, coming from the Rio Paraiba do Sul water treatment plants, do notmeet the entire population needs. Some authors have conducted studies on the groundwaterpotential in the Campos Basin (Caetano, 2000; CPRM, 2001; Capucci, 2003; Martins et al.2006). The unconfined aquifers are represented by Barreiras Formation and Quaternarysediments. As for the deep aquifers, there are different interpretations. According toCaetano (2000) and CPRM (2001), the region has a large sedimentary aquifer systemcomposed of Tertiary and Quaternary sediments: Fluvio-deltaic, Barreiras, Emborê, SãoTome I and São Tome II Aquifers. Despite the sedimentary aquifers of the onshore portion ofthe Campos Basin have been the subject of those studies, there are still uncertainties as totheir division and distribution, due to lack of consensus about the stratigraphy.Figure 1- Location of study area.The present study aims to investigate the risk of salinity in groundwater from deep wells,contributing to a better understanding of the hydrochemical characteristics of the study area inorder to support the proper management of these aquifers.2. MATERIALS AND METHODSThe methodology consisted of a georeferenced record of deep wells, collection of water in16 wells (Figure 2) for physical and chemical analyses, hydrochemical classification throughthe total dissolved solids (TDS) - salinity and salinity risk classification using the USSLsoftware of the United States Salinity Laboratory.153

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives3. RESULTSFigure 2- Location of wells.Groundwater salinity ranged from freshwater (10 samples) to brackish (6 samples) withvalues of 159.9 mg/L to 1038.7 mg/L. The distribution of brackish water occurs in differentaquifers in the region (Fluvio-deltaic, Sao Tomé I, Sao Tomé II and Barreiras) except in theaquifer Emborê. It can be observed that the well with the highest level of salinity - 1038mg/L - occurs in the São Tomé aquifer and has a depth of 170 m, while the well withlower salinity is located in the Fluvio-deltaic aquifer, at a depth of 70 m. B oth a r e farfrom the coastline. The Emborê aquifer occurs along the coastline but is the one with thehighest quality water up to a depth of 220 m. This is probably due to a water circulationpattern with recharge coming from the freshwater lagoon system located distant from the coastthat provides the confined aquifer a hydraulic head high enough to maintain a large freshgroundwater reserve near shore and even offshore – see Figure 3 (Capucci, 2006).The risk of salinity in groundwater ranged from high (6 samples), medium (9 samples) tolow (1 sample).The waters were in general classified as brackish, with a high risk of salinity,corresponding to the aforementioned aquifers. The Emborê a q u i f e r is the exception withfreshwater that poses a medium risk of salinity. According to the results of this survey, weconclude that the use of groundwater from deep wells in terrestrial Campos basin areamust be preceded by detailed studies and aquifer monitoring, to ensure a proper154

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesmanagement of these resources, so important to the Northern Region of Rio de Janeiro State.Figure 3- Emborê aquifer groundwater circulation model (Capucci, 2006).4. REFERENCESCAETANO, L. C. 2000. Água Subterrânea em Campos dos Goytacazes – RJ: uma opção parao abastecimento. Dissertação. Programa de Pós-Graduação em Administração e Política emRecursos Minerais. Universidade Estadual de Campinas, Instituto de Geociências - Campinas,SP. 112p.CAPUCCI, E. B. 2003. Água Subterrânea na Baixada Campista. I Simpósio de Hidrogeologiado Sudeste. Petrópolis, RJ. Anais. ABAS.CAPUCCI, E. B. 2006. A importância social, econômica e ambiental das águassubterrâneas para abastecimento aos Distritos da Baixada Campista e São Joanense.Nota Explicativa.CPRM/RJ 2001. Projeto Rio de Janeiro. Companhia de Pesquisa de Recursos Minerais.Ministério das Minas e Energia. Secretaria de Minas e Metalurgia / Companhia de Pesquisade Recursos Minerais. CD-ROM. Brasília.MARTINS, A. M.; CAPUCCI, E.; CAETANO, L. C.; CARDOSO, G.; BARRETO, A. B. C.;MONSORES, A. L. M.; LEAL, A. S.; VIANA, P. 2006. Hidrogeologia do Estado do Rio deJaneiro – Síntese e estágio atual do conhecimento. In: XIV Congresso Brasileiro de ÁguasSubterrâneas, Curitiba. Anais. Paraná. Associação Brasileira de Águas Subterrâneas, 2006.p.1-17.155

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSALTWATER INTRUSION IN COASTAL AQUIFERS AND INTEGRATEDWATER RESOURCES MANAGEMENTGiovanni BARROCUHbarrocu@unica.itHUniversity of Cagliari, ItalyCoastal areas, intended as the transition zones between continents and seas, are catchment final partswhere the natural fragile interface equilibrium between fresh, brackish and salt water may be easilyaffected by groundwater drawdown due to overexploitation and mismanagement, artificial run off due toirrigation and drainage, land and water uses, and urban infrastructure constructions, so that the naturalwater cycle is endangered. This equilibrium is, of course, strongly dependent upon sea level variations dueto subsidence and/or changing climate.Coastal aquifers are important sources of freshwater at risk, especially in deltas, where population densityin urban areas and straggling settlements is often highest and pollution due to agriculture and industry maybe very strong. As far as possible, fresh ground waters are to be considered strategic resources especiallyfor drinking purpose whereas surface waters, treated used waters, and desalinized waters may be allocatedto meet other users’ demand.Groundwater in coastal areas generally consists of fresh water floating on saltwater in variableproportions, but fresh water quality may be strongly endangered by saltwater intrusion and it is more andmore degraded owing to an increasing demand for domestic, agricultural and industrial supply as a largeproportion of the world’s population (about 70%) dwells in coastal zones. Furthermore, saltwaterencroachment and pollution progressively jeopardize the ecosystem of the emerged and submerged coast,and available water resources become scanty. Appropriate water resources management and preventiveand remedial actions are needed to settle arising conflicts among different users. The conceptual model ofsaltwater intrusion in coastal areas is rather more complex than the model envisaged by Ghijben, in 1988-89 and Herzberg, in 1901 with a sharp interface under hydrostatic conditions, at the local depth of around40 times the hydrostatic head, depending on seawater density. The thickness of the diffusion zone varieswith the hydrodynamic level.On the one hand, surface waters drainage and drawdowns produce gradient inversions with lateral inflowand upconing of present and connate waters of different salinity; on the other hand, polluted watersdrained in canals from inland areas may infiltrate directly into the terrain or outflow into coastal pondwaters interconnected with the sea and aquifers. Thus, saltwater encroachment may be due not only toimbalance between aquifer recharge and withdrawal.Lateral sea water may be entrained if the drawdown is deep and/or its influence radius intersects theshoreline, irrespective of the available amount of aquifer fresh water recharge.156

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGroundwater withdrawals to meet water demand can reduce wetland levels, which otherwise can beincreased by groundwater return flows from irrigation, and sewage discharge. Coastal aquifer degradationdirectly affects coastal wetlands and their ecosystems.Groundwater chemical status is strongly influenced by seawater intrusion. Some parameters so farregarded as invariable, such as actual porosity and hydraulic conductivity, may change with increasingsalinity, resulting in pH variations, element desorption from clay and groundwater, and soilrecontamination due to pollutant mobilization. Mixing processes cause both salinity increase and otherchemical-physical parameters variation. Coastal aquifers affected by saltwater encroachment areparticularly vulnerable to “retoxification processes”, which may be observed where both, accumulation ofheavy metals in sediments and changes of the environmental conditions take place.Alluvial sediments serve as long-term skins for large stores of heavy metals, and through reverse chemicalprocesses, such as desorption and dissolution, they can revert into large sources of heavy metals inbioavailable form. Salinity increase, pH and Eh are the main activating factors of these processes becauseof their influence on cation exchange equilibrium.Furthermore, in the coastal aquifers of the Mediterranean, owing to excessive fertilizer application anduntreated wastewater discharge in agricultural areas, pollution is a serious problem that may makegroundwater unsuitable for drinking purposes.Coastal aquifers vulnerability to saltwater intrusion and pollution is strictly dependent on soil and bedrockpermeability and pollution sources types, and it is particularly high in fractured and karstic rocks.Integrated vulnerability zoning should be periodically validated by accurate monitoring before using it forassessing scenarios for planning coastal area management. In fact, monitoring carried out with direct andindirect methods is essential for determining and predicting groundwater deterioration, and assessing othermanagement activities in coastal aquifers. It implies the planning of the most effective field surveying, andgeo-referenced data processing, so as to zone protection areas with different degrees of integratedvulnerability and risk.Scientific and technical analysis based on hydrogeological investigations may put in evidence that coastalgroundwater pollution sources are not located in the coastal areas as defined by geomorphological andadministrative criteria but are to be looked for even far upstream of costal zones. Such cases are foreseenin the Article 8 of the Barcelona “Convention for the Protection of the Marine Environment and theCoastal Region of the Mediterranean and its Protocols”, saying that the Contracting Parties shallendeavor to ensure that their national legal instruments include criteria identifying and delimiting,outside protected areas, open areas in which urban development and other activities are restricted or,where necessary, prohibited for the sustainable use of the coastal zone.On the one hand, there is the problem of outlining, as far as possible in detail, the hydrogeological,conceptual and numerical models of the catchment, considering surface and groundwater hydrology, land157

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivescover and uses, land and water resources vulnerability, interactions between surface waters andgroundwater of different quality with particular regard to coastal areas; on the other hand, water resourcesavailable should be assessed against water demand and infrastructure and running costs.Oceans and particularly almost closed basins like the Mediterranean and Black Sea receive greatquantities of organic and inorganic pollutants transported by inflowing coastal surface and ground waters.In coastal areas tourism represents an activity of increasing economic relevance, requiring the allocationof great quantities of fresh water not easily available to the detriment of other economic sectors andconsequently of the people living in the vicinity and the environment. Of course, economic and marketconsiderations should not be put before social considerations.Saltwater intrusion as a result of groundwater overexploitation is a major concern in many aquifers. TheUNESCO-IHP Sub-component 1.1 on “Managing Coastal Aquifer and Groundwater” of the GEFUNEP/MAP “Strategic Partnership for the Mediterranean Sea Large Marine Ecosystem(MedPartnership)” foresees the organization of a shared data bases of representative Mediterraneancoastal aquifer systems mainly concerning hydrogeological characteristics, management problems,priorities, and technical, administrative, law and financial aspects.A common effort is to be made to converge towards common management criteria of sustainableresources development, so as to prevent conflicts among different users. International cooperation isneeded for transboundary coastal aquifer management. Hopefully, best agricultural practices should becommonly adopted and wastewaters should be treated as respectively recommended by EC Directives No.271/1991 and 796/2004. Sustainable water resource management in coastal areas requires an integratedvision based of all aspects to be taken into account: climatic conditions and hydrology processes,hydrogeological characteristics, water allocation schemes combining both, efficiency and equityprinciples, water supply infrastructures, and needed engineering works. Primary criteria to alleviatepressure on water resources overexploitation are an effective water demand management and water useefficiency. Users should be informed and educated to reduce the use of fertilizers and pesticides, andincentives should be given to reduce and displace industrial and agriculture activities from vulnerableareas so as to mitigate their impacts in coastal areas (Fig. 1).Hydrogeologists are entitled to give stakeholders, regional planners and administrators all scientific andtechnical concerning details on the actual availability of groundwater in terms of quantity and quality to besurveyed in monitoring systems, so as to meet all users’ present and future demand. They can suggest thecorrect criteria and methods to be adopted for the best integrated sustainable exploitation and managementof all.Groundwater should be assessed and managed in terms of integrated water resources to meet waterquantity and quality demand for different uses, considering the conventional and unconventional waterbalance of the hydrogeological catchments, different areas of interest, and supply costs.158

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 1 – Human activities impacts on coastal areasCoastal aquifer vulnerability zoning should be periodically validated by accurate monitoring before usingit to assess integrated vulnerability scenarios in planning coastal area management. Monitoring carried outwith direct and indirect methods is essential to determine and predict groundwater deterioration, andassess other management activities in coastal aquifers. It implies the planning of the most effective fieldsurveying, and geo-referenced data processing, so as to zone areas with different degrees of integratedvulnerability and risk. As most aquifers of different types are heterogeneous and anisotropic, a suitablemonitoring scale should be chosen to represent their characteristics in all details needed by decisionmakers.The management of coastal waters and areas requires interdisciplinary collaboration among differentexperts on water resources and land planning, agronomy, biodiversity, economy, water laws anddirectives. Promoting joint management of shared aquifers is a need. Hydrogeologists’ contribution isessential in developing Integrated Water Resources Management (IWRM) policies, concerningtechnology, strategic and project planning, economic instruments, regulations, efficiency of GWadministration, and decision making.Science may give the right answers to plan the best actions necessary to manage land and water resourcesin a sustainable way so as to prevent conflicts among different users and in the respect of theMediterranean environment.159

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTEMPERATURE AS TRACER FOR SURFACE WATER – GROUNDWATERINTERACTIONS IN THE RAVENNA COASTAL PLAIN, ITALY.VANDENBOHEDE, A.; ANTONELLINI M.; GREGGIO, N.; MOLLEMA, P.;PANDOLFINI, M.alexander.vandenbohede@ugent.beGhent University; University of BolognaKrijgslaan 281(S8), 9000 GentAbstract. An important application of temperature measurements in the field of hydrogeologyis the characterization of natural or artificial recharge and the interaction between surfacewater bodies and ground water. Recharge can influence the shallow temperature variationsin an aquifer forming a potential tracer for characterizing this recharge. Temperature of thepore water varies seasonally. Variation decreases deeper in the aquifer defining a zone ofinfluence: the surficial zone. Temperature profiles (temperature versus depth) and the depthof the surficial zone are influenced by temperature variations of recharge water, rechargevelocity, sediment properties and groundwater flow. Increased recharge (e.g. due toirrigation) increases the depth of the surficial zone whereas upward flow (e.g. to a drainageditch) results in a decrease. Temperature profiles can thus be used as a tracer in groundwaterflow systems. This is applied here in the coastal area of Ravenna, Italy. The study area is partof the Po River Plain, bordering the Adriatic coastline. It is characterized by river and canalmouths, wetlands, an old and a young dune system, lagoons, heavily developed areas,industrial facilities, harbors and reclaimed agricultural land. It is a Mediterranean studyarea with relatively cold humid winters and warm dry summers resulting in a period of verylittle natural recharge. Main impoldering activities occurred between 1950 and 1980 and thisresults in a current complex distribution between fresh and saltwater. Temperature profilesare available in about 50 wells distributed in young and old dunes, in the polder, and near acoastal lagoon. SEAWAT v4 is applied to simulate temperature profiles using a typicalgeological cross-section, recharge estimates and annual temperature variations in the studyarea. These profiles are compared to observed temperature profiles. The results show adistinction between areas where there is natural recharge, influence of irrigation ditches andinfluence of the lagoon and quarries. During the dry summers without natural recharge,irrigation is applied causing artificial recharge. This artificial recharge is an importantfactor for freshening of the aquifer and temperature profiles provide a way to estimate thisfreshwater recharge. Combination of simulation of the heat transport and the fresh-saltwaterdistribution can further validate this estimation.Keywords: temperature; tracer; combination with salinity160

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTHE WATER FARMVan BAAREN, E.S.; OTTOW, B. T.; PAUW, P. S.; Van EK, R.; De LOUW, P. G. B.esther.vanbaaren@deltares.nlDELTARESAbstract. The Water Farm is a cooperation of farmers, landowners, municipality, waterboard and residents to manage (receive, store, use, process, deliver) fresh water in the regionsuch that no water from elsewhere needs to be invoked. InnovatieNetwerk, TransForum andAequator developed the concept. Rijkswaterstaat and Deltares joined to start a pilot: if aWater Farm can be realized, large investments in the water supply can be prevented. Thewaterboard and ZLTO advised Walcheren; an area already independent in the fresh watersupply and hence a good location to start a pilot. Fresh water is available: precipitationsurplus, fresh seepage from dunes and some fresh groundwater. However, the farmersexperience 10-30% drought damage. Groundwater is mainly saline so groundwater wells arelimited, ditches are saline due to saline seepage and the precipitation surplus is discharged tothe sea. Climate change predicts an increase of dry periods and models predict salinisation ofthe groundwater. This sense of urgency is felt by the 10 farmers now working together toconcrete their Water Farm.; During the project the main goal was to establish the feasibilityand conditions of the formation of the Water Farm. We determined the (geo)hydrologicalfeasibility by combining our scientific with the farmers practical knowledge. The economicalfeasibility was determined for each individual entrepreneur. Discussions were held with thewaterboard, municipality, county estate owners and nature organizations. Results arepromising for farmers and nature; enough fresh water available, storage possible (in thesubsoil, in the groundwater or in basins) and by working together, this can be realized. Now,the farmers continued the Water Farm Walcheren independently and started with therealization of their plans. Making a new Water Farm a success starts with the presence offresh water and a sense of urgency by the entrepreneurs. One key ingredient for the process isbuilding up faith by ambassadors from the region, common interests and participation incollecting new knowledge. Other important ingredients: cooperating Waterboard, broadspectrum of measures (individually as well common) and starting new hydrological researchto answer practical questions. This last key ingredient has a follow up within ‘Knowledge forClimate’: in 2012 a field experiment starts to increase the fresh water lens in the groundwaterin a sandy creek in winter for irrigation in summer.Keywords: innovation, fresh water supply, farmers, pilot, salinisation161

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesUSING DENSITY DIFFERENCE TO STORE FRESH WATER IN SALINE AQUIFERSM. van Ginkel 1,2 ; T.N. Olsthoorn 1,3 ; B. des Tombe 1m.vanginkel@tudelft.nl1 - Delft University of Technology; 2 - Royal Haskoning; 3 - WaternetPO Box 8520; 3009 AM Rotterdam; the NetherlandsAbstract. Two concepts for the storage of fresh water in saline aquifers are presented. Freshwater storage in saline aquifers poses a challenge: the initially vertical interface betweeninjected fresh and native salt water is unstable and tends to rotate. The injected fresh water tendsto float upward on top of native salt water, where it becomes hard or impossible to recover at alater stage. A wide body of literature exists about this buoyancy effect that is caused by thedensity difference between fresh and salt water. Yet, very few articles focus on solutions to thisproblem. In this study we propose two concepts for the storage of fresh water in saline aquifersto overcome this buoyancy problem by actually using the density difference to keep the freshwater in place, by combining fresh water storage with salt water extraction (“FSSE-well”) orimpermeable barriers (“Storage Tank”). These systems seem promising and might solve manylocal fresh water storage problems.Keywords: Aquifer Storage Recovery, saline aquifers, density differenceINTRODUCTIONThis paper considers Aquifer Storage Recovery (ASR) in brackish or saline aquifers. ASR insaline aquifers appears technically feasible. Injected fresh water displaces the native salt water inthe aquifer during injection. On the fringes mixing will take place, and a mixing zone betweenthe two water types is present, separating the injected fresh water from the native salt water inthe aquifer. The development of the mixing zone may be considered an investment in ‘salinitywalls’ (Pyne, 2007) as it, once build, kind of prevents losses in future cycles of operation.However, due to the density difference between fresh and salt water, the initially verticalinterface between the two water types is unstable and is going to rotate (Bakker, 2010). Thelighter fresh water tends to float up to the top of the aquifer and spread out, where it becomeshard or impossible to recover at a later stage. This problem may be less evident in well-knownsystems with continuous recharge of fresh rainwater, causing a permanent fresh water lens tofloat on saline water in a permanent dynamic fashion. However, a dynamic equilibrium cannotbe maintained in situations that only relatively small amounts of fresh water are stored and thereis no continuous recharge; in that cases buoyancy of fresh water is going to occur.162

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesThis buoyancy effect highly reduces the recovery efficiency, which is defined as the ratiobetween injected and recovered fresh water of ASR-systems in saline environment. A wide bodyof literature studies this buoyancy effect. A review of density effects in ASR-systems is given inWard et al (2007).This study aims to find appropriate ways to store fresh water in saline aquifers by actually usingthe density difference between fresh and salt water, in combination with civil engineeringtechniques and the characteristics of the aquifer.INCLINATION OF THE INTERFACEThe inclination of the interface (Bear, 1978) is expressed byρfqf− qssinα = ρ − ρ KsfWhere α [] is the inclination angle of the interface, ρ [M/L 3 ] and ρs fs[M/L 3 ] are the densities ofthe fresh and salt water respectively, K [L/T] is the hydraulic conductivity of the aquifer, qf[L/T]and q [L/T] are the groundwater discharges on either side of the interface and directed along it.sThis formula assumes a steady-state, hence equilibrium interface position.This formula implies that the inclination of the interface is maintained as long as there is agroundwater velocity difference between the stored fresh and present salt water. The interface isgoing to be horizontal when the velocity difference equals zero, i.e. when no injection of freshwater or flow of salt water occurs. Based on this analysis we developed two concepts to storefresh water in saline aquifers: the “FSSE-well” and the “Storage Tank”.FSSE-WELLThe main characteristic of the Fresh Storage Saline Extraction (FSSE)-well is that continuouspumping of salt water at a limited rate from below the stored cone-shaped fresh water lensmaintains the interface inclination and effectively “glues” the stored fresh water to the well. Theprinciple of saltwater extraction is visualized in figure 1, showing a FSSE-well with its twoscreens. The upper screen injects and extracts fresh water, but in this figure, the fresh water is inits stagnant storage phase, while salt water is extracted with the lower screen. An analyticalsolution for the storage phase and a numerical analysis of the dynamic behaviour of the freshwater lens is given in Van Ginkel et al (2010). The stored and recoverable volume depends onmany factors including porosity, thickness, hydraulic conductivity, heterogeneity, salinity andambient flow and operations.163

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFigure 1 Cross section of a Fresh Storage Saline Extraction (FSSE)-well during the storage phaseSuch wells are particularly useful in situations where water supply is dependent on groundwaterdesalination and large fluctuations in demand occur. Hence, the FSSE-well is generallyapplicable for seasonal storage of desalinated drinking water at desalination plants of resorts inarid countries or islands. In these situations, continuous low-rate pumping of salt water presentsno loss, as a rate of fresh water production is required even in low-demand periods.STORAGE TANKIn situations where continuous salt water extraction is not attractive and continuous fresh waterrecharge is not possible, fresh water can be stored in saline aquifers by means of the StorageTank. The Storage Tank uses vertical barriers partially embedded in a saline aquifer to preventfresh water from spreading out and drifting away. The principle is visualized in figure 2. Theimpermeable barriers are constructed of sheet piles, clay or other types of impermeable material.The salt water below is functioning as the Storage Tank’s variable bottom. Des Tombe et al(2012) did a numerical analysis to investigate the influence of the width, depth and aquifercharacteristics on the recovery efficiency, and laboratory experiments to verify the numericalmodel.Figure 2 Cross section of a Storage Tank during the storage phase164

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesStorage by means of the Storage Tank may be beneficial in shallow saline water-table aquifersfor the storage of collected rainwater or treated waste water. Application is possible at differentscales. At household plot the Storage Tank may be used for the small-scale storage of rainwateror treated waste water for irrigation or household purposes. Large-scale opportunities are thestorage of irrigation water (usually treated waste water) in shallow water-table aquifers belowparks or arable land, such that roots can reach fresh groundwater. In this way, the Storage Tankmay be an alternative for intensive drip irrigation systems.FURTHER RESEARCHSo far, the FSSE-well and the Storage Tank have been analyzed from the point of view ofgroundwater hydraulics to examine their geohydrologic feasibility and to learn about theoperations and design criteria necessary to make such systems a success in practice.Until now, the study mainly focused on the storage phase, with little attention to the injection andrecovery phase. Further research will include a modeling study to investigate optimal injectionand recovery techniques including the effects of evaporation.Field experiments should be carried out before these systems can be used on large scale. Theresults of a pilot project will give insight in well design, well construction and operation,recovery, mixing characteristics, water quality changes and the effect of storage time on waterquality and recovery efficiency.REFERENCESBakker, M., 2010. Radial Dupuit interface flow to assess the aquifer storage and recoverypotential of saltwater aquifers. Hydrogeology Journal vol 18, p 107-115.Bear, J., 1978. Hydraulics of groundwater. Keterpress Enterprises, Jeruzalem, Israel.Des Tombe, B., Van Ginkel, M., Olsthoorn, T.N., 2012. Aquifer Storage Recovery, The StorageTank Method. Can the Storage Tank method increase the recovery efficiency?Pyne, R.D.G., 2007. Aquifer Storage Recovery: a guide to groundwater recharge through wells.ASR systems LLC, Gainesville, Florida, USA.Van Ginkel, M., Olsthoorn, T.N., Smidt, E., Darwish, R., Rashwan, S., 2010. Fresh StorageSaline Extraction (FSSE) wells, feasibility of fresh water storage in saline aquifer with a focus onthe Red Sea coast, Egypt. ISMAR7 proceedings.Ward, J.D., Simmons, C.T., Dillon, P.J., 2007. A theoretical analysis of mixed convection inaquifer storage and recovery: How important are density effects? Journal of Hydrology, vol 343,p 169-186.165

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTHE ROLE OF RECHARGE AND MIXING PROCESSES TO EXPLAINFRESH WATER LENS DYNAMICS BELOW A SMALL ISLANDCONDESSO DE MELO, M.T. 1 ; POST, V.E.A. 2 ; WATERLOO, M.J. 3 ;GROEN, M.M.A. 3vincent.post@flinders.edu.au1. Flinders University, School of the Environment2. National Centre for Groundwater Research and Training, Adelaide, AustraliaGPO Box 2100, Adelaide, SA 5001, Australia3. VU University, Faculty of Earth and Life Sciences, Amsterdam, The Netherlands;Abstract. During the 21st Salt Water Intrusion Meeting, Post et al. (2010) presented aconceptual model for the distribution of fresh and saline groundwater below a small sandyisland in the Ria de Aveiro Lagoon in Portugal. The conceptualization was based on fielddata, but relied heavily on numerical modeling as well. The numerical model indicated thatthere is outflow of relatively fresh groundwater near the low water line of the sloping beach,but, at the time, this could not be confirmed in the absence of field data. Here we present newdata that validate the model outcomes in a qualitative sense, and show that the outflowspredicted by the model indeed occur. The results indicate that the presence of a salinecirculation cell below a sloping beach, as well as a ‘tube’ of seaward-flowing, relatively freshgroundwater underneath, is likely to be a general feature of shallow coastal groundwatersystems, even where the recharge area is small. We also provide new data on the transientbehavior of the vertical salinity distribution as observed in multi-level observation wellsduring the summer and winter season, as well as measurements with a high temporal andspatial resolution of the movement of the transition zone during a tidal cycle. Thesemeasurements provide insight into the role of recharge and mixing processes in explainingthe observed shape and position of the transition zone between fresh and saline groundwater.Based on a comparison of these observations with numerical model outcomes, theappropriateness of current process descriptions of mixing in models is discussed.REFERENCES Post, V.E.A., M.J. Waterloo, M.M.A. Groen and M.T Condesso de Melo(2010) Field data and numerical simulation of a fresh water lens below a small island with astrong tidal regime. Procedings of the 21 Salt Water Intrusion Meeting, Azores, Portugal.Keywords: tides; islands; mixing166

New approaches onmodelling (general methodsand solution of real cases)

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA HYBRID FEFV REACTIVE SEAWATER INTRUSION MODELNICK, H. M. 1,3 ; CENTLER, F. 2 ; REGNIER, P. 3 ; THULLNER, M. 1,2h.m.nick@uu.nl1. Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands;2. Department of Environmental Microbiology, UFZ – Helmholtz Centre forEnvironmental Research, Leipzig, Germany;3. Department of Earth and Environmental Sciences, Université LibreP.O. Box 80.021 - 3508 TA UtrechtAbstract. Reactive flow and transport in coastal aquifers is difficult to predict as it dependson the mixing of seawater/groundwater and the local balance of viscous and gravitationalforces as well as on reaction kinetics. The reactive mixing between seawater and terrestrialwater in coastal aquifers influences the water quality of submarine groundwater discharge(SGD). While these waters come into contact at the seawater-groundwater interface due toadvective, density driven flow, their chemical components dilute and react controlled bydispersion. For example, removal processes such as biodegradation of dissolved organiccarbon can occur at the mixing between seawater and terrestrial water, affecting the SGD.Hydro-biochemical processes are influenced by various factors and their dynamics can varyconsiderably in coastal aquifers. Understanding the mechanisms controlling such processesis essential to determine the subsurface pathways and fluxes of land-derived chemicals to themarine environment. Here we present a hybrid finite-element finite-volume method (FEFVM),which is developed using CSMP++, and combined with a Biogeochemical Reaction NetworkSimulator (BRNS). This framework gives major advantages over many previously developedmodels, as it benefits from using: A non oscillatory second-order implicit scheme for timedependentadvection-dispersion equations suitable for heterogeneous media; A hybridFEFVM capable of capturing discontinuities at the material interfaces; and, a comprehensivereaction algorithm simulating microbiological and geochemical processes. To study the effectof hydrodynamic dispersion, gravity driven flow and reactivities of chemical components onthe chemistry of SGD the fate of a hypothetical contaminant plume approaching the coast lineis simulated. A simple redox reaction is considered to describe the degradation of thecontaminant and mixing between the contaminated groundwater and the sea water containingthe terminal electron acceptor is required to facilitate the reaction. The resulting degradationis observed for different scenarios considering different magnitudes of dispersion andchemical reactivity. Results indicate that both, the kinetics of the degradation as well astransversal dispersion determine the extent of mass removal in coastal aquifers. Further, ourresults confirm that the dilution index is a better alternative to the second central spatialmoment of a plume to describe the total degradation.Keywords: Reactive transport; density driven flow, FEFVM169

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesBEACH GROUNDWATER OVERHEIGHT IN REGIONAL GROUNDWATERFLOW STUDIESPAUW, P. S.; Van Der ZEE, S.E.A.T.M.; OUDE ESSINK, G.H.P.pieterpauw85@gmail.comDELTARES; WAGENINGEN UNIVERSITYAbstract. Large parts of the coast of the Western Netherlands are subjected to structuralmarine and eolian erosion. In order to safeguard a robust coastal defense, the shoreline isartificially preserved using beach and nearshore sediment nourishments. This practice islikely to increase in the future in order to cope with the relative sea level rise that has beenprojected for the Netherlands. Moreover, additional nourishments can be expected fromfuture plans of artificial coastline progradation, which have been defined in 2008. Shorelineprogradation results in an expansion of the coastal dune area, which renders great addedvalues to society such as increased space for recreation, water supply and naturedevelopment. In 2011, a field pilot study of a mega-nourishment of approximately 20 Mmstarted near the city of The Hague. Shore-parallel transport of this sediment will result in agradual progradation of the shoreline for the next 10 years. Artificial coastline progradationin the Netherlands influences the regional dune groundwater flow system. The quantificationof the hydrological impacts necessitates an accurate representation of the seaward boundary.Regional numerical groundwater studies have generally neglect beach groundwater flow andassumed a static seaward boundary condition. Amongst others, an oscillating sea level andthe presence of sloping beach results in hydraulic heads at the beach that are on averagehigher then the mean sealevel. This phenomenon is known as beach groundwater overheight.Beach groundwater overheight is controlled by the tidal range, hydraulic conductivity of thebeach sediments and the beach slope. Neglecting this process in regional coastalgroundwater flow studies seems reasonable if the scale of the problem is large or when theoverheight is insignificant, but is questionable when the groundwater flow system reachessmaller scales and the overheight is large. The objective of this study is to determine underwhich circumstances beach groundwater flow should be taken into account regional coastalgroundwater flow studies. The numerical density dependent flow and solute transport codeSEAWAT is used to construct models simulating regional coastal groundwater flow. Thesemodels are used to determine under which circumstances beach groundwater flow should beincorporated. Preliminary results of these models will be presented.Keywords: beach groundwater table overheight; coastal dunes170

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCALIBRATION OF A DENSITY DEPENDENT MODEL OF A SYSTEM FORAQUIFER THERMAL ENERGY STORAGE, BASED ON THE MEASUREDDATA OF A HEAT INJECTION SYSTEMSMITS, F.J.C.; OLSTHOORN. T. N.; CALJÉ, R. J.frank.smits@waternet.nlWATERNET & TECHNICAL UNIVERSITY OF DELFTAbstract. Aquifer Thermal Energy Storage (ATES) systems store cold and warm water inorder to use it for climate control of buildings at a later time. Groundwater is pumped up tocool a building during summer and the warmed-up water is injected into another well, to forma warm bubble in the aquifer. The flow is reversed during the winter season, and water fromthe warm bubble is used to heat the building. The cooled water is injected in the other well toform a cold bubble for next summer. ATES is being used more frequently in the Netherlandsin the last years, caused by the increased demand for sustainable energy and the rising costsfor conventional energy. Large buildings have their own system, but for smaller buildings thisis not profitable. To let smaller buildings also profit from ATES, Waternet works in thehistoric centre of Amsterdam on a project to install a collective system, with at least sixconnected buildings. A heat injection system was operated at this location from 1989 to 1999to cool a data center. Two wells extracted cold water from the upper part of the aquifer andthe warmed-up water was injected with three wells in the lower part of the aquifer. Thegroundwater was only pumped in one direction, which caused the aquifer to be subject ofthermal pollution. The warm plume reached the cold wells after a couple of months ofpumping. The cold wells were warmed-up too much after four years, so it was decided to drillanother cold well, farther away from the injection wells. In 1999 this new well also warmeduptoo much, and the system was abandoned. This system was modeled with SEAWAT, withthe discharges and the temperatures of the injection wells as boundary conditions. Themeasured temperatures of the abstraction wells were used to calibrate the model with PEST.Model results depended on both temperature differences and the differences in saltconcentration between the upper and lower parts of the aquifer. The presentation will show: -measurements of a system of heat injection, - that differences in density caused by differencesin both temperature and salt concentration can be important when modeling thermal systems,- that a system for heat injection can spoil the aquifer for a long period, - that it is importantto balance the injected amount of heat and cold in the aquifer to keep ATES systemssustainable, - that PEST helped with optimizing the model, - that the model improvedunderstanding of the important processes.Keywords: groundwater; heat injection system; thermal pollution; Aquifer Thermal EnergyStorage (ATES); sustainable energy; differences in temperature; differences in saltconcentration; differences in density; SEAWAT; MFLAB; PEST171

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCOUPLED HYDROGEOPHYSICAL INVERSION FOR A SALT WATERINTRUSION MODEL AND TIME-DOMAIN ELECTROMAGNETIC (TDEM)DATAHERCKENRATH, Daan; DUQUE-CALVACHE, C.; NENNA, V.; ODLUM, N. J.;KNIGHT, R.; BAUER-GOTTWEIN, P.daah@env.dtu.dkTECHNICAL UNIVERSITY OF DENMARKMiljovej; building 113; Kgs. Lyngby; 2800; DenmarkAbstract. Coupled hydrogeophysical inversion approaches (CHI) have been increasinglyused to extract hydrological information from geophysical datasets. In a CHI hydrogeologicalparameters are estimated by translating hydrologic model simulations into geophysicalimages using petrophysical relationships. This is done by varying hydrological modelparameters until the observed geophysical data is fit. CHI has a potential for improving themapping and simulation of saltwater intrusion since large-scale Time-DomainElectromagnetic (TDEM) datasets have become available. These datasets can provide threedimensionalelectrical resistivity models of the subsurface, which can be correlated with thedistribution of saltwater and freshwater within coastal aquifers. For our scoping study, weperform a CHI for a field site in California. We estimate five uniform aquifer properties for across-sectional salt water intrusion model using observed TDEM data. In addition to thehydrologic parameters, we estimate one petrophysical and one geophysical parameter. Theseseven parameters could be well resolved by fitting more than 300 apparent resistivities thatcomprise the TDEM dataset. Except for 4 soundings the TDEM data could be fit close to anRMSE of 1. The poor data fit of these 4 soundings is likely due to the assumption of spatialuniformity and 3D effects in the TDEM forward responses. The electrical resistivity modelsthat resulted from the CHI provided a large improvement in spatial resolution, which wouldbe difficult to obtain with traditional geophysical inversion approaches as the complex spatialcorrelation between geophysical parameters cannot be captured with standard regularizationconstraints. To summarize, our study emphasizes the potential of CHI to improve thesimulations of salt water intrusion models. In combination with such models, this couldprovide an opportunity to use TDEM data as a non-invasive real-time monitoring tool tosupport groundwater management.Keywords: geophysics;modeling;parameter estimation; coupled inversion172

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesDENSITY FLOW MODELING WITH MFLAB, EXAMPLESOLSTHOORN, T. N.; NIENHUIS, P. N.t.n.olsthoorn@tudelft.nlTU DELFT, CITG, ROOM 4.96Stevinweg 1, 2628 CN Delft, Room 4.73Abstract. Density flow modeling with mfLab, examples Theo N. Olsthoorna,b, Philip N.Nienhuisa a Waternet, Vogelenzangseweg 21, 2114 BA Vogelenzang, the Netherlands b DelftUniversity of Technology, Department of Civil Engineering, Stevinweg 1, 2826 CN Delft, theNetherlands mfLab is a free modeling environment available at www.code.google.com. It usesMatlab to specify models and to subsequently generate input files of MODFLOW, MT3DMS,SEAWAT and SWI codes. It focuses on reproducibility and flexibility by scripting modelspecification in Matlab and using Excel as a multipage documented repository of theparameters required by the mentioned model codes. The combination is extremely flexibleand adaptable for adding features and combining with databases or codes such as PEST,while the entire computation and visualization capabilities can be used and combined. As aspecial feature, mfLab is extremely good in handling axial symmetric flow problems: anymodel is turned made axial symmetric with by setting a single variable. When invoked mfLabreads the specified model arrays, reads the parameters for the models from the Excelworkbook, generates the input files of the underlying models and launches the necessarymodel codes. When the latter have finished, mfLab reads their output and processes,visualizes and animates their results. Many animations have been placed on YouTube asexamples for modeling density flow and freshwater storage problems, with and withouttemperature effects (look for mfLab and groundwater). Advantages of mflab are full freedomin specifying model and extreme flexibility in changing grids at any time, definingvisualizations, extending models, building on previous ones and reproducibility by exploitingthe capabilities of Matlab and Excel. It has been shown to work one to one also with Octaveinstead of Matlab, making the environment free of cost for those who do not have access toMatlab. The working of mflab with different examples will be shown.Keywords: Density modeling; user interface; modeling environment173

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesIDENTIFICATION AND ESTIMATION OF GROUNDWATER INFLOW INTO ABRACKISH LAGOON: FIELD OBSERVATIONS AND MODELING OF SEASONALCHANGES IN DISCHARGEKinza Haider 1 ; Peter Engesgaard 1 , Torben Obel Sonnenborg 2 ; Sabrina Jensen, Carlos Duque 1kha@geo.ku.dk1 Department of Geography and Geology, University of Copenhagen, Denmark; 2 Departmentof Hydrology, Geological survey of Denmark and Greenland, DenmarkDepartment of Geography and Geology, Øster Voldgade 10, 1350 Copenhagen, DenmarkAbstract: Groundwater discharge into a brackish lagoon (Ringkøbing Fjord, Denmark) hasbeen studied using a combination of hydrogeological field investigations and variable-densityflow and transport modeling. A conceptual model of the dynamics controlling the interactionsbetween the more saline lagoon water and fresher groundwater is being developed on thebasis of different tracers with the objective of quantifying where, when, and how muchshallow groundwater discharges to the lagoon. Sampling of groundwater every two months inthe upper 2-3 m have been carried out and EC-depth profiles have been used to estimatechanges in the width of the groundwater discharge zone. Furthermore, temperature as atracer was used to estimate groundwater discharge indirectly. Field observations show thatthe salinity of the lagoon is highest in summer (~ 12 permil), when groundwater discharge islowest and, vice versa, lowest (~ 5 permil) when the discharge is highest (winter). Thisindicates that the forces of the saline intrusion and freshwater discharge are offset in timecreating a dynamic saltwater-freshwater interface (SWI)with maximum and minimum intrusions in the summer andwintertime, respectively. The Hydrogeosphere code wasapplied to simulate the transient conditions in the SWI. Thesimulations are based on the observed dynamic boundaryconditions of hydraulic head on landside and salinity/waterstage in the lagoon. The simulation results compare wellwith field observations: (1) the significant width of dischargezone lies around 20 m depending on the season with amaximum discharge near the shoreline, and (2) themaximum discharge is on the order of a few cm/daydecreasing rapidly off-shore with winter discharge being~15% of that during summer (~0.03 m/d).Key words: Lagoon, groundwater discharge, dynamic,saltwater-freshwater1. INTRODUCTIONFigure 1: Area of StudyThe main objective of this study is to locate, outline and estimate groundwater discharge(GWD) into a brackish lagoon, Ringkøbing Fjord in Western Denmark (Fig. 1). This will helpin closing the water balance of the Skjern river catchment by quantifying one outflowmechanism. The area of study is a bar-built estuary (~300 km 2 ) of controlled salinity (5-12permil) and water level (

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesincoming seawater. A combination of hydrogeological field investigation techniques wereused to understand the lagoon water-groundwater interaction which include; geophysicaltracers - temperature and electric conductivity, direct seepage meter measurements, andspatial distribution of electric conductivity in the lagoon water. Slugtests were carried out inthe sediment bed of the lagoon at depths up to 12 m to map the local hydrogeology of studyarea. The shallow aquifer system consists mainly of sand with clay lenses up to a depth of 3 m(~13m/d), proceeded by a 4 m thick layer of silty-sands (~5 m/d) and a 5 m thick layer ofclean sands (~22m/d). Below, a clay layer separates the deeper aquifer from the shallow one.2. CONCEPTUAL MODEL AND NUMERICAL MODELINGBased on the field observations onshore and offshore in the study area, a conceptual modelwas constructed (Fig. 2).Landsidehead&lagoonsalinitysinusoidalmodelsequenceZ=12m0masl450m3m7mHeaddhsmodelSsmodel0 50 100 150 200 250 300 350T(d)K13m/dK5m/dK22m/dSalinity0m50minland0.3masl50mWinterSummerSummerWinterx=500mFigure 2: Conceptual model showing geology and field conditions during winter and summerA Hydrogeosphere code (HGS) is used which solves the non-linear coupled densitydependentflow and transport equations. The model domain is a rectangular 2-D vertical crosssection (x–z plane) with 500 m x 12 m extent (Fig. 2). The lagoon boundary is locatedbetween 0-450 m (in x) at 0 m (in z), whereas the rest of the model domain is the main aquifersystem subdivided into three layers with thicknesses 3 m, 7 m and 12 m (Fig. 3) terminatingat impermeable lower boundary of the model (clay layer). The topography of the modelslopes slightly from 0 m to 0.3 m, between 0 – 50 m (in x) at the land side boundary. Thesimulated area is discretized in 261 columns and 75 rows with a graded mesh aroundshoreline (0 m in x) from 0.05 m to 2 m and in the upper 2 m (in z) from 0.05 m to 0.2 m. Theinitial freshwater-brackishwater distribution is based on summer time observations, where thesalinity in the lagoon is highest and the gradient at land side is lowest. In the transient model,two main variables are involved; the hydraulic head at the landside boundary and the salinitychanges in lagoon (in terms of relative concentration). Sinusoidal distributions for both thesevariables are specified in the model with a simulation run time of 10 years. Following the175

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivessinusoidal distribution of salinity in the lagoon, freshwater head in the lagoon water is alsospecified as a sinusoidal function, although the changes are subtle. The parameters arespecified in table 1.HydraulicConductivityModelbasedonfieldobservationsHK(m/d)0 5 10 15 20 25 30 350Table 1: Simulation parameters used for steady and transientmodelingDepth(m)24681012K=13m/dK=5m/dK=22m/dd=3md=7md=12mFigure 3: Hydraulic conductivity based on falling headmethod in shallow unconfined aquifer.Parameter Value UnitKx1, Kx2 & Kx3 13, 5 & 22 m.d -1Kz 0.1 Kx m.d -1Specific storage 1.0e-6 m -1Porosity 0.35 -Longitudinal dispersivity 0.1 mVertical transverse dispersivity 0.001 mTortuosity 1.0 -Maximum Fluid Density 1010 kg.m -3Reference Fluid Density 1000 kg.m -3Free-solution diffusion coefficient 0 m 2 .d -1Fluid compressibility 5.09e-15 ms 2 .kg -1Fluid Viscosity 97.1136 kg.m -1 .s -13. RESULTS AND DISCUSSIONThe temperature-depth (t-d) profiling data from May 2011, September 2011 and January 2012were used to estimate GWD into the lagoon (q z ). A steady-state analytical solution to the 1Dconduction-convection equation (Bredehoeft and Papadapulos, 1965) was fitted to theobserved t-d profiles by changing the Darcy flux (q z ). The simulated discharge by HGS(~0.01-0.11 m/d) compares well with observed discharge (~0.01-0.08 m/d) around theshoreline (Fig. 4). Furthermore, groundwater is only found to discharge at distances up to 20m out in the lagoon with an almost exponential decrease from the shoreline, also agreeingwith field observations. The observed maximum GWD in summer (September 2011) is about50% lower than that of winter maximum (January 2012) whereas this contrast is simulated as30 % between summer and winters. The electric conductivity-depth (EC-d) profiling was alsocarried out during different times of the year to observe changing patterns of salinitydistribution and widths of GWD zone from shoreline to around 20 m offshore. The EC datawas converted to relative concentration for comparison with modeling results of saltdistribution. The observed saltwater distributions in one of study transects in May 2011 andMarch 2012 show movement of the 50% saltwater line which indicates the dynamic nature ofthe interaction between groundwater and lagoon water (Fig. 5). The simulated saltwaterdistribution also shows movement of50% saltwater line between January,Groundwaterdischargeintothelagoon:SimulationvsObservations0.12SimJan SimMay SimSepMay, and September in line with fieldObsJan2012 ObsMay2011 ObsSep20110.1observations (Fig. 6). Furthermore,0.08both the simulated and observedsaltwater distributions show changes0.06in the widths of discharge zone0.04corresponding to 50% saltwater line0.02movement, maximum in winter and0minimum in summer in simulated 24 22 20 18 16 14 12 10 8 6 4 2 0results.Distancefromshoreline(m)Figure 4: Comparing simulated and observed GWD during January,May and September.4. CONCLUSIONS:The GWD into the lagoon is dynamic, dependent upon head on landside and salinityof thelagoon causing the width of discharge zone to move between 20-30 m with maximumqz(m/d)176

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesdischarge restricted to shoreline falling slightly exponential. With a 40,000 m lagoonshoreline of maximum GWD up to 20 m would yield 64,000 m 3 /d (simulated) and 88,800m 3 /d (observed) flux.Observed salt distribution (%) at transect C - May 2011 (top) vs March 2012 (bottom)0503010-0.5-1-1.5-2Depth under sediment bed (m)-19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0Distance from shoreline (m)070503010__ o Sampling point50% saltwater line-0.5-1-1.5-2-2.5-3Depth under sediment bed (m)-23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0Distance from shoreline (m)Figure 5: May 2011 and March 2012 observed saltwater distribution showing 50% contour line (Vertical Exaggeration 3x).Simulated saltwater distruibution (50% saltline) - January, May and September0__________Sim-Jan_____Sim-MaySim-Sep-0.5-1-1.5-2-2.5-3Depth under sediment bed (m)-23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0Distance from shoreline (m)Figure 6: January, May and September simulated saltwater distribution of 50% contour line (vertical exaggeration 3x).References: Bredehoeft, J. D. and Papadopulos, I. S., 1965. Rates of Vertical Groundwater Movement Estimated 520 from theEarth´s Thermal Profile. Water Resources Research 1, 325-328.177

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesINTERRELATION OF BRINE REFLUX AND MINERAL PRECIPITATION FRONTSIN AQUIFERS DURING NATURAL EVOLUTION OF SALT LAKESEnrico Hamann 1 ; Vincent Post 2 ; Claus Kohfahl 3 ; Henning Prommer 4ehamann@zedat.fu-berlin.de1 - Freie Universität Berlin (Germany); 2 -Flinders University Adelaide (Australia); 3 -Instituto Geológico y Minero de España, ( Sevilla, Spain); 4 -CSIRO Land and Water(Wembley, Western Australia, Australia)Enrico HamannFreie Universität BerlinHydrogeology groupMalteserstr. 74-10012249 Berlin, GermanyAbstract. Salinization of deep aquifers below salt lakes is a common phenomenon. Potentiallyresponsible hydrodynamic processes are diffusion and free convection. These processes havebeen investigated by a large number of numerical variable-density groundwater flow andtransport model studies. Mostly the density of lake- and groundwater has been computedbased on the total amount of dissolved compounds. However, the feedback mechanismsbetween chemical reactions and density driven flow are not well understood. To date only afew studies have been conducted regarding this issue. Our study extends previous modelingstudies of salt lakes coupling hydrodynamics below playas with hydrogeochemical reactionsto investigate the interrelation between brine reflux and the precipitation of evaporites withinsalt lakes and the underlying groundwater systems. For this purpose we conducted a 2Dcoupled density-driven groundwater flow and reactive transport modeling study of a closedcoastal playa basin with dry lake conditions including the aquifer of the catchment area. Forsolute input to our evaporating basin we selected seawater. In order to be able to comparethe processes of diffusion- and convection-dominated system we simulated two scenarios witha permeability of 1E-12 and 1E-14 m2, respectively. The convection-dominated system showsthe typical flow pattern with the following temporal development: (i) Brine generation startsclose to the evaporation zone, (ii) initialization of free convection (fingering) with severallocal convection cells, (iii) merging of local convection cells into one convection cell over theentire aquifer. In the diffusion-dominated system no free convection develops and masstransport into the deeper aquifer is driven by concentration gradients of the dissolvedcompounds. Regardless of the transport mechanisms the computed mineral precipitationinitiates within the evaporation boundary layer which is in agreement with observed salt crustformations on the surface of playa lakes. Additional precipitation occurs in the deeper aquiferat mixing interfaces between different waters, i.e. brine and recharge water. Results show thatvariable flow patterns control the evolution of mineral precipitation and re-dissolutionpatterns. Detailed results for calcite, gypsum, glauberite and halite will be presented.Keywords: Salt lakes, evaporation, reactive transport modeling, density driven flow, mineralprecipitation178

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONSalinization of deep aquifers below salt lakes is a common phenomenon in arid and semi-aridregions worldwide. As a consequence the already limited amount of available usablegroundwater is still more restricted. Two key processes that typically induce the salinizationare diffusion and free convection. The latter has been intensively investigated by a largenumber of numerical variable-density groundwater flow and transport model studies.Depending on the investigated aquifer system the salinity may be modified by chemicalreactions such as mineral dissolution and/or precipitation (Wigley & Plummer, 1976;Sanford & Konikow, 1989). To investigate the potential importance of feedback mechanismsbetween physical processes and geochemical reactions Freedman & Ibaraki (2002) simulatedthe effects of calcite dissolution in a mixed convective transport tank experiment. Post &Prommer (2007) defined and analyzed a numerical experiment based on the classic Elderproblem. In addition, Bauer-Gottwein et al. (2007) studied the influence of chemical reactionson the onset of free convection under islands in the Okavango Delta, Botswana. Mao et al.(2006) simulated a tank experiment in which seawater intrusion was accompanied by cationexchange.The aim of the present study was to attain a more refined understanding of the temporal andspatial patterns that characterize the hydrodynamics and geochemistry below salt lakes. Thisincludes (i) the identification of temporal and spatial varying evaporite deposition patternsand how they differ between diffusion and convection dominated systems, and (ii) theestablishment of generally valid hydraulic and hydrogeochemical prerequisites for theoccurrence of mineral precipitation below salt lakes.For the present study our investigations are restricted to dry basins, so-called playas, i.e.,systems where the evaporation is greater or equal than the sum of recharge, surface waterand groundwater inflow.2. METHODSTo simulate the density-driven flow and reactive transport processes a numerical 2D verticalmodel was set-up (Fig. 1) according to the conceptual model for a closed basin dischargeplaya (B2 in Yechieli & Wood, 2002). Recharge and evaporation rate are identical (0.1 m/y).A total time of 10000 years was simulated. To explore diffusion- and convection- controlledconditions two scenarios were simulated using different hydraulic conductivities (1E-5 and1E-8 m/s). For the initial and recharge model water seawater was chosen, as published inSanford and Wood (1991). Therefore the model configuration represents most likely a coastalor continental discharge playa fed by seawater or aerosol seawater. The simulations wereperformed using a density-driven reactive transport model coupling SEAWAT-2000(Langevin & Guo, 2006) and PHREEQC-2.18, published in Post & Prommer (2007). Thedensity calculation within this version is realized using the algorithm from Millero (2001)taking into account all dissolved species considered in the present study (Ca 2+ , Mg 2+ , Na + ,K + , Cl - , Br - , SO 4 2- and bicarbonate).179

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 1 Model domain and boundary conditions3. RESULTS AND DISCUSSION3.1 General flow patternsThe groundwater density in the initial state is uniform. Therefore the groundwater flow isdirected according to the hydraulic gradient from the recharge to the evaporation zone. In theconvection controlled system fingering initializes due to the increasing density gradient at theevaporation boundary after 2 years. After 10 years fingering is highly developed with severalconvection cells merging to only one convection cell after 50 years (Fig. 2). Over time theconvection cell expands laterally until reaching the left boundary. Therefore in the course ofconvection the brine, which is produced continuously at the evaporation boundary, spreadsover the whole aquifer (Fig. 2).depth [m]0-510 years-100 10 20 30 40 50 60 70 80 90 1001.31.21.1depth [m]0-550 years-100 10 20 30 40 50 60 70 80 90 1001.31.21.1depth [m]0-510000 years-100 10 20 30 40 50 60 70 80 90 100distance [m]Fig. 2 Simulated groundwater flow and density distribution pattern after 10, 50 and 10000 years. Density unitsare in kg/l.In the diffusion-controlled system the initially prescribed advective flux remains constant untilthe end of simulation. Convective flux can not arise due to the low hydraulic conductivity.Solute spreading is therefore controlled solely by diffusive flux. In the presented case diffusiveflux is higher than advective flux resulting in brine propagation into the aquifer.1.31.21.13.2 Evaporite precipitation patternsIn the convection-controlled case precipitation of calcite (cc), gypsum (gy), glauberite (gl)and halite (ha) occurs at the evaporation boundary, caused directly by evaporative180

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivessalinization. Under natural conditions these minerals precipitate as efflorescent crust at theplaya surface. Whereas cc and gy precipitate at the whole evaporation boundary gl and haonly precipitate at the right side representing the centre of the playa. This pattern concurswith the general concept of the bull eye structure observed in natural salt lakes. In the courseof time, however, gy and cc also precipitate in deeper, saturated zones of the aquifer belowthe central part of the playa in a zone where evaporative salinization and mixing with refluxbrine enhance the gy and cc saturation. In addition, cc precipitates by mixing of refluxingbrine and background water (Fig. 3). The reason for reaching cc saturation at these mixinginterfaces is the calcium enrichment in the brine during the brine formation at theevaporation boundary. According to the chemical divide concept, due to an initialcalcium/bicarbonate ratio > 1, the primary cc precipitation caused by evaporation leads todecreasing bicarbonate and increasing calcium concentrations in the brine, while the brineremains saturated in cc (SI=0). Owing to convective mixing, the calcium-rich brine comes incontact with background water with higher bicarbonate contents leading to cc oversaturationand precipitation in the mixing zone. Therefore this kind of cc precipitation is not primarilyassociated with evaporation.depth [m]0-520 years-100 10 20 30 40 50 60 70 80 90 1000-2-4depth [m]0-550 years-100 10 20 30 40 50 60 70 80 90 1000-2-4depth [m]0-5200 years-100 10 20 30 40 50 60 70 80 90 1000-2-4depth [m]0-510000 years-100 10 20 30 40 50 60 70 80 90 100distance [m]Fig. 3 Simulated calcite distribution pattern after 20, 50, 100 and 10,000 years (Units in mol/kgH 2 O, log scale).Though the flow pattern in the diffusion-controlled system is different, primary evaporationand secondary diffusive (not convective) mixing of brine and background water also result inadequate mineral precipitation patterns.0-2-44. CONCLUSIONSThe simulations show that at salt lakes among mineral precipitation caused by evaporationalso precipitation by convective and diffusive mixing of brine and background water occurs.The latter process is related to the chemical divide concept. That implies that mineralprecipitation at the playa surface due to evaporation of pristine groundwater, which containsevaporite-forming dissolved anion-cation pairs (e.g. calcium and bicarbonate forming cc) in181

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesdifferent equivalent concentrations, is resulting in brine with an enriched and a depletedcomponent of this pair. In principle mixing of this brine with the pristine groundwater canlead to further precipitation of the same mineral, wherever in the aquifer mixing occurs.REFERENCESBauer-Gottwein, P., T. Langer, H. Prommer, P. Wolski, and Kinzelbach, W., 2007. OkavangoDelta islands: Interaction between density-driven flow and geochemical reactions underevapo-concentration. J. Hydrol., 335, 389– 405.Freedman, V., & Ibaraki, M., 2002. Effects of chemical reactions on density-dependent fluidflow: On the numerical formulation and the development of instabilities. Adv. WaterResour., 25, 439–453.Langevin, C. D., & Guo, W., 2006. MODFLOW/MT3DMS-based simulation of variabledensityground water flow and transport. Ground Water, 44(3), 339–351.Mao, X., Prommer, H., Barry, D. A., Langevin, C. D., Panteleit, B., & Li, L. 2006. Threedimensionalmodel for multi-component reactive transport with variable densitygroundwater flow. Environ. Modell. Software, 21, 615– 628.Millero, F.J. 2001. Speciation of metals in natural waters. Abstracts of Papers of theAmerican Chemical Society, 221(1). U533-U533.Post, V.E.A., & Prommer, H., 2007. Reactive multicomponent transport simulation of theElder problem: Effects of chemical reactions on salt plume development. WaterResources Research. 43(10), W10404.Sanford, W. E., & Konikow, L. F., 1989. Simulation of calcite dissolution and porositychanges in saltwater mixing zones in coastal aquifers. Water Resour. Res., 25(4), 655–667.Sanford, W.E., & Wood, W.W., 1991. Brine evolution and mineral deposition inhydrologically open evaporite basins. Am J Sci 291 (7), 687–710.Wigley, T. M. L., & Plummer, L. N., 1976. Mixing of carbonate waters. Geochim.Cosmochim. Acta, 40, 989– 995.Yechieli, Y., & Wood, W.W., 2002. Hydrogeologic processes in saline systems: playas,sabkhas, and saline lakes. Earth-Science Reviews 58 (3–4), 343–365.182

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesLARGE-SCALE DRAINAGE MEASURES TO INCREASE FRESHWATERAVAILABILITY FROM FOSSIL SANDY CREEKSPAUW, P.S.; Van BAAREN, Esther; SANCHEZ, Marta Faneca;TANGELDER, Marijn; DEDERT, Mascha; TROOST, Karinpieterpauw85@gmail.comDeltares; Wageningen University; ImaresAbstract. The surface water and groundwater in the Southwestern part of the Netherlands arepredominantly saline. Large areas are situated well below sea level, except for the coastaldune area and fossil sandy creek deposits. The fresh groundwater that is present in the fossilsandy creek constitutes the most important source of water for the agricultural sector.However, in times of drought this amount is not sufficient to prevent crop damage. Weproposed two large-scale measures in the (conventional) drainage design (i.e. ditches anddrains) in order to increase the amount of fresh groundwater within the fossil sandy creek.One measure aims to maximize groundwater levels in the vicinity of the fossil sandy creek byremoving existing drainage. The other one is aimed at stimulating the lateral migration of thefreshwater lens by inducing preferential seepage of saline groundwater at a considerabledistance. We used the numerical code MOCDENS3D to test the effectiveness of the measureand constructed a two-dimensional model of a representative situation. We then organized aworkshop for important stakeholders in order to discuss an appropriate area forimplementation. The model was then adjusted to this location and used to calculate theincrease of the freshwater volume. Subsequently, we determined the financial consequences ofthe measurement by a societal costs-benefits analysis. Results indicate that after 30 years themeasure is more profitable compared to the autonomous scenario. Key for successfulimplementation is to secure appropriate investors, to find a way how to deal withuncertainties and to determine the participating and leading parties.183

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmMODELLING OF SALTWATER INTRUSION: A NEW FULLY COUPLED SURFACE-SUBSURFACE APPROACHJie Yang 1 ; Thomas Graf 1 ; Maria Herold 2 ; Thomas Ptak 2yang@hydromech.uni-hannover.de1 - Institute of Fluid Mechanics and Environmental Physics in Civil Engineering, LeibnizUniversität Hannover, Germany;2 - Geosciences Center, University of Göttingen, GermanyAppelstr. 9A, 30167 Hannover, GermanyAbstract. Coastal aquifers are complex hydrologic systems due to interactions between theocean and adjacent coastal aquifer such as (i) variably saturated flow, (ii) spatial-temporalfluid density variations, (iii) tidal fluctuations, (iv) storm surges overtopping dykes, and (v)surface runoff of storm water. To numerically simulate coastal flow dynamics, a coupledsurface-subsurface approach is presented. The new approach is implemented into theHydroGeoSphere model (Therrien et al. (2010)) and accounts for all processes listed above.The new approach uses the diffusive wave approximation of the St. Venant equation todescribe surface flow. Surface flow and salt transport are fully coupled with subsurfacialvariably saturated, variable-density flow and salt transport through mathematical terms thatrepresent exchange of fluid mass and solute mass, respectively. Both tides and storm surgesinduce a time-variant head that is applied to nodes of the surface domain. The approach isapplied to real cases of tide and storm surge events. Results of a tide simulation show that, inaddition to the classical salt wedge, an extra plume is formed beneath the upper part of theintertidal zone. Monitoring the exchange fluid flux rates through the beach indicates that themajor inflow to the aquifer takes place at the upper part of the intertidal zone, which explainsthe formation of the extra plume. Results also demonstrate that the extra plume ispredominantly being formed during rising tides. Results from a storm surge simulation showthat plume fingers develop below the flooded land surface. The natural remediation byseawards flowing freshwater is relatively slow. Thus, reducing the TDS concentration in theaquifer down to drinking water standards can take up to 10 years.Keywords: saltwater intrusion, coupled approach, tide, storm surge184

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmINTRODUCTIONIn coastal aquifers, flow dynamics is controlled by tidal activity and by storm surges that mayovertop a protective dyke and flood the inland. The objective of this study is to numericallyinvestigate saltwater intrusion influenced by both tidal activity and an overtopping stormsurge event. Using the numerical model HydroGeoSphere (HGS), we will adopt a fullycoupled surface-subsurface approach to investigate the combined effect of tide and stormsurge. Tide and storm surges induce a time-variant head applied to nodes of the surfacedomain. The fully coupled hydraulic interaction between the surface domain and thesubsurface domain simplifies flow and transport boundary conditions caused by tidalfluctuation or storm surge events. By investigating coastal aquifer flow dynamics with a fullycoupled approach, we are interested to see: (1) how tide circulations influence the solutedistribution in a coastal aquifer, (2) how the storm surge induces the development of saltplumes in inland aquifers, and (3) how long the system can recover from a storm surge bynatural remediation.1. MATHEMATICAL MODELHGS is a 3D numerical model describing fully-integrated variably-saturated subsurface andsurface flow and variable-density solute transport. HGS uses the diffusive-waveapproximation of the St. Venant equation for surface water flow. A variation of Darcy'sequation in terms of equivalent freshwater head is used to calculate the surface-subsurfaceflux exchange, and solute exchange is calculated in advective and dispersive form accordingto the exchange flux rate between two domains. Using the diffusive wave approximation torepresent surface flow caused by tide fluctuation and storm surge is not theoretically validbecause the diffusive wave approximation is normally only valid for inland systems where thefrictional resistance is relatively high, and where water depth and flow rates are small.However, we tried to ensure the diffusive wave approximation can be used by adopting thefollowing assumptions:(1) Flow rates on the surface in the free seawater zone are not used in our study because theyare unreliable. However, in order to control the flow rate overtopping the dyke during astorm surge, the surface friction coefficient, and thus the surface flow rate, are adjusted torepresent a realistic value. (2) Constant solute concentration boundary condition will beassigned to submerged nodes of the free seawater zone, thus getting rid of the effect fromunreliable flow rates, which will cause unrealistic concentrations in the free water zone. (3)The density effect will be neglected for both flow and transport solutions in the surfacedomain.2. SIMULATION AND RESILTS2.1 Boundary and initial conditions185

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmThe area under investigation is situated north of Bremerhaven, Northern Germany, and thechosen cross-section is positioned almost perpendicular to the coastline and is approximately12 km long. The subsurface domain is discretized by horizontal prisms, and the surfacedomain is discretized by 2D faces. Parameter values are chosen from previous work for theinvestigated site. A time-variable head representing tidal activity and a constant saltwaterconcentration are prescribed to the left sea side boundary. A time-variable head is prescribedto the left edge nodes of the surface domain, and constant concentration is prescribed to thosesurface domain nodes that are submerged by seawater. Average sea level of 0.045 m.a.s.l iscalculated based on a serial of tide records. Initial conditions are obtained by running thesimulation with the sea level of 0.045 m.a.s.l to reach steady-state.3.2 TideA period of 20 days is simulated. Results show that the tide fluctuation leads to the formationof an extra salt plume beneath the upper part of the intertidal zone (Fig.1). Results of theexchange fluid flux between the surface domain and the subsurface domain through the beachshow that the maximum exchange rates occur around the low tide and high tide coastlines.Exchange rates in the intertidal zone are relatively irregular, such that the flow-in and flowoutprocesses occur alternately along the land surface. The inflow induced by the high tideexplains the formation of the extra plume. We also performed individual analyses for the fourtide states: rising, high tide, dropping and low tide. The results also show that the exchangerates on the re-exposed part of the beach are irregular. It is also confirmed that the rising tideperiod significantly contributes to the development of the plume (Fig.1).Fig. 1 TDS concentration distribution and flow paths. The extra plume is shown in the dashedcircle.3.3 Storm surgeOne single storm surge pulse is generated in the numerical model, in which the maximumovertopping flow-in rate is limited to be less than 200 l s -1 m -1 (EurOtop (2007)) by adjusting186

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives45 mmthe friction coefficient of the land surface. In the storm surge process, a total of about 10446m -3 of saltwater flow across the dyke into the inland area behind dyke. The overtopping lastsfor 2.8 hours, and about 261 tons of salt are delivered into the inland area. Saltwater flowsacross the dyke, and then flows as far as 3 km inland. The surface water starts to infiltrateinto the unsaturated soil, thereby developing salt plumes. 3 days after the storm surge, a saltplum just behind the dyke has developed that reaches about 30 m into the aquifer, and whoseconcentration is up to 3000 mg l -1 . One month later, the deepest plume front reaches 60 minto the aquifer. Within one year, the plumes reach the bottom of the aquifer, and they start toconnect and merge laterally. 5 years after the storm surge, concentration in the aquifer hasdecreased to less than 1500 mg l -1 , and 10 years later, this value dropped to 500 mg l -1 , whichis the maximum TDS concentration for drinking water according to USEPA (USEnvironmental Protection Agency) standards. The natural remediation for salinity isrelatively slow, even after 20 years, concentration greater than 500 mg l -1 can be detected insome parts of the aquifer at a depth of about 40 m (Fig.2).REFERENCESFig. 2 Salt distributions in the domain after the storm surge[1] Therrien R, McLaren R, Sudicky E, Panday S, 2010. HydroGeoSphere: A threedimensionalnumerical model describing fully-integrated subsurface and surface flow andsolute transport. University if Waterloo and Université Laval, Canada.[2] EurOtop 2007. Wave overtopping of sea defences and related structures: Assessmentmanual. Die Küste - Archive for Research and technology on the North Sea and BalticSea coast. Kuratorium für Forschung im Küsteningenieurwesen, Volume 73, 178 pp.187

Ruben Caljé 1 ; Frans Schaars 1 ; Arjen Kok 2 188

Figure 1: Resulting depth of the freshwater-saltwater interface below Terschelling in a 3d-view, where thegrey plane marks the dividing clay layer between the second and third model layer. 189

Figure 2: The modeled interface depth and heads (background) compared to measurements (symbols).190

Figure 3: Development of the saltwater-freshwater interface by 2100 in three cross-sections with a sealevel rise of 75 cm and a change in meteorological conditions according to a warm climate scenario .191

Selected case studies

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesANALYSIS OF SALTWATER INTRUSION COMPUTATIONAL MODELINGIN RECIFE CITY (PERNAMBUCO, BRAZIL)MONTENEGRO, S. M. G. L.; PAIVA, A. L. R. de; CABRAL; J. J. S. P.;DEMÉTRIO, J. G. A.; RODRIGUES, F. B.alrpaiva@yahoo.comUNIVERSIDADE FEDERAL DE PERNAMBUCO (UFPE)Av. Acadêmico Hélio Ramos, s/n, Cidade Universitária, Recife – PE, BrazilAbstract. The problem of aquifer overexploitation in RMR (Recife Metropolitan Region)causes great concern to the scientific-technical community, managers and the population. Theapplication of State Law 11.427/1997, to conservation and protection of groundwater inPernambuco State, and the Decree Law 20.423/1998, complementing the aforementioned law,provides for the control of drillings, for the conservation and preservation of groundwater,with respect to the security of its quality and quantity. However, in the last two decades, theinsufficient water supply from public systems currently in operation, and the consequentpopulation pressure, prevent a stricter control of drilling and exploration wells to beeffective. The aquifer system of Recife (PE) is composed of two deep aquifers, Cabo andBeberibe, with semi-confined characteristics, covered by a water table one, the Boa Viagemaquifer. Recife coastal aquifers are vulnerable to degradation by salinization due tooverexploitation. Several wells in this region show increasing salt content over the years, andin some cases they have been discarded. One of the reasons stated for the salinization is themarine intrusion. The demand for fresh water has increased and in order to satisfy this need,groundwater is one of the most exploited resource. Salinization risk at regional aquifers bysaltwater intrusion has also increased. The coastal region of Recife is a plain area, itssouthern area lies next to an estuarine zone and it has high population density together withhigh concentration of wells. The high water pumping rates combined with the reduction ofrecharge rates by urban impermeabilization make this area prone to salinization problems.These problems may be caused by both by saltwater intrusion and wells constructionproblems verified in previous studies. For this research, an analysis was performed withmodeling of flow and salt transport with Modflow combined with the Seawat software.Potenciometric drawdown was verified mainly due to high pumping rates above the limitsallowed by the state agency responsible for managing water resources. Modeling resultsindicate possible saltwater intrusion.Keywords: salinization; modelling; modflow; seawat195

CONCEPTUAL MODEL OF DAR ES SALAAM QUATERNARY COASTALAQUIFER IN EASTERN TANZANIA AND ASSESSMENT OF AQUIFERVULNERABILITY TO SEAWATER INTRUSION 196

1. INTRODUCTION2. GEOLOGICAL AND HYROGEOLOGICAL ASSESSMENT3. GEOPHYSICAL SURVEY AND GROUNDWATER GEOCHEMISTRY197

198

4. CONCLUSIONREFERENCES199

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGROUNDWATER INDICATORS FOR COASTAL AQUIFERMANAGEMENT: THE URBAN CITIES OF RECIFE AND MACEIÓ, BRAZILMONTENEGRO, S.; MAIA NOBRE, R. C.suzanam.ufpe@gmail.comUFPER. Padre Landim, 302, 1401, Torre, Recife, PE, BrazilAbstract. Groundwater indicators have been used mainly to evaluate the current situationand levels of degradation, both quantitative and qualitatively. In this context, the scenario oftwo coastal urban cities are highlighted, the metropolitan Recife situated at the RecifeCoastal Plain, as well as the city of Maceio, located at the Alagoas Sedimentary Basin, bothfacing problems with water supply. Recife, the capital of Pernambuco State in northeasternBrazil, has about 1,5 millions inhabitants. Groundwater has been intensely exploited in theregion during the last years, with consumption peaks due to eventual droughts, such as the1998/99 event. In Recife, groundwater has been historically used as a complementary sourceof water. However, groundwater depletion caused by indiscriminate drilling of private wellshas been observed throughout the municipal area. Nowadays, Pernambuco State Water andClimate Agency (APAC) is responsible for groundwater management within the state. Thecity of Maceió, also located in northeastern Brazil with a population of about 900,000, relieson a coastal urban aquifer to supply approximately 70% of municipal water demands. TheWater Resources Secretariat has documented less than 50% of a total of approximately 2.000production wells, including private and public. Groundwater flow modeling has indicatedthat the existing groundwater supply system has caused excessive perturbations in thegroundwater flow regime. Salt-water intrusion, for instance, is a consequence of overpumping, and its effects have already been documented in specific areas. Therefore, specificmanagement studies are needed for both area in order to minimize interference effectsbetween wells in the system, land subsidence, salt water intrusion and problems related tocontaminated water in the cities.To assess coastal environmental processes adequately bydecision-makers, environmental indicators were applied to both cities to analyze andcompare their actual situation, based on three main lines of approach: pressure, state andresponse. This study suggests that the use of indicators has proven to be of great value forproposing protection guidelines aimed at economical, social and environmental sustainabilityof the coastal regions and constitutes an important tool for managing water resource systems,as well as for land-use planning in highly populated cities.Keywords: indicators, management, urban area200

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHYDROGEOLOGICAL STUDY FOR AQUIFER MANAGEMENT INNORTHERN STATE OF RIO DE JANEIRO - BRAZIL.SILVA Jr., G. C. da; ALVES, M. G.; MELLO, C. L; BRÊDA, T. C.; SILVA, T. A;CRISTO, V. do N.; CAETANO, P. M.; NEIVA, E. B.viniciuscristo@geologia.ufrj.brUFRJ - LAB. DE HIDROGEOLOGIA; LECIV-UENFAv. Athos da Silveira Ramos, 274 Cidade Universitária RJAbstract. Campos Sedimentary Basin, in Rio de Janeiro State offshore area, is the main oilproducer basin of Brazil. On the onshore portion of the basin, a complex aquifer systemcomposed of different layers with diverse physical and chemical characteristics occur. Theseaquifers are of enormous importance for the local population, since the withdrawal ofgroundwater is used as an alternative to the precarious regional public water supply,frequently unreliable and/or inexistant. The study area is located at about 270 km of the cityof Rio de Janeiro, in the Northern portion of Rio de Janeiro State, Brazil, with aproximately100 sq. km. area. In the region there is a shortage of hydrogeological data, except for someCPRM (Brazilian Geologic Survey) studies dating back to the 1970's and early 2000’s years,with surveying and monitoring of some pre-selected wells; data derived from test drills; andtechnical field reports. These data are acknowleged as insufficient to characterize theseaquifers. Additional studies are needed to better understanding of aquifer characteristics andcharacterization of reserves. The main objective of this hydrogeological study was tocharacterize the hydrodynamic and hydrogeochemical of Emborê formation, which occurs inthe onshore portion Sedimentary Basin of Campos and holds high potential aquifers, withellaboration of geological and hydrogeological maps; geological, geophysical andstratigraphic cross sections; depositional setting of heterogeneities aiming to characterize thereservoir and obtain stratigraphic and hydraulic parameters of aquifers. The area is beingoccupied by a series of infrastructures (ports, railway, industrial plants and humanoccupation), as well as injection of hypersaline water in deep aquifers and other potentialyenvironmentally harmful activities. The sustainable management of aquifers in the areadepends on a good understanding of aquifer characteristics.Keywords: Hydrogeological Study; Aquifer Management; Campos Sedimentary Basin201

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHYDROSTRATIGRAPHIC STUDY OF ITAIPUAÇU DISTRICT AQUIFER –MARICÁ, RJ, BRAZIL.CRISTO, Vinicius do Nascimento; SILVA Jr., G. C. da; ZELY, G.; SILVEIRA, P.viniciuscristo@geologia.ufrj.brUFRJ - LAB. DE HIDROGEOLOGIABoulevard 28 de setembro, 245 casa 6 apto 201 Vila Isabel RJAbstract. This work aims at the hydrostratigraphic characterization of Itaipuaçu district inMaricá municipality, Rio de Janeiro State, Brazil, located at about 50 km from the city of Riode Janeiro. This aquifer is important for the local population because is the only in situsource of water in the area and during the last twenty years large scale withdrawal ofgroundwater through shallow wells has increased the water stress. The overall objectiveincludes the elaboration of a preliminary hydrostratigraphic model of the coastal aquiferdescribed above. It was accomplished with the compilation of information of previous works,field campaigns and gathering of stratigraphic, hydrodynamic and hydrochemical data pluswells and mapping. The coastal area from Rio de Janeiro city to Cabo Frio, has a lagoon–sand barrier system deposited in the small plains constrained by the gneissic and graniticbedrock monoliths, typical of Rio de Janeiro coast. The Itaipuaçu district, in Maricá, presentstwo series of isolated lagoons separated by sand barrier. These sand barriers were formed intwo distinct geological events: the inner sand barrier in conditions of high sea level duringthe Pleistocene, overlain by the younger deposit corresponding to the outer sand barrier,formed during transgressive conditions in the Holocene. In the study site, it is possible torecognize an ancient depositional system with coastal environments of the barrier-lagoontype, with a series of paleochannels that fed the lagoon, now buried, located behind the outerbarrier. Interpretation of other works associated with the ongoing research, indicate that thebedrock contact with the sedimentary deposits and the inner barrier is around 3 and 4 metersdeep, while the outer barrier contact occurs at about 50-60 meters deep, depending on thestretch where it is located. Through the information obtained so far, it is possible to define ahydrostratigraphic preliminary model of the Itaipuaçu aquifer as a succession of medium tocoarse sands intercalated with thin layers of clay. Thus it was possible to elaborate ahydrogeologic model where two shallow aquifers located at different levels, the upper one toa 8-12 m depth and the lower one at 35-45 m depth, both fresh water aquifers, have a markeddifference in behavior. Between these two aquifers and beneath the lower one, a brackishwater body occurs, making it very important when considering aquifer exploitation andprotection.Keywords: Hydrostratigraphic; Barrier-lagoon type; Itaipuaçu202

GROUNDWATER SALINIZATION IN THE COASTAL AQUIFER OF RECIFE,BRAZIL 203

1. INTRODUCTION 2. HYDROGEOCHEMISTRY2.1 Analytical procedures2.2 Ionic ratios and water-rock fingerprint Samples rNa/rCl rMg/rCa rK/rNa rCl/rHCO 3 (rK+rNa+rMg)/(rCl/2)² 0,41 0,68 0,60 0,84 2,25 0,73 0,16 0,75 0,84 0,82 0,52 0,77 0,54 0,36 0,86 1,80 0,53 0,26 0,44 0,01 0,65 0,77 0,69 0,71 0,75 204

3. ENVIRONMENTAL ISOTOPES3.1 Analytical procedures 3.2 Isotopes: Groundwater evolution and salinization 205

1,61,41,210,80,60,40,20H-3 (TU)Luiz IgnácioIlha BelaMarante PlazaN. Sra CopaEncanta MoçaManibuWellN. Sra LoretoMaria YolandaMonte Sinai ACKNOWLEDMENTSVauthier206

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMODELLING THE HISTORICAL EVOLUTION OF THE FRESH-SALTWATER DISTRIBUTION IN A DUTCH-FLEMISH TRANSBOUNDARYAQUIFERVANDEVELDE, D. 1 ; KALAND, L. 2 ; LERMYTTE, J. 1; LEBBE, L. 3 ; OUDE ESSINK,G. H. P. 4 ; VANDENBOHEDE, A. 3 ; JANSSEN, G. 4 ; CLAUS, J. 3 ; D’HONT, D. 1 ;THOMAS, P. 1di.vandevelde@vmm.be1. Flemish Environment Agency2. Province of Zeeland3. Ghent University4. DeltaresVMM, Koning Albert II-laan 20, 1000 Brussels, BelgiumAbstract. Within ScaldWIN, a European project for a better quality of surface andgroundwater bodies in the Scheldt International River Basin District, a salinisation study isperformed along the Dutch-Flemish border. General aim is to predict the distribution of freshand saline groundwater in the phreatic aquifer under changing climate conditions and sealevel rise. Putting together a good and consistent data set underlying the transboundary studyis complicated by the two regions’ specific coordinate systems, typologies and densities ofdata acquisition. The transboundary nature of the study thus necessitates trade-off choicesbetween model consistency and model detail. To understand the present fresh-salt waterdistribution and to predict changes in coming decades, it is essential to investigate thebehavior of the groundwater system in the past. Modelling the historical evolution (viz. in thiscase the last 1000 years) of the fresh-salt water distribution is therefore an important aspectof the project. This historical simulation using the 3D density-dependent code MOCDENS3Dis discussed in the paper. The past 1000 years were characterized by a highly dynamiccoastal environment and by human intervention such as land reclamation. Starting with anatural coastal environment, characterized by tidal mud-flats, marshes and dunes, land wasgradually reclaimed by building dykes and developing a drainage system. This reclaimedland was regularly affected by floods and coastal erosion. Taking into account the number offloods and reclamations per century, a time discretisation is chosen. Considering differenttypes of historical data (such as medieval paintings), a landscape is reconstructed for eachstress period. A distinction is made between tidal channels, tidal mud-flats, dune belts, tidalmarshes, polders and the hinterland. For each geomorphological unit, hydraulic parametersand boundary conditions are set. The full paper will go into detail about the method for modelconceptualisation, landscape reconstruction and boundary conditions, and will present someresults of the historical modelling.Keywords: variable-density groundwater flow, historical evolution fresh-salt waterdistribution, Dutch-Flemish transboundary aquifer207

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesRELIABLE MONITORING OF FRESH-SALINE WATER INTERFACE INCOASTAL AQUIFERSLEVANON, Elad; Yechieli, Y.; SHALEV, E.; FRIEDMAN, V.; GVIRTZMAN, H.eladlevanon@gmail.comGeological Survey of Israel; Geological Survey of Israel; Hydrological Service of Israel;Hebrew University of JerusalemEdmond J. Safra campus, Givat Ram, Jerusalem, 91904Abstract. This study deals with the reliability of monitoring of the fresh-saline water interface(FSI) in coastal aquifers, considering the effect of tides in long-perforated boreholes. ElectricConductivity (EC) fluctuations at the coastal aquifer of Israel, as measured in longperforatedborehole, were found to be in the same periodicities as sea tide, but some orders ofmagnitude larger than sea level or groundwater level fluctuations. On the other hand, directmeasurements in the aquifer through buried EC sensors demonstrate very small fluctuationsin EC. This implies that EC measurements within the long-perforated boreholes might bedistorted due to a vertical flow in the borehole, while actual fluctuations of the FSI within theaquifer are some orders of magnitude smaller. This vertical flow occurs due to sea tidefluctuations – On high tides, the hydraulic head of saline water on the lower part of theborehole increases, so upward flow occurs in the borehole. On low tides, the hydraulic headof saline water decreases and induces downward flow. Fast – Fourier – Transform analysisdemonstrates that sea tide fluctuations are the driving force for water level and ECfluctuations within the borehole. Considering these field data, we suggest that monitoring offresh - saline water interface adjacent to the sea through long-perforated boreholes isunreliable. EC fluctuations in short-perforated boreholes (1 m perforation on the upper partof the FSI) were somewhat larger than in the aquifer, but much smaller than those in thelong-perforated borehole. The short-perforation diminishes the vertical flow and thedistortion and therefore more reliable for monitoring of the FSI at shoreline vicinity.Keywords: Interface; Coastal aquifer; Tide; Monitoring;208

Jennifer Klimke 1 ; Gabriele Ertl 2 ; Jörg Elbracht 2 ; Helga Wiederhold 1 209

Saltwater intrusionsAquifer partly or completely saltyOnly lower part of aquifer saltyInland salinization(saltdome leaching and rising of water)borderline pretertiary solid rock (to thesouth) and Tertiary or Quarternaryunconsolidated rock (to the north)Near surface saltdomeDenmarkHamburg(LowerSaxony)QuakenbrückHannover 210

211

U4Quakenbrück212

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSALINIZATION ASSESSMENT BY FILED INVESTIGATION ANDMODELING OF THE SHALLOW AQUIFER AT THE DOWNSTREAM OFLEBNA WATERSHED, TUNISIATARHOUNI, J. 1 ; KAWACHI, A. 2 ; TSUJIMURA, M. 2 ; TAKAHASHI, M. 2 ;CHEKIRBENE, A. 3 ; ZIADI, M. 1elmaainat@yahoo.fr1. National Agronomic Institute of Tunisia, Tunisia.2. Alliance for Research on North Africa, University of Tsukuba, Japan.3. Graduate School of Life and Environmental Sciences, University of Tsukuba,Japan.NATIONAL AGRONOMICAL INSTITUTE OF TUNISIA 1082Abstract. In coastal aquifers of Tunisia, there are several examples of indirect impact ofhuman activity on groundwater recharge and discharge. The most important cases arerelated to overexploitation of groundwater table downstream, water surface storage at thewatershed upstream and irrigation practices. In the very well known example of the Korbaaquifer in Cap-Bon peninsula (North east of Tunisia), the case of the shallow aquifer ofLebna was considered and salinization assessment was performed on the basis of filedinvestigation and modeling. Groundwater table survey and chemical analyses of surfacewater and groundwater were performed for the coastal shallow aquifer of Lebna watershed inorder to examine the effects of hydraulic management at the watershed level on thesalinization process along the shore area. Measuring the groundwater level and water qualityand collecting the water samples for analysis of inorganic solute ions were carried out in July2010 at 63 locations including private wells, the river and reservoir. According to the contourmap of groundwater table, the groundwater flow from the reservoir was found in thedownstream area of the reservoir only. On the other hand, the groundwater level around theestuary of the Lebna River was lower than the sea, thus seawater intrusion seemed to occurthere. In addition, from the results of the chemical analyses, the spatial distribution ofchloride ion concentration which is used as a tracer also showed that the reservoir waterinfiltrates the downstream area. The interpretation of these results allowed to well understandthe salinization process over the considered plain and to propose a conceptual model of flowand salt exchanges between the dam, the river, the sea and the shallow aquifer. VisualModflow Pro 4.2 Model was applied to simulate all these exchanges and to assess the futureevolution of the system. Therefore, the high salinization has been superimposed on the effectsof seawater intrusion, because of the high and increasing contents of chloride ions. However,recent investigation of this aquifer has shown that the chemical characteristics ofgroundwater are the result of others components: intruding seawater, direct cation exchangelinked to seawater intrusion and dissolution processes associated with cations exchange. Thepresence of these processes indicates that seawater intrusion is still major acting as a sourceof salinization of the groundwater in korba coastal plain.Keywords: Interface; Coastal aquifer; Tide; Monitoring;213

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSEAWAT MODEL DEVELOPMENT FOR STUDY OF SALTWATERINTRUSION AT BIG CYPRESS BASIN, FLORIDAWeixing Guo; Ke Fengwguo1@aol.comSCHLUMBERGER WATER SERVICES; South Florida Water Mangement District1567 Hayley Lane #202, Fort Myers, FL 33907 USAAbstract. Big Cypress Basin, as part of South Florida Water Management District (SFWMD),is located in the coastal area in southwest Florida, USA. As the population and water supplydemands increase in the lower west coast planning region of southwest Florida and thepotential for sea level rise remains a concern, saltwater intrusion can pose a serious threat topublic supply wells and the coastal ecosystem. Assessing the nature and extent of the potentialfor saltwater intrusion in the southwest Florida area is critical to effective future waterresources management strategies To study the potential impact due to sea level rise andincrease of groundwater withdrawal in the coastal area, a variable-density flow and solutetransport numerical model was developed using SEAWAT The model covers the westernportion of the Big Cypress Basin. The model consists of 7 model layers representing theWater-table aquifer, the Lower Tamiami aquifer and the Sandstone aquifer, as well the semiconfiningunits between these aquifers. The Lower Tamiami aquifer, the major water supplyaquifer in the area, was divided into three sub model layers in order to get better verticalresolution. Transient model calibration was performed for the time periods from January2005 to December of 2006. The results of model calibration indicates the model calculatedwater and water quality are in close agreement with field observed data. After modelcalibration, this model was used to evaluate the potential impacts of future sea level rise andincrease of pumpage of groundwater in a wellfield near coast. In the first scenario, the sealevel is expected to rise 1 foot over the next twenty years at a rate of 0.1 ft every two years.The results of model simulation indicate the saltwater intrusion will occur mainly the lowland area south of US-41. The encroachment of saltwater in the deeper aquifer is expected tobe slower and it takes longer time for the equilibrium between the freshwater and saltwater tobe established. In the second scenario, the current pumping rate at the City of Naples CoastalWellfield will be doubled in next twenty years. The simulation results clearly indicate that thesaltwater will move landward quickly in response to the increase of groundwaterwithdrawals, especially at the southern end of the wellfield where the coastal ridge is absent.Keywords: SWI, SEAWAT, Sea Level Rise214

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTHE COASTAL LABORATORY: SALT AND FRESH WATER SUPPLYVan BAAREN, E. S.; De LOUW, P. G. B.; FANECA SANCHEZ, M.;De VRIES, B. W. H.; OUDE ESSINK, G. H. P.esther.vanbaaren@deltares.nlDELTARESAbstract. The Coastal Laboratory of Het Zeeuwse Landschap (HZL) brings together three keyelements: coastal defense, food supply (aquaculture) and landscape and nature development.The planned location of this saline polder is the Dutch island Schouwen-Duiveland, boundedby the saline Oosterschelde and an agricultural saline seepage area. Agriculture is stillpossible in this area because of the fresh rainwater lenses floating on top of the salinegroundwater.; The creation of a saline polder in a relatively fresh agricultural environmentleads to some important questions: Does the construction of the saline polder lead to anincrease of salinisation, drought or water logging in the surrounding agricultural land? If so,how can we prevent or reduce this? Which water management techniques are applicable inthe design and how do they influence the water system?; This study is in cooperation with theDelta Academy and uses knowledge of research of De Louw (rainwater lenses), INTERREGIV projects CLIWAT and CPA and the groundwater model for the Province of Zeeland. Themain goal is to develop a hydrogeological instrument to predict and quantify effects of theCoastal Laboratory on the hydrogeology and salinisation of the saline polder itself and thesurrounding agricultural land. This density dependent groundwater model with coupled salttransport supports HZL with a sustainable and innovative design. To construct and verify themodel we started a monitoring campaign for the fresh-salt distribution, groundwater heads,seepage and infiltration areas and geology.; In the Coastal Laboratory we find shallowgroundwater salinities of more than 50% of seawater. The surrounded agricultural land isquite fresh; we can find fresh seepage from the dunes and small freshwater lenses. Themeasurements are used to improve the model. Based on the geological measurements, thebest geological fit from the geology scenarios is chosen. A new initial chloride concentrationis constructed and the head measurements are used for calibration of the model.; Numerousmeasures are designed in order to reach the final land-use development. The influence andeffectiveness of measures such removing a ditch, water level change or change in dewateringlevel are simulated and quantified. With this study the design of The Coastal Laboratory willbe optimized taking into account the saltwater availability for the saline polder as well as thefreshwater availability of the neighboring agriculture. withdrawals, especially at the southernend of the wellfield where the coastal ridge is absent.Keywords: nature, salt and fresh water supply, saline polder, model, measures215

Understanding of salinewater hydrodynamics in aquifers(theoretical and numerical aspects)

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA NOVEL APPROACH TO VISUALIZE THE AGE STRATIFICATION ANDINTERNAL DYNAMICS OF FRESHWATER LENSES – LABORATORYEXPERIMENTS AND NUMERICAL SIMULATIONSLeonard Stoeckl 1 , Georg Houben 1 , Hans Sulzbacher 2HULeonard.Stoeckl@brg.de1 - Federal Institute for Geosciences and Natural Resources (BGR); 2 - Leibniz Institute forApplied Geophysics (LIAG)Leonard Stoeckl; BGR; Stilleweg 2; 30655 Hannover, GermanyWe performed a series of multi-tracer laboratory experiments in a transparent sand-boxmodel to visualize (a) processes during the genesis of freshwater lenses and (b) their internaldynamics and (c) effects of changing boundary conditions (e.g. climate change). Utilizing anacrylic glass box, we were able to simulate a cross section of an infinite strip island andinvestigated processes in two dimensions on a laboratory scale. A novel approach of usingdifferent tracer colors and varying them spatially and over time within the recharge watersallowed us to visualize and measure internal flow processes. Age stratification and flow pathscould therefore be investigated. Moreover, a combination of temporal and spatial tracer colorvariation in one single experiment enabled us to measure flow velocities of freshwatermovement. For validating our model results, generation and degradation of a freshwater lenswas performed and compared to numerical simulations using FEFLOW as well as analyticalsolutions.Keywords: Freshwater lens, sand-box model, tracer dyes, FEFLOW219

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONFreshwater lenses as they occur on oceanic islands and inland around the world aregenerally the primary resource for local water supply. These vulnerable systems are prone toanthropogenic impacts as well as effects induced by climate change. The Federal Institute forGeosciences and Natural Resources (BGR), Germany, launched the research project “FLIN”- Freshwater Lens Investigation - to explore freshwater lenses on different scales, to set abaseline and to predict changes for the future. For looking at processes inside a freshwaterlens and consequently better understanding its dynamics, we set up a two dimensionalphysical sand-box model and compared these results with numerical and analytical solutions.Numerical models additionally help to upscale our findings and give a holistic view on thedynamics of real freshwater lenses on oceanic islands. Field investigations are currentlyconducted on the East Frisian Island Langeoog, where next to geophysical methods (nearsurface and aero-electromagnetics), isotopic and hydro-chemical studies are conducted.Field investigations primary aim to determine the freshwater lens dimensions andgroundwater recharge rates. Focus is set on heterogeneities in geologic and geomorphologicstructures as well as variations of spatial and temporal groundwater recharge, driving thelens dynamics.2. MATERIALS AND METHODS2.1 Sand-box modelFor laboratory scale modeling, an acrylic sand-box model with dimensions of 200 cm inlength, 50 cm in height and 5 cm in thickness was used (Fig. 1) A cross section of an infinitestrip island was simulated by filling coarse sand (grain size d = 0.7 – 1.2) into the box andsaturating the sand from bottom to top with degassed saltwater (density = 1021 kg/m³). Byrecharging the island homogeneously with freshwater (density = 997 kg/m³) from above, afreshwater lens developed. 15 individual drips were used for freshwater recharge. Bytemporal or spatial variations of different fluorescent tracer dyes like uranine (yellow), eosine(red) and indigotine (blue) in recharge waters, we were able to visualize time and spacedependent dynamics inside the lens. Coloring single saltwater spots helped to detect saltwatermovements in the vicinity of the interface (red spot in Fig. 2). All experiments were filmed andanalyzed using fast motion.While using a constant recharge rate, we performed two different types of experimental setup:(1) changing tracer colors in the infiltrating water in all recharge drips at the same time,which allowed us to visualize the internal age stratification, (2) coloring individual rechargedrips at the same time, which enabled us to visualize single flow paths through the lens and(3) a combination of both, which facilitated the measurement of freshwater flow velocitiesinside the lens. Additionally, impacts of modified boundary conditions on the fresh220

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesgroundwater reservoir of an island were investigated, e.g. climate change induced sea levelrise, shifts in precipitation patterns.Fig. 1: Sketch of the sand-box model used for 2D visualization of a freshwater lens in a crosssection of an infinite strip island.2.2 Numerical modelFor numerical modeling the finite element model FEFLOW 5.4 was used (Diersch, 2005).Therefore a trapezoidal mesh with 112,528 elements and 56,791 nodes in two dimensions wasgenerated. The sides of the model were assigned as Dirichlet (constant head) boundaryconditions simulating the ocean. The upper boundary of the mesh was assigned as Neumann(constant flux) boundary condition, allowing only freshwater to enter the model. Theunsaturated zone was not considered. Regarding the cell sizes and potential lengths of flowpaths, longitudinal and transversal dispersivities were set to 5·10 -3 m and 5·10 -4 m,respectively. The molecular diffusion coefficient was set to 10 -9 m 2·s -1 .3. RESULTS AND CONCLUSIONSOur measurements of the maximum lens thickness, dependent on the recharge rates, weresuccessfully compared to numerical simulations as well as analytical solutions (e.g. Fetter1972, Chesnaux & Allen 2007). This model validation gives us the confidence that all relevantprocesses are considered in our laboratory experiments for the homogeneous case. By theapplication of different tracer colors in our 2D sand-box model, we were able to visualizeinternal dynamics of the freshwater flow inside a lens for the first time.A temporal variation of different tracer colors revealed the age stratification as displayed inFig. 2. We could show, that all layers remain in contact with the outflow zones at all times,and older layers get displaced downwards while getting thinner and thinner over time. Thisknowledge is essential when interpreting groundwater ages of depth specific samples (e.g. byisotopes) from real islands. A spatial variation of different tracer colors, on the other side,221

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectiveswas performed by switching every second recharge drip to another color. Hence, it waspossible to investigate distinct freshwater flow paths, which were also revealed to remain incontact with the outflow zones at all times. Moreover, we were able to measure different flowvelocities of freshwater migrating from the surface through the lens to the outflow zones by acombination of the previously described spatial and temporal tracer color variations.Measuring the time and flow path length of a triple point to travel from the top of the island tothe outflow zone, we determined flow velocities that differed of at least a factor of ten,depending on the start location. It must be mentioned that observation accuracy in ourphysical model is the dominant limiting factor, which might be improved in future byincreasing the amount of recharge drips. Flow paths and travel times find their practicalapplication in the delineation of protection zones, e.g. the 50-day zone, which is intended toprevent fecal bacteria from entering a well.Fig. 2: Visualization of age stratification by temporal variation of different tracer colors(uranine, indigotine, eosine) in recharge waters.REFERENCESChesnaux, R., Allen, D.M., 2008. Groundwater travel times for unconfined island aquifersbounded by freshwater or seawater. Hydrogeology Journal, vol. 16, pp. 437–445.Diersch, H.-J.G., 2005. FEFLOW: Finite element subsurface flow and transport simulationsystem. WASY GmbH Institute for Water Resources Planning and Systems Research,Berlin, 292 p.Fetter, C.W., 1972. Position of the saline water interface beneath oceanic islands. WaterResources Research, vol. 8, pp. 1307-1314.222

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesA PRECAUTIONARY NOTE ON THE INTERPRETATION OF COASTALAQUIFER WATER LEVEL TRENDS AND WATER BALANCESMORGAN, Leanne Kaye; WERNER, Adrian D.; SIMMONS, C. T.leanne.morgan@flinders.edu.auFLINDERS UNIVERSITYGPO Box 2100, Adelaide SA AUSTRALIA 5001, Rm 237 Earth Sciences BuildingAbstract. A precautionary note on the interpretation of coastal aquifer water level trends andwater balances Leanne K. Morgan1,2*, Adrian D. Werner1,2, Craig T. Simmons1,21National Centre for Groundwater Research and Training, Flinders University, GPO Box2100, Adelaide, SA 5001, Australia. 2School of the Environment, Flinders University,Adelaide, Australia. *Corresponding author Abstract In many cases, seawater intrusioninducedinterface movements and associated changes in seawater volume are not consideredin coastal aquifer management studies. The conditions under which this simplified approachmay result in incorrect estimates of freshwater volumes and flawed interpretations of waterlevel trend analyses are not well understood. We address this gap using a simple steady-state,sharp-interface, analytic modelling approach to generate idealised relationships betweenseawater volume, freshwater volume and water levels. The results demonstrate that seawatervolume changes impart significant influence on water level trends within coastal aquiferswhen compared to the corresponding non-coastal aquifer situation, particularly within deepaquifers with high hydraulic conductivity and low net recharge. Changes in seawater volume(over an assumed timescale) were found to be significant relative to freshwater discharge tothe sea for a number of cases, especially within deep aquifers with low hydraulic conductivity,low net recharge and low water levels, at least for the idealised conditions of the analysis.These results highlight the importance of considering changes in seawater volumes withincoastal aquifer water balances. The results also demonstrate that temporal trends in coastalaquifer water levels may not provide an adequate measure of freshwater storage trends, andrather, rapid assessment of coastal aquifer condition should consider groundwater levelsrelative to the hydraulic forcing of the ocean using an appropriate equivalent freshwater headfor the ocean boundary condition. The analytic solution used for this study involves anassumption of quasi-equilibrium conditions between the water table and interface. Thisassumption was evaluated using a selection of transient simulations, and preliminary resultswill be presented.Keywords: coastal aquifer; water balances; water level trends223

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCHARACTERIZATION OF SALINITY IN DEEP AND SHALLOW WELLS INTHE MUNICIPALITY OF CAMPOS DOS GOYTACAZES/ RJ- BRAZILCHRISPIM, Z. M. P.; ALVES, M. G.; COSTA, A. N.zeliachrispim@terra.com.brUNIVERSIDADE ESTADUAL NORTE FLUMINENSE DARCY RIBEIRORUA BENTA PEREIRA Nº123 APTº 501Abstract. Campos dos Goytacazes, located in the North Region of Rio de Janeiro State/Brazil, is distinguished by its high groundwater potential which, even under specialgeological conditions, has a tendency to form good aquifers. Groundwater in this region isresponsible for supplying a large portion of the population. With the increasing demand ofwater resources due to population growth, industrial and agricultural use, groundwaterresources will be increasingly used in an uncontrolled way and there may be supplyproblems, contamination, and possibly seawater intrusion phenomenon in coastal aquifers.The worse consequence is the deterioration of drinking water supplies exploited by thepopulation individually and the city of Campos. This study aims to investigate the quality ofgroundwater in the municipality of Campos dos Goytacazes to contribute to a betterunderstanding of hydrogeological characteristics in order to assist the management of thecoastal aquifer in the study area. For this purpose, we carried out physicochemical analyzesin 16 wells in the shallow aquifer and 5 wells in the deep aquifer, was subsequentlyperformed using the classification of waters Qualigraf software. In terms of electricalconductivity, two samples were non-standard (1380 and 1490 µS / cm) and two are near thelimit (950 and 990µS / cm), where as analysis of chlorides in all samples were within therequired standard. As for the deep wells, five of the samples, we obtained the classification ofthree samples as sweet as two brackish. For the parameter electrical conductivity of fivesamples showed a value greater than 1000S/cm, indicating strong presence of salts. In theanalysis of chloride for deep wells on the same sample showed a value outside the requiredstandard. According to the results of this survey, it is possible to concluded that thegroundwater of some deep wells presented problems of salinity at a depth less than or close to100 m. Deep wells (depths of 138 m or more), do not present problems of salinity, and arevery close to the shoreline. The shallow wells showed the same characteristic of conductivityand salinity, but showed higher values when away from the coastline.Keywords: Salinity, Groundwater, aquifers, Campos dos Goytacazes224

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCOMPARISON OF 2D AND 3D SALTWATER UPCONING UNDERLATERAL FLOW CONDITIONS WITH FOCUS ON INTERMITTENTEXTRACTION; EXAMPLES USING DATA OF THE AMSTERDAM WATERSUPPLY DUNE AREA, THE NETHERLANDSJAKOVOVIC, D. a,b ; OLSTHOORN, T. N c,d ; WERNER, A. D. a,b ;KAMPS, P. T. W. J. c ; POST, V. E. A. a,b ; SIMMONS, C. T. a,bdanica.jakovovic@flinders.edu.aua. National Centre for Groundwater Research and Training, Flinders University, GPOBox 2100, Adelaide, SA 5001, Australiab. School of the Environment, Flinders University, GPO Box 2100, Adelaide, SA 5001,Australiac. Waternet, Vogelenzangseweg 21, 2114 BA Vogelenzang, the Netherlandsd. Delft University of Technology, Department of Civil Engineering, Stevinweg 1, 2826CN Delft, the NetherlandsAbstract. To date, mostly theoretical studies have been done to investigate saltwater upconingbelow pumping wells (i.e. in axisymmetric settings) and drains (i.e. in two-dimensional crosssections).Furthermore, saltwater upconing has been tested in analog and numerical models.The oldest analog 2D models are from Pennink (1915) who used a sandbox to exploretemporal patterns of saltwater below a drain. Recently, similar laboratory experiments havebeen performed by Werner et al. (2009), which were then numerically reproduced byJakovovic et al. (2011) showing good comparison between the 2D cross section and theFEFLOW model. Oswald (1998) used magnetic resonance imaging (MRI) to verify variabledensity flow models in 3D for the first time. This was done in a sandbox of only a couple ofdecimetres in size. While Oswald’s (1998) analog model with MRI is a promising tool, itseems it has not been used extensively for upconing investigations. Although upconing isencountered worldwide, exact data to verify flow and salt transport below pumping wells arevirtually absent. The Amsterdam Water Supply has measurements of a line of wells in itscoastal dune area south of Zandvoort, the Netherlands. The data were collected for the periodbetween 1924 when the wells started pumping and the end of 1970s when the wells werestopped. These data consist of discharge and yearly chloride concentration measurements inall wells. Together with the hydrogeological settings of the aquifer system these data permitupconing verification. However, measurements directly below the well screens have neverbeen taken. Nevertheless, electrical conductivity was measured in the well screens for threeyears in the early 1950s, when upconing was most severe. It was then found that salinity inseveral wells did not enter at the bottom of the screens but somewhere above the bottom.Pennink (1915) already showed that this may be due to the lateral flow effect. Olsthoorn(2010) was able to model this phenomenon in 2D. However, upconing is essentially a 3Dproblem in which water may flow around the saltwater cone, which is impossible in 2D.Therefore, we investigate 3D upconing in a lateral flow setting that is congruent to thesituation in the Amsterdam Water Supply dune area in the period from 1924 to 1957.Preliminary results indicate a vast difference between 2D and 3D results, as expected, sincethe lateral flow is captured in the 3D model. Severe salinization occurs downstream ofextraction well series, which is a generally unrecognized phenomenon. References Jakovovic,D., Werner, A.D., Simmons, C.T., 2011. Numerical modelling of saltwater up-coning:225

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivescomparison with experimental laboratory observations. Journal of Hydrology 402, 261–273.Olsthoorn, T.N., 2010. Upconing-related downstream long-term salinization and headphenomena in the Amsterdam Water Supply Dunes. June, 16-21. 21st Saltwater IntrusionMeeting (SWIM21) Ponta Delgada, Azores, Portugal. Oswald S.E., 1998. Density-driven flowin porous media: three-dimensional experiments and modelling. Ph.D. Thesis, Institute ofHydromechanics and Water Resources Management, ETH Zurich, Switzerland. Pennink,J.M.K., 1915. Grondwater stroombanen. Stadsdrukkerij Amsterdam, the Netherlands, 151pp.Werner A.D., Jakovovic D., Simmons C.T., 2009. Experimental observations of saltwater upconing.Journal of Hydrology 373, 230-241.Keywords: saltwater upconing, lateral flow, 3D modelling226

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCONSTANTLY ALTERNATING UPWARD AND DOWNWARD HEAD-DRIVEN FLOW AS MIXING MECHANISM BETWEEN RAINWATER ANDSALINE SEEPAGEDe LOUW, P. G. B.; EEMAN, S.; Van BAAREN, E. S.; OUDE ESSINK, G. H. Pperry.delouw@deltares.nlDeltares; WUR; Deltares, DeltaresPO BOX 85467, 3508 AL Utrecht, The NetherlandsAbstract. In deltaic areas with saline seepage freshwater availability is often limited toshallow rainwater lenses which are vulnerable to climate change. Under certain conditionsthe rainwater lens may become so small that saline groundwater may reach the root zone viacapillary rise, affecting crop growth. Field measurements in the south-western delta of theNetherlands showed a gradual mixing zone between infiltrating fresh rainwater and upwardflowing saline groundwater. The mixing zone is best characterized by the depth of the centreof the mixing zone Dmix, where the salinity is half that of seepage water, and the bottom ofthe mixing zone Bmix, with a salinity equal to that of the seepage water. Dmix is found at veryshallow depth in the confining top layer, on average at 1.7 m below ground level. Aregionally driven upward groundwater flow from the upper aquifer into the top confininglayer prevents the rainwater from infiltrating to greater depths which explains the limited sizeof the lenses. Mixing between rainwater and saline seepage water therefore always occurswithin the confining layer. This mixing mechanism is analyzed with the help of variousdetailed cross-sectional models of a tile drained agricultural field, constructed with Seawat.The cell size of the model was 1 by 1m with layer thickness of 0.1 m and a daily varyingrecharge as dynamic input. We analyzed the daily vertical head and flux profiles anddetermined the lens characteristics. The results showed that large vertical head gradientsdevelop which constantly change due to the interplay of upward seepage, variable rechargeand drainage of groundwater. This causes a constantly alternating upward and downwardflow at low velocities. Whether a water particle is flowing upward or downward is indicatedby the position of the vertical flow tipping point (FLTP) which is the depth where thedownward flow component meets the upward flow component. The daily varying FLTP wasdetermined from 76 different modeled cases. The annual average position of the FLTPcorresponded with Dmix and the maximum depth of the FLTP with Bmix. From this weconclude that the constantly alternating upward and downward flow at low velocities in theconfining layer is the main mechanism of mixing between rainwater and saline seepage anddetermines the position and extent of the mixing zone. Recharge, seepage flux, and drainagedepth are the controlling factors.Keywords: rainwater lens, saline seepage; mixing; vertical flow; head-driven227

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGEOLOGIC EFFECTS ON SUBSURFACE SALINITY DISTRIBUTIONS,GROUNDWATER FLOWPATHS, AND AQUIFER-ESTUARY EXCHANGEIN INDIAN RIVER BAY, DELAWARE, USAMICHAEL, Holly A.; RUSSONIELLO, C.J.; FERNANDEZ, C.; KONIKOW, L.F.;ANDRES, A.S.; BRATTON, J.F.; BANASZAK, J.F.; KRANTZ, D.E.hmichael@udel.eduUNIVERSITY OF DELAWARE; UNIVERSITY OF DELAWARE; UNIVERSITY OFDELAWARE; US Geological Survey; Delaware Geological Survey; National Oceanic andAtmospheric Administration; University of Toledo; University of Toledo101A Penny Hall, Newark, DE, 19716, USAAbstract. Salinity distributions in the coastal subsurface are a result of complex relationshipsbetween geologic features, hydraulic gradients, and fluid density differences. The interactionsbetween these factors produce groundwater flowpaths and mixing of fresh and salineporewater that can have important effects on geochemical reactions in the subsurface that inturn affect groundwater-borne chemical fluxes to estuaries and the ocean. The focus of thisstudy is to understand the effect of a sandy paleochannel buried beneath a low-permeabilityclay and peat cap on salinity distributions, groundwater flowpaths, and resulting water fluxesinto Indian River Bay, Delaware, a coastal estuary affected by eutrophication. The hydrology,stratigraphy, subsurface salinity distributions, and submarine groundwater discharge (SGD)rates and patterns were characterized at Holts Landing State Park at Indian River Bay. Aburied paleochannel and near-bottom confining beds were located with coring and offshorechirp seismic profiling. Electrical resistivity surveys and vertical porewater salinity profilesto depths of up to 17 m indicate that a zone of relatively fresh groundwater extends hundredsof meters offshore. SGD measurements from seepage meters were collected to betterunderstand discharge salinity, rates, and spatial and temporal SGD patterns. Measurementsindicate that SGD is primarily saline, and that the lowest salinity groundwater dischargesnear the shoreline in the area away from the paleochannel feature and along the submergedpaleochannel/interfluve boundary. Hydraulic head and permeability measurements inonshore and offshore wells provide information on site hydrology and temporal change. Datawere incorporated into a MODFLOW model of the Indian River Bay watershed, whichprovides a estimate of groundwater flowpaths and fresh SGD fluxes and patterns on a largescale. The watershed-scale model was used to obtain boundary conditions for a site-scalevariable-density SEAWAT model. Simulations highlight the role of geologic heterogeneity incontrolling the flow system. Results indicate that a very low value of vertical hydraulicconductivity in the cap material and a higher value of horizontal hydraulic conductivity in thechannel bed are required to reproduce observed salinity distributions.Keywords: Submarine Groundwater Discharge; Salinity Distributions; GroundwaterModeling228

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesGROUNDWATER FLOW PATTERNS ADJACENT TO LONG-TERMSTRATIFIED (MEROMICTIC) LAKEOZ, Imri; Shalev, E.; YECHIELI, Y.; GAVRIELI, I.; GVIRTZMAN, H.imri.oz@mail.huji.ac.ilGeological Survey of Israel; Geological Survey of Israel; Geological Survey of Israel;HEBREW UNIVERSITY OF JERUSALEMEdmond J. Safra campus, Givat Ram, Jerusalem, 91904Abstract. During the 20th century, the Dead Sea level has dropped by more than 34 meters asa result of anthropogenic intervention in its water balance. In order to stop the decline and tostabilize the lake water level, a project to convey seawater from the Red Sea to the Dead Seais being considered. The inflow of seawater to the Dead Sea will have a major impact on thelake structure. The mixing with the Red Sea water is expected to change the lake from aholomictic one, that overturns and mixes once a year, back to a stratified - meromictic one.To the best of our knowledge the response of the fresh-saline water interface in coastalaquifers to changes from holomictic to a meromictic lake has never been studied before.Therefore, the objective of our study is to quantitatively evaluate the configuration of thegroundwater and the flow regime within a homogenous aquifer adjacent to a stratified lake.The high density differences, which are expected to develop between different layers in theDead Sea, make it an ideal case study for such system, even though it is rarely found in othernatural systems. In the first stage of the study conceptual and numerical models weredeveloped in order to study the steady state configuration in the aquifer. The conceptualmodel provides a basic assessment of the shape and position of the interfaces between thewater bodies in the aquifer, using the basic Ghyben - Hertzberg approximation. For thenumerical model, we used COMSOL Multiphysics (FEMLAB 3.5a) in order to quantitativelyevaluate the coupled fluid and solute transport equations. The results of the conceptual andthe numerical models show that the epilimnion intrude into the aquifer as a wedge-like shape,in-between the fresh groundwater and the saline brine, and that three interfaces are formedwithin the aquifer. The first two are between the water from the upper mixed layer and thefresh groundwater and lower brine, respectively. The third interface is between the freshgroundwater and lower brine. The groundwater flow is characterized by three circulationcells which discharge to the lake along the interfaces. Sensitivity analyses to the density andthickness of the upper mixed layer reveal that only a thick seawater layer and large densitydifferences enable the intrusion of lake water and the creation of this unique groundwaterconfiguration and flow patterns. In the second stage we use a laboratory physical model inorder to validate the results of the numerical model. The results of these experiments show thesame patterns with regarded to the location and geometry of the water bodies in the aquiferunder steady state conditions. In addition, the physical model, coupled with the same scalenumerical simulations, enables us to study the transient development of such system withtime. The results of both stages can be used as a preliminary assessment for the futureconditions in the aquifer adjacent to the stratified Dead Sea.Keywords: Interface; Stratified lake; Groundwater; Modeling; Density229

Marie Perriquet 1,2 ;Tiernan Henry 1 ;Rachel Cave 1 ;Véronique Leonardi 2 ;Hervé Jourde 2 230

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ACKNOWLEDGEMENTREFERENCES234

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesHYDRAULIC HEAD EVOLUTION IN THE DISCHARGE ZONE OF THE MOTRIL-SALOBREÑA COASTAL AQUIFER (SE SPAIN): INFLUENCE OF THE RECHARGESánchez-Úbeda, J.P. 1 ; Calvache, M.L. 1 ; Duque, C. 2 ; López-Chicano, M. 1 and Crespo,F.J. 1jp353lm@correo.ugr.es1 - Department of Geodynamics, Av/ Fuentenueva s/n 18071. University of Granada. Spain.2 -Department of Geography and Geology. Øster Voldgade 10, DK-1350. University ofCopenhagen. Denmark.Abstract. Motril-Salobreña coastal aquifer (SE of Spain) presents different characteristicscompared with the surrounding coastal aquifers of the region because saltwater intrusion hasnever been detected. This situation is mainly related with a river recharge (Guadalfeo River) andthe infiltration of irrigation water. Nevertheless several recent changes are modifying these twofactors. The inputs to the aquifer are decreasing associated to anthropogenic modifications of asystem that was stable for a long time.The position of the interface has been located (the mixing zone is at 132-230 m depth) withelectrical conductivity logs of groundwater in a deep well (250 m depth), located at 300 m of thecoastline. Ghyben-Herzberg equation was applied to compare the direct measurements and thetheoretical calculations, but due to the vertical upward flow detected in the freshwater, theresults presented clear differences.The correlation of the heads in recharge and discharge sectors showed 2 flow paths in thedischarge area. Therefore the decrease of the recharge in the aquifer could lead to amodification of the current equilibrium of the salt water-freshwater contact, fast in the upper partof the aquifer and slower in the deeper sectors of it.Keywords: coastal aquifer, groundwater flow, fresh water-sea water contact, sea waterintrusion, hydraulic head.1. INTRODUCTIONThe Motril-Salobreña coastal aquifer is an exception of Mediterranean Spanish coast, due torepresents one of the 13 aquifer units of the 49 described units that are not affected by marineintrusion processes (López-Geta and Gómez-Gómez, 2007). In previous works, it was exposed itsgood situation, both quality and quantity of groundwater (Calvache et al., 2003; Duque et al.,2008; Calvache et al., 2009).However, this optimum situation is changing due to the construction of Rules dam on theGuadalfeo River, which would suppose an artificial barrier of the river recharge to aquifer, sinceit intercepts superficial and subterranean flow. In the other hand, another factor is the decrease ofthe recharge of the irrigation water because of the urbanization of agricultural land and change inthe systems of irrigation, especially dripping irrigation. Those changes would be able to cause analteration of the existing balance between saltwater and freshwater causing an advance of theinterface.235

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTwo wells were drilled in the recharge zone and 3 wells in the discharge zone, near shoreline(Fig. 1). Since November 2009 the head has been monitored with pressure transducers in bothzones simultaneously. The objective is to relate the variations of head in recharge zone versus thevariations in discharge zone at different depths.1.1 Hydrogeological settingMotril-Salobreña coastal aquifer is on the south-east of Spain, with an area of 42 km 2 . In thewestern sector is located the Guadalfeo River one of the main inputs to the aquifer (Fig. 1). Theriver discharge was 6.2 m 3 /s for the period 1971-2004 (Martín-Rosales et al., 2008), draining animportant south sector of Sierra Nevada (the catchment has 1200 km 2 ). The aquifer system isconstituted by fluvial-deltaic detrital sediments, most of them coarse with high permeability. Inthe north boundary the aquifer is limited by the alluvial aquifer of the Guadalfeo River and onecarbonate aquifer (Escalate aquifer). The south boundary is the Mediterranean Sea. The otherborders are a geological formation of schists and phyllites, that can be considered asimpermeable, which constitute also the basement. The total thickness is variable, since a severaltens of meters at the top of the aquifer to more than 250 m thick in the western sector close to thecoastline, where the highest thickness was measured.Figure 1. Location of Motril-Salobreña Coastal Aquifer, SE of Spain, Guadalfeo River and control pointsS.130 and S.40 at the discharge zone, and R.1 / R.2 at the recharge zone.1.2 Discharge zone settingFor the study of the hydrodynamic in the fresh water-salt water contact zone, 3 wells were drilledtogether, at a distance of 300 m to coastline and close to Guadalfeo River channel. The depths ofthem are 250 m, 140 m and 49 m (called S.250, S.130 and S.40, respectively). The deepest wellis screened in 11 locations, to obtain a general characterization of the discharge zone. The other 2are piezometers, screened only in the bottom, that allow us to monitor the heads of the aquifer atdifferent depths.In S.250 well, through the logging of groundwater electrical conductivity, we determine the236

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesposition of the saltwater-fresh water interface and the modifications of it during almost 3 years.The monitoring of heads showed a permanent artesian nature, with levels around 6.5 to 6.9 mabove sea level in S.130 piezometer, and between 4.6 to 5.5 m.a.s.l in S.40. The average flow is5.2 m 3 /d in S.40 and 8.6 m 3 /d in S.130.The discovered artesian condition next to shoreline indicates that the flow pattern proposed byHubbert (1940), Glover (1959) and Kohout (1964) to the contact between fresh and salt water ispertinent in this context. According to this, as the depth increases, higher equipotentials areintercepted, due to the important vertical flow components of freshwater at the discharge zone ofthe aquifer. The lithologic data obtained during the well S.250 borehole, and the fact that the riveris recharged by the aquifer at its last stretch indicate that this is an unconfined aquifer up to 140m deep at least, from here to down there are clay layers, with intercalated conglomerate layers(Duque et al., 2011), always regarding to the shoreline next to the Guadalfeo River mouth.1.3 Recharge zone settingIn the recharge zone of the Motril-Salobreña aquifer two wells were drilled, installed with fullyscreened pipe, in the Guadalfeo River channel. These are called R.1 and R.2 (54 m and 25 mdepth, respectively) and intercepted the impermeable basement. In each of them pressure andtemperature of groundwater were monitored with transducers. From pressure data the water tablewas calculated correcting the atmospheric changes. Both wells presented a high correlation withriver flow, and it is possible to detect those maximums and minimums coincided in time.2. RESULTSFigure 2 shows the head variation in a time interval (Nov-2010/Sep-2011) at recharge anddischarge sectors of Motril-Salobreña aquifer, specifically at R.1 for recharge zone and S.130 andS.40 for discharge zone.237

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFigure 2. Temporal evolution of heads in 3 control points. S.130 piezometer and S.40 piezometer at thedischarge zone, and R.1 well at the recharge zone. Time gaps are defined between R.1 and S.130 registers.Monthly accumulated River discharge is represented in vertical bars.The temporal evolution in both sectors follows a similar path, where the peaks detectedcorrespond to maximum and minimum of the aquifer recharge in this time interval. Comparingregistered heads in S.130 piezometer with R.1 well is observed a time gap regarding the rechargezone of about 30 days and 0.3 m of head oscillation. This gap is not detected in S.40, where theobserved variations are simultaneous with oscillations in R.1, but in this case, S.40 shows a lowerpiezometric level oscillation, with maximum of 0.6 m versus 1.5 m in R.1. The significantdifference in S.130 versus S.40 is mainly due to the different hydraulic potential that existsbetween them.The difference in hydraulic potential between them allows discern different groundwater flowpaths at the discharge zone. There are superficial flow lines where the variations of heads aresimultaneous with the variations in the recharge zone, up to 40 m deep at least. There are alsodeeper groundwater flow lines, with the same variations that we observed in the rechargezone, but with softer oscillation and time gap of about one month.3. CONCLUSIONSHeads in the discharge zone showed the same peaks that the recharge zone althoughthese oscillations are considerably softer and less immediate in the discharge zoneregarding the recharge zone These variations are related with changes of the aquiferrecharge, like modifications in the Guadalfeo River discharge.. However, comparing heads atboth sectors significant differences were observed. In heads measured at S.40, a directcorrelation is detected, without time gap regarding the recharge zone. In the deeperpiezometer (S.130) a similar trend was observed but with a time gap of 30 days. Thesedifferences indicate the existence of different scale flows in the aquifer, with different flow rateand residence time. The superficial groundwater flow (up to 40 m deep) is faster and with lowerresidence time and the variations are simultaneous with the recharge zone changes. The deepergroundwater flow (from 140 m onwards) is slower and with longer residence time.AcknowledgementsThis study was performed by funding from CGL2008-05016 funded by the Ministerio deCiencia e Innovación, the research group of the Junta de Andalucía RNM-369 andPostdoctoral Mobility Program Helps of the Ministerio de Educación.REFERENCESCalvache, M.L., Rubio J.C., López-Chicano M., González-Ramón A., Ibáñez S., Martín-Rosales W., Soler R., Díaz-Losada E. and Peinado-Parra T. (2003). Estado actual delacuífero costero Motril-Salobreña previo a la puesta en funcionamiento de la presa deRules (Granada, España); In: Simposio Internacional sobre Tecnología de la intrusión de agua demar en acuíferos costeros. IGME, Madrid, 77-8.238

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCalvache, M.L., Ibáñez, P., Duque, C., López-Chicano, M., Martín-Rosales, W., González-Ramón, A. and Rubio, J.C. (2009). Numerical modelling of the potential effects of a dam on acoastal aquifer in SE Spain. Hydrological Processes, 23, 1268-1281.Duque, C. (2009). Influencia antrópica sobre la hidrogeología del acuífero Motril-Salobreña.PhD thesis, University of Granada. 296 p.Duque, C., Calvache M.L., Pedrera A., Martín-Rosales W. and López-Chicano M. (2008).Combined time domain electromagnetic soundings and gravimetry to determine marineintrusion in a detrital coastal aquifer (Southern Spain). Journal of Hydrology, 349, 536-547.Duque, C., Calvache, M. L., López-Chicano, M., Pedrera, A. and Galindo-Zaldívar, J. (2011).Establecimiento preliminar de la posición de la interfase agua dulce-agua salada en elsector de la desembocadura del río Guadalfeo (acuífero Motril-Salobreña) mediantetécnicas geofísicas y registros de salinidad. Geogaceta, 50-1, pp. 75-78.Glover, R.E. (1959). The pattern of fresh-water flow in a coastal aquifer. Journal ofGeophysical Research, 64 (4), pp. 457-459.Hubbert, M. King, (1940). The theory of ground-water motion. Journal of Geology, 48(8), (PART 1), pp. 785-944.Kohout, F. A. (1964). The flow of fresh water and salt water in the Biscayne aquifer ofthe Miami area, Florida; In: Sea Water in Coastal Aquifers. U.S. Geological Survey Water-Supply Paper 1613-C, p. 12-32.López-Geta J. A., Gómez-Gómez J.D., (2007). La Intrusión Marina y su Incidencia enlos Acuíferos Españoles; In: Enseñanza de las Ciencias de la Tierra, (153) 266-273 I.S.S.N.:1132-9157.Martín Rosales, W., Duque, C., López-Chicano, M., Calvache, M. L., González-Ramón,A. and Rubio-Campos, J.C. (2008). Modificaciones recientes del régimen hidrológico en El ríoGuadalfeo (Granada); In: López-Geta, J.A., Rubio, J.C. y Martín-Machuca, M. (Eds.), VIISimposio del Agua en Andalucía. IGME, pp. 149-158.239

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesMIXING BETWEEN FRESH AND SALT WATERS AT AQUIFER REGIONALSCALE AND IDENTIFICATION OF TRANSVERSE DISPERSIVITYDAGAN, Gedeon 1 ; PASTER, Amir 21. School of Mechanical Engineering, Faculty of Engineering, Tel Aviv University,Ramat Aviv, 69978 Tel Aviv, Israel2. Dept. of Civil Engineering and Geological Sciences, University of Notre Dame, NotreDame, IN, USAAbstract: In aquifers in which freshwater flows above saltwater, a mixing layer developsbetween the two water bodies. An approximate model of the mixing layer in steady state 3Dflow, based on the boundary layer approach, was developed in the past. The approach isdemonstrated for Yarkon–Taninim basin (Israel), a Karstic confined aquifer extending over6000 km 2 in which fresh water flushes a salt water body at the bottom of the aquifer. Usinghydrogeological data and salinity data of the discharged water in the Taninim springs, theregional scale transverse dispersivity was identified by an inverse procedure. It involvedsolving numerically the fresh water flow above the interface, computation of the transitionzone and of the salinity of the discharged water and calibration of the transverse dispersivitya T . The determined value was a T =0.04 m. This is an important finding, as it is the first timethe parameter is evaluated for an aquifer at regional scale.Ref: Journal of Hydrology 380 (2010), 36–44240

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesNUMERICAL ANALYSIS OF GROUNDWATER FLOW SYSTEMUNDER THE SEABED AT HORONOBE COASTAL AREA, JAPANNaoki Kohara 1 ; Atsunao Marui 2naoki-kohara@aist.go.jp1 -Geological Survey of Japan, AIST & Nippon Koei Co., Ltd.; 2 - Geological Survey ofJapan, AISTHigashi1-1-1, Tsukuba, Ibaraki, JapanAbstract. Fresh paleo-water was discovered on the continental shelf away from a present coastline at Horonobecoastal area. It was thought that this groundwater was formed during glacial time when sea level drops by up to120 m from present sea level. Three-dimensional variable-density flow and transport modeling of Horonobecoastal area was constructed using SEAWAT 2000 of simulating multi-species solute transport and groundwaterage. These numerical simulation results were calibrated by geophysical exploration and pore water chemistryfrom coastal drilling borehole. The model showed that current extent of fresh groundwater under the seabedcannot be explained by static boundary condition, and that sea level fluctuation is significant factor on coastalgroundwater modeling. In addition, fresh groundwater under the seabed will be washed out until next glacialperiod, so its use is not sustainable and the aquifer is not safe for geological disposal.Keywords: variable-density flow, Groundwater age, SEAWAT 2000, sea level fluctuation,Horonobe1. INTRODUCTIONA rapid increase of population in the world causes growth of water demands, and this mayresult worldwide water shortage in future. Especially, in the coastal area, water resourcedevelopment becomes important because the half of the world population is concentrated inthis area. Recently, countermeasures to mitigate climate change are discussed. Coastal areais one of the promising places for disposal of high-level nuclear waste or carbon dioxidecapture and storage. Lots of development will be conducted in the coastal areas; howeverthere are a lot of uncertainties remaining to understand the hydrogeological environment inthere.There is a report that fresh paleo-water was discovered on the continental shelf away from apresent coastline in many parts of the world such as Horonobe coastal area, because recentlyinvestigation technology has been improving (ex. Uchida, 2011). That is the proof that acomplex mixing and diffusion among seawater and groundwater and meteoric water werehappened through the long-term changes of coastal environments, related to the glacialinterglacialfluctuations. Prediction of future groundwater flow environment can be betterinterpreted by the groundwater flow model of long-term behavior like a natural analog.The purpose of this study is to find out the long-term groundwater flow processes atHoronobe coastal area through the sensitivity and scoping analysis using site-scalednumerical modeling.241

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives2. METHODS2.1 Study AreaOur study area locates coastal area in the northern part of Hokkaido, Japan. An thousandmeters borehole was drilled, and core samples were taken to extract pore water. Watersample was analyzed to find contents of salt, stable isotopic ratios of hydrogen, oxygen.Electromagnetic investigation was also undertaken to obtain distribution of specificresistance to understand distribution of salt concentration comparing its concentration ofpore water. From the analysis, fresh groundwater could be found under the seabed. Classicaltheory about formulation of salt water / fresh water interface could not explain completely,and consideration of long-term geochemical process (e.g., sea level fluctuations) is needed tounderstand this mechanism.2.2 Groundwater flow modelingFigure 1. Location map of study area.Groundwater modeling was undertaken on three dimensional geological model with the finitedifference, variable-density flow and transport code SEAWAT 2000 (Guo & Langevin, 2002).Moreover, zeroth-order reactions are conducted in direct simulation of groundwater ages(Goode, 1996). The simulated area is discretised in 39 columns and 27 rows each with awidth of 2.5 km. In vertical direction the model is subdivided in 50 layers each with athickness of 0.1 km. A no-flow and no-diffusion boundary conditions were applied for thesides and the bottom boundaries. Top boundary is set Dirichlet boundary as time depend onsea level. Sea level in Japan was cyclically varied by 0 to -120 m to modern condition duringthe 120,000-year oscillations; regression periods are 100,000 years and transgressionperiods are 20,000 years (Japan Nuclear Cycle Development Institute, 2005). For initialconditions, heads at the land boundaries are applied to the top of the model and heads of theocean boundaries are zero. Salt concentrations at the top of the entire model are set at 100-%seawater salt concentration. Hydraulic conductivity varies between 10 -4 and 10 -9 cm/s, andeffective porosity varies between 0.069 and 0.215 (ex. Ito et al., 2010).242

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives3. RESULTSTransient boundary condition including sea level fluctuations could explain the extent of freshgroundwater under the seabed though static boundary condition couldn’t regardless ofhydraulic conductivity or recharge rate. Simulated salt concentration up to 1,500 metersdepth at drilling borehole becomes lower as time passes. And the decrease rate becomes sosmall that it can ignore. Simulation results after 124,000 years show a generally reasonablefit against observation data. On the other hand, simulated groundwater age is little youngerthan the prior prediction estimated by geological knowledge (Figure 2). To collect moreaccurate information, stable / radioactive isotope methods will be needed. Figure 3 shows thecross-sectional distribution about simulation result against geophysical research. It wascalculated that the amount of fresh groundwater present on continental shelf extends 20km offshore and 1 km depth, and the groundwater has younger than 100,000 year. Therefore, it waspresumed that the fresh groundwater under the seabed is washed out due to sea levelfluctuations with each cycle.Depth(m)Cl/Cl 0 01002003004005006007008009001,0001,1001,2001,3001,4001,5001,6001,7001,8001,9002,000AlluvialSarabetsuF.KoetoiF. YuchiF.WakkanaiF.Depth(m)Groundwaterage(ky) 01002003004005006007008009001,0001,1001,2001,3001,4001,5001,6001,7001,8001,9002,000AlluvialSarabetsuF.KoetoiF. YuchiF.WakkanaiF.Calculation0.000E+00y 4.000E+03y 1.240E+05y 2.440E+05y3.640E+05y 4.840E+05y 6.040E+05y 7.240E+05y8.440E+05y 9.640E+05y 1.084E+06y ObservationCalculation0.000E+00y 4.000E+03y 1.240E+05y 2.440E+05y3.640E+05y 4.840E+05y 6.040E+05y 7.240E+05y8.440E+05y 9.640E+05y 1.084E+06y PredictionFigure 2. Profile data between calculation and observation of salt concentration (Left) andgroundwater age (Right) at drilling borehole. Cl/Cl 0 means the ratio of salt concentration.Calculation results describes under the equivalent hydraulic conditions for present sea levelat each cycle.243

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives4. DISCUSSION AND CONCLUSIONSThese simulation results indicate that freshgroundwater occurs on the continental margindue to sea level fluctuations and thisgroundwater is washed out with each cycle.Transient boundary condition is also betterthan static boundary condition for evaluationof the current distribution of the groundwaterflow under the seabed. In addition, thissimulation method to evaluate groundwaterflow system under the seabed contributeseffectively research plan such as offshoreboring, electromagnetic investigation tounderstand the processes at ocean / continentboundaries. Future plan is to understand thelocal characteristics related to the volume ofgroundwater under the seabed and toconstruct the temporal-spatial map ofgroundwater under the seabed over JapanIsland.REFERENCES(1)(2)Depth(km)(3)Depth(km)(4)Depth(km)0-0.5-1.0-1.50-0.5-1.0-1.50-0.5-1.0-1.5505050606060X(km)X(km)X(km)70708080Velocity(m/year)0.208686C/C 01.000.750.500.250.000.150.100.050.00Age(ky)240Figure 3. Cross-sectional distribution map ofspecific resistivity (1) and salt concentration(2) and velocity (3) and groundwater age (4).708086180120600Goode, D. J., 1996. Direct simulation of groundwater age. Water Resources Research, vol. 32,n. 2, pp. 289–296.Guo, W., & Langevin, C. D., 2002. User’s Guide to SEAWAT: A Computer Program forSimulation of Three-Dimensional Variable-Density Ground-Water Flow. U.S. GeologicalSurvey Open-File Report 01-434.Ito, N., M. Koshigai, A. Marui, 2010. Preliminary model for simulation of groundwater flowand seawater / freshwater interface at coastal area of Horonobe, Hokkaido. Journal ofGroundwater Hydrology, vol. 52, n. 4, pp. 381-394.Japan Nuclear Cycle Development Institute (JNC), 2005. “H17: Development andManagement of the Technical Knowledge Base for the Geological Disposal of HLW”,Supporting Report 1: Geoscience study. JNC TN1400 2005-014. (in Japanese)Uchida, T., 2011. Development of electromagnetic exploration for shallow sea area. AISTToday, vol.11, n.10, pp. 22-22.244

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesREACTIVE PORE-SCALE MODELING OF SEAWATER-FRESH WATERMIXING INTERFACERAOOF, Amir; SCHOTTING R. J., HASSANIZADEH S. M.a.raoof@uu.nlUTRECHT UNIVERSITYBudapestlaan 4, 3584 CD, Utrecht, The NetherlandsAbstract. Pore scale mixing is a key process controlling the chemistry of groundwater. Poresize heterogeneities and pore connections define the degree of transverse mixing. Thequantification of such mixing and its effects on the fate of chemicals in coastal waters are stillthe subject of debate. In this study, we examine the coupling between solute transport andreaction processes to investigate nutrient transport near a hypothetical interface betweenintruding seawater and fresh groundwater. We use a Multi-Directional Pore Network(MDPN) model to study the effect of pore scale heterogeneities on mixing between fluids withdifferent concentrations. Using MDPN we discretize the continuum porous structure as anetwork of pore bodies and pore throats orientated along various directions in 3D domains.This topological property, together with a geometrical distribution of pore sizes, enables themicrostructure of porous media to be mimicked. For each pore element, transport of solute iscalculated by solving the governing mass balance equations. Chemical reactions areincorporated through coupling with a biogeochemical reactive network simulator. Averagevalues and properties are obtained by integration over a large number of pores. Results fromthis study contribute to a better understanding of the coupling and interplay between masstransfer and reaction rates based on the pore scale information. The results showed how porescale velocity together with transversal diffusion affects the reactive mixing zone width andextends it along the main flow path.Keywords: pore scale, reaction, mixing245

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSALT LOAD TO AN AGRICULTURAL CATCHMENT: SEEPAGE FLUXTIMES CONCENTRATION, OR IS THERE MORE TO IT THAN THAT?INSIGHTS FROM A MULTI-SCALE TRACER STUDYDELSMAN, J.; OUDE ESSINK, G. H. Pjoost.delsman@deltares.nlDELTARES, The NetherlandsPOBox 85467, 3508 AL Utrecht, The NetherlandsAbstract. Agriculture is an important economic driver in the coastal region of theNetherlands. Farmers rely on fresh surface water to irrigate their crops and provide waterfor their livestock. Reversed hydraulic gradients cause relict saline groundwater – infiltratedduring Holocene transgressions (Post, 2003) – to flow upwards (viz. saline seepage),negatively affecting surface water quality. Significant quantities of fresh water from the riverRhine are used to freshen the surface water system and make the surface water suitable forfresh water use. The sustainability of this (expensive) water management practice isthreatened by climate change, as the need for fresh water increases, while its availability isprojected to decrease. Effective adaptation measures would benefit from more insight into thespatial and temporal variation of the outflow of saline seepage to surface water. However, tenyears after Sophocleous’ (2002) assertion that “quantification of water fluxes […] betweengroundwater and surface water is still a major challenge”, mechanisms that control theoutflow of saline seepage are still poorly understood. A combination of tracer-basedtechniques was used to investigate the complex interaction between saline seepage, freshwater intake, meteorological forcing and water use on the water balance of a 10 km2agricultural catchment in the coastal region of the Netherlands. These techniques range fromlow-temporal, high spatial resolution (EC measurements at a 1 m spatial resolution duringboth a wet and a dry period) to high-temporal, low spatial resolution (continuous waterquality and EC measurements at the catchment outlet). As an in-between, water qualitysamples were taken at various locations in the catchment at monthly intervals. Tracerconcentrations were converted to end member contributions (cf. Hooper, 2003) in anuncertainty analysis framework. Preliminary results show highly variable contributions ofsaline seepage to surface water, both in space and time. Observed patterns could be linked togeohydrological features of the catchment, catchment history or water management practice.The results shed light on the role of buffering in both the groundwater and surface watersystem and contribute to sustaining future fresh water availability in coastal regions.Keywords: salt load; saline seepage; multi-scale tracer; Netherlands; polder246

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSIMULATION OF HIGH-CONTRAST DENSITY-DRIVEN TRANSPORTEric Zechner 1 ; Peter Huggenberger 1 ; Ali Zidane 1,2 ; Markus Konz 1,3 ; Anis Younes 2eric.zechner@unibas.ch1 - Department of Environmental Sciences, University of Basel, Switzerland; 2 - Laboratoryof Hydrology and Geochemistry, CNRS, University of Strasbourg, France; 3 - RiskManagement Service, Zurich, SwitzerlandBernoullistrasse 32, CH-4056 Basel, SwitzerlandAbstract. Subsaturated groundwater in contact with evaporitic rock formations results inrapid subsurface dissolution or subrosion of evaporites. The process leads to both karstdevelopment and salinization of aquifers with high fluid density contrasts. To address theproblem, results of experiments and modeling approaches are presented, including: (1) acombination of flow tank and modeling experiments to study the effect of density-driven flowin heterogeneous media, and (2) a series of 2D density-coupled solute transport simulationsalong an approximately 1000-m long and 150-m deep 2D cross section, which represents asetup of two aquifers connected by subvertical normal fault zones. The resulting highcontrasts in groundwater density were simulated at both laboratory and field scale with anumerical model based on Mixed Finite Elements for the fluid flow problem and acombination of Discontinuous Galerkin Finite Element and Multi-Point Flux Approximationmethods for the transport. The experimental flow tank data are presented as benchmarkproblems to evaluate numerical codes. Simulation results of the 2D field scale cross sectionindicate that the upconing process of saline groundwater from a lower aquifer into the mainaquifer occurs under different distributions of subsurface parameters and hydraulic boundaryconditions. The simulations also revealed that the salt dissolution rate is tightly related to thestructure or dip of the halite formation, with an increase of dissolution rate with increasingdip. As a result of the increased density of the brine, an independent flow dynamic developsthat follows the direction of the dip.Keywords: Density effects, Numerical flow and transport model, Evaporites, Salinegroundwater247

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives1. INTRODUCTIONSimulation of saltwater transport is an essential tool to understand environmental problemssuch as saltwater intrusion in coastal aquifers, landfills leakage, radioactive disposals in saltrock formations and subsurface dissolution of evaporites. Subsaturated groundwater incontact with evaporitic rock formations results in rapid subsurface dissolution or subrosion ofevaporites. Depending on the geological setting the subrosion may cause widespread landsubsidence. A crucial point is to understand the role and pathways of water subsaturated withNaCl, or CaSO 4 and its driving energy, such as provided by a hydrostatic head differences, ordensity gradients, which causes groundwater to flow through the system. The mixing of highlyconcentrated brines with freshwater results in high density contrasts, which pose a challengefor efficient numerical simulation.2. LABORATORY SCALE EXPERIMENTS OF VARIABLE DENSITY FLOWA series of 2D laboratory-scale porous media tank experiments were conducted to studydensity driven flow problems based on well-defined experimental parameters and boundaryconditions. The experiments were carried out in a flow tank with a geometrical setup of twohorizontal aquifers connected by one vertical zone (Fig. 1), which represents a conceptualmodel of the investigated field scale structures (see next chapter). A photometric method wasused to study the temporal and spatial plume evolutions (Konz et al., 2008). This method issuitable for deriving isolines for 2, 10, 50 and 80% salt concentration with appropriateaccuracy. The temporally high-resolution image analysis technology facilitated theassessment of breakthrough curves (BTCs) at relevant positions in the tank.The comparison of saltwater and freshwater experiments with equal flow boundary conditionsdemonstrated the value of the experiment as a benchmark for density-coupled models (Konzet al., 2009). The experimental salt plume displayed little dispersion at all observation points.Therefore, the comparison of simulated versus measured BTCs is very sensitive to numericaldispersion and enables a reliable assessment of the codes.Numerical simulations were performed with a robust numerical model based on Mixed FiniteElements (MFE) for the fluid flow problem and a combination of Discontinuous Galerkin(DG) and Multi-Point Flux Approximation (MFPA) methods for the transport. Goodagreement was obtained for isolines and BTCs at different points using a mesh of 8000elements, and even specific patterns of the isolines were well reproduced (Fig. 2). Thesimulation with a variant of the code using the FV method instead of DG on a finer mesh of20000 elements accurately reproduced the 50% isoline. However, due to numerical diffusion,large inaccuracies are obtained for the 2 and 10% isoline and BTCs. This shows the necessityto use robust numerical schemes for the simulation of density-driven flow problems and, atthe same time, highlights the quality of the very detailed experiments for benchmarkingnumerical codes.248

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 1: Flow tank (left) with setup for 2D benchmark experiments comparing tracer and density-drivensaltwater transport in porous media after 18, 25, and 75 min duration of the experiment.Fig. 2: Evaluation of codes for 2D density-coupled simulation of benchmark experiments (BTCs left,and location of 2% (C/Cmax) isolines right).3. 2D FIELD SCALE SIMULATIONS OF HIGLY VARIABLE DENSITYTRANSPORTThe effects of increased hydrostatic gradient due to both groundwater withdrawal and fluiddensity contrasts were evaluated with a series of 2D density-coupled solute transportsimulations along an approximately 1000 m long and 150 m deep 2D cross section (Zechneret al., 2011). Simulation results indicate that the upconing process of saline groundwater intothe main aquifer occurs under different distributions of subsurface parameters and hydraulicboundary conditions (Fig. 3). For the presented setup the simulations also revealed that themost sensitive factor for the dissolution rate is the structure or dip of the halite formation,which leads to an increase of dissolution rate with increasing dip. Due to the increaseddensity of the brine, an intrinsic flow dynamic develops following the direction of the dip.The effect of variable permeability, which is due to fracture opening in the evaporitic rockformation, is simulated with a discrete fracture approach, which includes small fractures andbedding partings of a karstic, or fissured aquifer directly into a porous flow model. Thefracture aperture, or void opening, is time-dependent and a function of salt dissolution. Theresults demonstrate that the total dissolved mass with time-variable permeability is more than25% larger compared to the dissolved mass with constant permeability. The effect of the249

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesnormal fault zone thickness of higher permeability is studied by simulating fault zonethicknesses between 10 cm and 40 m. The corresponding simulated dissolution rates sharplyincrease with fault widening before they apparently start to level out at 40 m. Finally, therange of the unknown lower aquifer thickness above the rock salt ranged from 10 cm to 10 m.Simulated density-driven flow velocities are directly related to the imposed aquifer thickness:if the lower aquifer thickness decreases, then the flow velocity will increase, which leads tomore dissolved salt, and vice-versa.Fig. 3: Field scale cross-section with simulated NaCl concentration from 2D density-coupledtransport model after 30 years. Lower boundary represents saturated saltwater conditions.4. CONCLUSIONSThe experimental flow tank data of variable density induced flow was used as benchmarkproblem to evaluate numerical codes. The code based on Mixed Finite Elements (MFE) forthe fluid flow problem and a combination of Discontinuous Galerkin (DG) and Multi-PointFlux Approximation (MFPA) methods for the transport performed very efficiently. The testedcode was used to simulate mixing of highly concentrated brines with freshwater results in a2D field scale cross section. The simulations over 30 years showed that the upconing processof saline groundwater from a lower aquifer into the main aquifer occurs under differentdistributions of subsurface parameters and hydraulic boundary conditions.REFERENCESKonz, M., Ackerer, P., Meier, E., Huggenberger, P., Zechner, E. & Gechter, D., 2008. On themeasurement of solute concentrations in 2-D flow tank experiments. Hydrol. Earth Syst.Sci., vol. 12, pp. 727-738.Konz, M., Ackerer, P., Younes, A., Huggenberger, P. & Zechner, E., 2009. Two-dimensionalstable-layered laboratory-scale experiments for testing density-coupled flow models.Water Resour. Res., vol. 45: W02404, doi:10.1029/2008WR007118.Zechner E., Konz M., Younes A., & Huggenberger P., 2011. Effects of tectonic structures,salt solution mining, and density-driven groundwater hydraulics on evaporite dissolution(Switzerland), Hydrogeology J., vol. 19, pp. 1323-1334, doi:10.1007/s10040-011-0759-5.250

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSOURCES OF SALINITY IN THE QUATERNARY SAND AQUIFER OF DAR-ES-SALAAM, TANZANIAMJEMAH, I.C. 1 ; MTONI, Y. 2 ; ELISANTE, E. 1 ; TUNGARAZA, C.T. 1 ; MTAKWA,P.W. 1 ; WALRAEVENS, K. 3ichikira@yahoo.com1. Sokoine University of Agriculture, Morogoro, Tanzania2. National Environment Management Council (NEMC), Dar es Salaam, Tanzania3. Laboratory for Applied Geology and Hydrogeology, Geological Institute, GhentUniversity, BelgiumP. Box 3038 Morogoro, TanzaniaAbstract. Groundwater first started to be used as a source of water supply for the Dar-es-Salaam City in 1943. However, many of the existing boreholes in Dar-es-Salaam were drilledin 1997 after Tanzania experienced a severe drought; since then groundwater use in the cityshows an increasing trend and currently over 50 percent of residents in Dar es Salaam Cityrelies on groundwater supply. Today, there are more than 10000 boreholes for domestic,water supply and industrial purposes. Demand and reliance on groundwater from a growingpopulation along the coast raises the need to increase efforts to protect and manage theresource. In the coastal aquifer of Dar-es-Salaam, groundwater quality is influenced byvarious potential sources of salinity that determine the composition of water extracted fromwells. The results show that the origin of salinity in the area is strongly influenced by:groundwater ascending from deep marine Miocene Spatangid Shales through faults,saltwater intrusion on the border of the Indian Ocean, and throughout, there is some salinitywithin the Quaternary aquifer, especially in intercalated deltaic clays in the fluviatiledeposits, showing some marine influences. Finally, also anthropogenic pollution mayincrease the groundwater salinity. For water points where water resistivity logs and VESwere available, the freshwater-saltwater interface depth ranges between approximately 7 mand 12 m. The dominant water type is mostly NaCl with pH < 7 in both aquifers (i.e. upperand lower) except for the shallow wells where CaHCO3 prevails with pH >= 7, andboreholes located near the Indian Ocean, where coral reef limestone deposits are located andthe water type evolves towards CaHCO3. In the lower aquifer, Cl- is higher than in the upperaquifer.Keywords: Tanzania; Dar-es-Salaam; Aquifer; Quaternary; Water type; Salinity251

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSTUDY ON INTRUSION POSSIBILITY AT CAMBOINHAS COASTAL AREAMARTINS, Aderson Marquesaderson.martins@gmail.comDRM/SERVIÇO GEOLÓGICO DO ESTADO RJRUA MARECHAL DEODORO 351 CENTRO NITEROI RJAbstract. Study on possible seawateer intrusion at Camboinhas coastal area A hydrogeologicstudy is presented aiming the groundwater management of Camboinhas Beach resort inNiterói– RJ, Brazil. Groundwater budget and determination of aquifer properties werecarried out, including a flownet constructed from water table monitoring to locate rechargeand discharge areas, which constituted the starting point of the study. Properties of porousaquifer were obtained from grain-size distribution curves, porosity and specific yielddeterminations of sediment samples from shallow and deep wells and trenches. Investigationof salt water interface was carried out through electrical resistivity soundings and electricalconductivity determinations of water from wells in the coastline. Well logging andgeotechnical sounding data were used to define the aquifers boundary conditions. Calibrationof model results compared to observed data leads to put to question overexploitationhypothesis. Surplus may come from recharge contribution from fractured aquifer or fromoverlying soil cover. It is suggested further research to define safe yield extractions, in orderto prevent overexploitation and sea water intrusion. Artificial recharge and measures againstimpermeabilization increase are recommended.Keywords: SALINE INTRUSION,252

Frans W. Schaars 1 ; Mark Bakker 2 ; Joseph D. Hughes 3 Christian D. Langevin 4 253

1. INTRODUCTION2. EXAMPLE: UPCONING THROUGH AQUITARDS254

Figura 1255

REFERENCES256

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesTHE IMPACT OF HETEROGENEITY ON SEAWATER INTRUSION UNDERPUMPING CONDITIONSPOOL, María; Carrera, J.maria.pool@idaea.csic.esGHS, INSTITUTE OF ENVIRONMENTAL ASSESSMENT AND WATER RESEARCH,CSICJordi Girona 18, 08034 BarcelonaAbstract. We study the effects of heterogeneity in the hydraulic conductivity field on the 3Ddynamics of seawater intrusion in coastal aquifers under pumping conditions. A confinedcoastal aquifer of infinite areal extent with a fully penetrating well was considered. The effectof heterogeneity on seawater intrusion was studied by generating several sets ofheterogeneous hydraulic conductivity realizations. Three-dimensional simulations of densitydependent flow and solute transport were carried out on each of these hydraulic conductivityfields by increasing gradually the constant pumping rate at the well initially under nonpumping,steady state conditions. For each test, the pumping rate is constant until steadystate. In order to investigate whether the mean behavior of this setup can be approximated bya homogeneous equivalent medium we analyze models result in terms of two variables ofinterest: the dimensionless salinity at the well and concentration distribution in the plane thatcontains the well. The ensemble salinity at the well of the heterogeneous realizations and theensemble of concentration distributions were compared with the solution of the homogeneousequivalent medium to evaluate which effective flow and transport parameters provide asatisfactory representation of the mean behavior of seawater intrusion under pumpingcondition in heterogeneous media. Our numerical results indicate that: (1) the ensemble ofconcentration distributions was approximated adequately with the anisotropic effectivepermeability value, (2) the appropriate longitudinal dispersivity for the problem correspondsto the local dispersion coefficient and (3) the optimal effective transverse dispersivity toreproduce the ensemble salinity at the well depends on the pumping rate at the well.Keywords: Heterogeneity, coastal aquifer, seawater intrusion, variable-density flow, effectivedispersion257

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Figure 1. Computed density and moles versus residual fraction of evaporating seawater 260

Figure 2. Computed density and moles versus residual fraction of evaporating seawaterconsidering redox reaction 261

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22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesAddendum263

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSOURCES OF SALINITY IN THE QUATERNARY SAND AQUIFER OF DAR-ES-SALAAM,TANZANIAMjemah, I.C. 1 *, Mtoni, Y. 2 , Elisante, E. 1 , Tungaraza, C.T. 1 , Mtakwa, P.W. 1 and Walraevens, K. 3*Email: ichikira@yahoo.com1 Sokoine University of Agriculture, Morogoro, Tanzania2 National Environment Management Council (NEMC), Dar-es-Salaam, Tanzania3 Laboratory for Applied Geology and Hydrogeology, Geological Institute, Ghent University, BelgiumP. O. Box 3038 Morogoro, Fax: +255 23 2603404; Mob. +255 782 572760Abstract. Groundwater first started to be used as a source of water supply for the Dar-es-Salaam City in1943. However, many of the existing boreholes in Dar-es-Salaam were drilled in 1997 after Tanzaniaexperienced a severe drought; since then groundwater use in the city shows an increasing trend andcurrently over 50 percent of residents in Dar-es-Salaam City relies on groundwater supply. Today, thereare more than 10000 boreholes for domestic, water supply and industrial purposes. In the coastal aquifer ofDar-es-Salaam, groundwater quality is influenced by various potential sources of salinity that determine thecomposition of water extracted from wells. The results show that the origin of salinity in the area is stronglyinfluenced by: groundwater ascending from deep marine Miocene Spatangid Shales through faults,saltwater intrusion on the border of the Indian Ocean, and throughout, there is some salinity within theQuaternary aquifer, especially in intercalated deltaic clays in the fluviatile deposits, showing some marineinfluences. Finally, also anthropogenic pollution may increase the groundwater salinity.Keywords: Dar-es-Salaam; Aquifer; Quaternary; Water type; Salinity1. INTRODUCTIONThe coastal aquifer of Dar-es-Salaam has undergone a startling economic development over the past 15years after a severe drought hit the country in 1997. Many of the existing boreholes in Dar-es-Salaam wereconstructed during this period (Mjemah, 2007). Today, there are more than 10000 boreholes for domestic,water supply and industrial purposes (Mtoni et. al., 2011). Potable groundwater salinity has become aproblem of great concern in the Dar-es-Salaam City. There are several sources of salinity in the area, but themajor one is due to seawater intrusion. For water points where water resistivity logs and VES wereavailable, the freshwater-saltwater interface depth ranges between approximately 7 m and 18 m with anaverage of 12 m. The dominant water type is mostly NaCl with pH < 7 in both aquifers (i.e. upper andlower) except for the shallow wells where CaHCO 3 prevails with pH >= 7, and boreholes located near theIndian Ocean, where coral reef limestone deposits are located and the water type evolves towards CaHCO3.In the lower aquifer, Cl - is higher than in the upper aquifer.2. STUDY AREA DESCRIPTIONThe study area is located in the eastern part of Africa continent at the coastal area of Tanzania. It is locatedat latitudes 6°44’S and 7°00’S; longitudes 39°00’E and 39°19’E, with an area of about 700 km 2 (Figure 1).Geologically, the study area comprises three major parts: the central coastal plain with Quaternaryfluviatile-deltaic sediments, the deltaic Mio-Pliocene clay-bound sands and gravels in the northwest andsoutheast and the Lower Miocene fluviatile sandstones of Pugu Hills in the west of the study area. TheQuaternary deposits of Pleistocene to Recent periods have total thickness of approximately 150 m withinDar-es-Salaam City area. The overlaying deltaic deposits of Mio-Pliocene age have a thickness around 1000m (Kent et al., 1971) and are considered as the base of the groundwater reservoir.264

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesUGANDA Lake VictoriaKENYARWANDAStudy AreaMara0 150 300504000513000522000531000Indian OceanBURUNDIZAIRELakeTanganyikaMwanzaShinyangaKigomaTaboraRukwaZAMBIAMbeyaMALAWILakeNyasaArushaDodomaSingidaIringaTangaMorogoroKilometersKilimanjaroLindiPwaniMtwaraZanzibarDar-es-SalaamIndian OceanMOZAMBIQUE7 0 7KilometersCLAY-BOUND SANDSPUGU SANDSTONESCOASTAL PLAINFig. 1 Geographical and geological situation of the study areaCLAY-BOUND SANDS9252000924300092340003. METHODSA total of 300 boreholes were visited since 2004 to 2011 and electrical conductivity (EC) was recorded forproduction of EC map (Figure 2). Fifty groundwater samples were analysed for major cations and anions.The analytical methods for the above-mentioned major ions are provided in the Laboratory Manual and inStandard Methods for Examination of Water and Wastewater (APHA, 1985). The extent of marinecontamination in the aquifer (freshwater/saltwater interface depth) is determined through resistivity loggingconducted between December 2011 and January 2012.4. RESULTS AND DISCUSSIONFigure 2(a) shows the spatial distribution of salinity in Dar-es-Salaam aquifer, which is contributed bydifferent sources of salinity (ref. Figure 3). The electric conductivity log for a Gymkhana borehole as shownin Figure 2(b) demonstrates that the EC increases with depth; and it is highly saline in the depth of morethan 18 m with EC >10000 µS/cm.265

Depth (m)22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives925200092430009234000Legend:Non-saline (10000)Borehole locationsMain RiversMain Roads49Normal FaultsMsimbazi RiverKizinga RiverMzinga River38Kisarawe37(a)1Pugu HillChanikaMbezi RiverMorogoro RoadMikocheni50Bagamoyo Road36Msasani35Nyerere RoadKilwa RoadIndian OceanMasaki34Oysterbay47Gymkhana4833Magogoni304529 27TabataSegerea28 42 14 1618202126Kinyerezi41 725 10 12 13 151117 1935 96 4 8 3139 2 40 43Mbagala2423 224432Chamazi10 0 10 Kilometers01234567891011121314151617181920212223242526272829(b)EC(µS/cm)0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000Fig. 2 (a) EC (in µS/cm) distribution;boreholes with numbers used for majorions analysis(b) EC log at Gymkhana Club boreholelocated 200 m from the Ocean showingthe freshwater/saltwater interface504000 513000 522000 531000 540000Figure 3 shows two distinct groups for this data set. The CaHCO 3-type of water found at the left hand edgeof the plot, is a young groundwater from the shallow wells (samples 39, 40 and 43). The second group isfound in the right hand corner of the plot and comprises three end members. The 1 st end member isrepresented by long residence water, as evidenced by the Daru Spring (sample 37) and wells 1, 2, 29 and 30;this end member is NaCl - to NaMgCl-type water with high salinity. This water type is contributed byascending saline water through faults probably from deep marine Miocene Spatangid Shales (Mjemah,2007). The 2 nd end member comprises the fresh NaCl water, which has infiltrated on the higher terraces(samples 4, 5 and 27). The 3 rd end member is caused by saline intrusion from seawater near to the IndianOcean represented by samples 20, 21, 35 and 36. At the middle part of the Piper diagram shows influencecontributed by the occurrence of coral reef limestones. The arrow pointing to the right hand corner of theplot shows the shifting direction of the shallow wells as they become polluted. The arrow pointing to the lefthand corner shows the shifting of unconfined boreholes after contacting the coral reef limestones, wherecalcite dissolution takes place.266

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives604020Shallow wells4340Mg3980Cl + SO4Na + K6080NaMgCl-type181933138060Cla + Mg29403712 30 4 203222 5 3520 2714 21 36Samples influenced bycoral reef occurenceHCO3Legend:Shallow wellsBH (Unconfined)BH (Semi-confined)Daru SpringNaCl - EndmembersSO4806040402020Ca80 60 40 20 20 40 60 80Na HCO3 ClFig. 3 Piper diagram showing the watertypes and shifting in ion composition due to pollution5. CONCLUSIONThe origin of salinity in Dar-es-Salaam aquifer is strongly influenced by: groundwater ascending from deepmarine Miocene Spatangid Shales through faults and saltwater intrusion on the border of the Indian Ocean.The freshwater-saltwater interface depth ranges between approximately 7 m and 18 m in the area alongIndian Ocean (

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesAQUIFER STORAGE RECOVERY, THE STORAGE TANK METHODCan the Storage Tank method increase the recovery efficiency?B. des Tombe 1 ; M. van Ginkel 12 ; T.N. Olsthoorn 13B.F.destombe@student.tudelft.nl1 University of Technology, Delft, the Netherlands2 Royal Haskoning, Rotterdam, the Netherlands3 Waternet, Amsterdam, the NetherlandsDelft University of Technology - Hydrology, PO box 5048, 2600 GA DelftAbstract. A new method to store fresh water in a saline aquifer is presented. The buoyancy of injected freshwater in a saline aquifer, caused by the density difference between the two water types, usually has anegative influence on the recovery efficiency of ASR-systems in saline environment. This study, however,shows how this buoyancy effect can be used to keep the fresh water in place. We suggest using verticalbarriers partially embedded into a saline aquifer to create a subsurface tank in which the fresh water ishorizontally locked, on top of the saline water below functioning as the tank’s variable bottom. Wecombined laboratory-scale experiments and numerical modeling to study the dynamic behavior of thissystem, where the laboratory model was used to verify the numerical model and the latter to investigate theinfluence of the width, depth and aquifer characteristics on the recovery efficiency, which increases withsuccessive cycles. The technique seems promising and is especially applicable in shallow saline water-tableaquifers for the small-scale storage of rainwater or treated waste water below parks or arable land.Keywords: Aquifer Storage Recovery, variable density, subsurface barriers, coastal aquifersINTRODUCTIONASR. The storage of fresh water in aquifers for later recovery and use (Aquifer Storage and Recovery, ASR)is becoming more and more important for seasonal or emergency storage, especially in the light of climatechange and increasing population in coastal zones.Storage Tank. In areas with shallow saline aquifers the Storage Tank may be used for the storage of freshwater. We suggest using vertical subsurface impermeable barriers partially embedded into a saline aquiferto create a subsurface tank in which the fresh water is horizontally locked, on top of the saline water belowfunctioning as the tank’s variable bottom. The impermeable barriers are constructed of sheet piles, clay orother types of impermeable material. Due to the density difference between fresh and salt water, the freshwater will float on top of native salt groundwater. Mixing will only occur on the interface of these watertypes, creating a mixing zone. In this way, a subsurface fresh water tank is created which is useful to copewith fluctuations in demand and supply during the different seasons of the year and to have the requiredvolume of fresh water for emergency situations.METHOD AND MATERIALNumerical analysis. We simulated the functioning of the Storage Tank by means of the SEAWATcomputer code (Guo and Langevin, 2002) which allows for transport of water with varying density. Theopen-source groundwater modeling environment MfLab build number 340 was used (Olsthoorn, 2011). Thenumerical model was used to investigate the influence of the width, depth and aquifer characteristics on therecovery efficiency. In addition, experiments on a laboratory-scale were executed to verify the numericalmodel. We used the same characteristics for the numerical model as in the laboratory setup.268

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesLaboratory Setup. The setup is a 100x10x17 cm box filled with glass grains with a diameter of 400-600micron. The effective porosity is 38% and the horizontal conductivity is 22000 cm/day.Figure 1. Experimental model setupFresh water is stored at the left. The impermeable barrier is located at a distance of 35 cm from the left andhas a depth of 12 cm below surface-level. For injection and extraction of fresh water a gutter was placed atthe top left corner of the box. A constant head boundary at the right hand side was constructed by placing animpermeable barrier at 1 cm from the side. We kept a constant head by continuously extracting or addingsalt water at this point in the same capacity as fresh water was added or extracted. A green fluorescent tracer(fluorescein sodium salt) was added to the fresh water. UV-illumination was used to improve the contrast.The density of the fresh water with tracer was 1004 kg/m3 and the density of the salt water was 1075kg/m3. Fresh water was injected for 75 minutes, at a rate of 15 ml/min, followed by a storage period of1240 minutes. Thereafter, fresh water was extracted again by pumping via the gutter for 48 minutes at a rateof 15 ml/min. The behavior of the mixing zone was compared to numerical model, to validate the numericalmodel.RESULTSThe results show that it is possible to store fresh water in a saline aquifer between vertical subsurfaceimpermeable barriers. The numerical modeling indicates that a recovery efficiency of 30% is achievable inthe lab-scale configuration during one cycle. Because of the relatively huge thickness of the mixing zonecompared to the fresh volume in stock in the lab-scale configuration, we may expect higher recovery ratesin real-case aquifer scenarios.Cycled Operation. In cycled operation, the recovery of subsequent cycles increases, mainly due to the initialloss, which should rather be regarded as an investment in ‘salinity walls’ (i.e. Kumar and Kimbler, 1970;Merrit, 1986; Pyne, 1995). The mixing zone may be considered a pre-investment, as it kind of preventslosses in future cycles due to reduced salinity gradients. Our numerical modeling results show that therecovery efficiency increases from 30% in the first cycle to more than 70% in the fifth cycle in the lab-scaleconfiguration.Comparison numerical and experimental results. There are some small differences between the results ofthe experimental and numerical model. The flow lines in the Storage Tank during recovery differ slightlydue to the flow to the gutter. Because there are no grains in the gutter in the experimental setup, more water269

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesis kept in the gutter than we calculated with the numerical model. And, there is a delay of 10-20 seconds inthe experimental setup, because of the initial filling of the tubes. However, generally the models givesimilar outcomes and we may conclude that the numerical model can be used to study the functioning of theStorage Tank (http://www.youtube.com/watch?v=CY1_DboFpak).Numerical model result after infiltration (t=75 min)Numerical model result during recovery (t=1363 min)Experimental model result after infiltration (t=75 min)Experimental model result during recovery (t=1363 min)Sensitivities.Width and depth of the Storage Tank. A wider Storage Tank could serve a wider area above ground.However, the width of the Storage Tank is directly proportional to the volume of fresh water in the mixingzone at the bottom, and therefore a smaller Storage Tank is more attractive. Hence, the optimal width ishighly dependent on its final use. As for the influence of the depth of the Storage Tank on the recoveryefficiency; results show deeper walls will lead to higher recovery efficiency for all modeled circumstances.This is because the width of the mixing zone stays the same and therefore the amount of freshwater lost inthe mixing zone stays the same. Due to the larger capacity caused by the deeper walls; relatively the amountof fresh water lost gets smaller.Leakage. When a larger volume of fresh water is injected than the capacity of the Storage Tank, this willresult in leakage under the impermeable barrier. Therefore an optimal size of the Storage Tank exists. Dueto the density difference, the leaking fresh water will float up directly next to the impermeable barrier whereit spreads out. It seems to be impossible to recover this water via the Storage Tank and therefore, this wateris considered lost. However, the fresh water will presumably do no harm to the surrounding environment.Soil properties. In case of larger porosities; larger voids lead to a larger capacity of the Storage Tank. Therewill be less leakage under the impermeable wall and will lead to a higher recovery efficiency. On the otherhand larger conductivities lead to a faster leaking process. When the maximum capacity of the Storage Tankis reached, the recovery efficiency quickly degrades for higher conductivities.270

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCONCLUSIONSFresh water storage in saline aquifers seems feasible by means of the Storage Tank. The main characteristicof the Storage Tank is by using vertical subsurface impermeable barriers in a shallow saline aquifer thefresh water in stock is horizontally locked on top of the saline water below functioning as the tank’s variablebottom. The stored and recoverable volume of fresh water depends on the width and depth of the StorageTank, and on the characteristics of the aquifer. Our modeling results show that the recovery efficiencyincreases from 30% in the first cycle to more than 70% in the fifth cycle in the lab-scale configuration.Further research will include investigation of the effect of evaporation and well extraction and modelingwith real-case aquifer characteristics.LITERATUREGinkel, M. van, Olsthoorn, T.N., Smidt, E., Darwish, R., Rashwan, S., 2010. Fresh Storage SalineExtraction (FSSE) wells, feasibility of fresh water storage in saline aquifer with a focus on the Red Seacoast, Egypt. ISMAR7 proceedings.Guo, W., Langevin, C.D., 2002. User’s Guide to SEAWAT: a computer program for simulation of threedimensionalvariable density groundwater-flow. USFS Open file report 01-434.Kumar, A., Kimbler, O.K., 1970. Effect of Dispersion, Gravitational Segregation, and FormationStratification on the Recovery of Freshwater Stored in Saline Aquifers. Water Resources Research, Vol. 6,No. 6, p 1689-1700.Merrit, M.L., 1986. Recovering Fresh Water Stored in Saline Limestone Aquifers. Groundwater Vol. 24,No. 4, p 516-529.Olsthoorn, T.N., 2011. User Guide for MfLab. Mflab.googlecode.com.Pyne, R.D.G.,1995. Groundwater Recharge and Wells: A guide to Aquifer Storage Recovery. LewisPublishers, Boca Raton, Florida, USA.Full paper available on: http://blackboard.tudelft.nl/bbcswebdav/users/bdestombe/ASR_Storage_Tank.pdf271

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesLOCAL CLIMATE PROOF FRESH GROUND WATER SUPPLY: AN ADAPTIVE WATERMANAGEMENT STRATEGY WITH REGIONAL IMPACTGHP Oude Essink, ES van Baaren, PGB de Louw, J Delsman, M Faneca, P PauwDeltares, Subsurface and Groundwater Systems, PO Box 85467, 3508 AL Utrecht, The Netherlands,Phone: +31(0)88335 7139, Email: gualbert.oudeessink@deltares.nlAbstract: The Water System in the Netherlands is at risk. Climate change, sea level rise, landsubsidence and anthropogenic stresses will very likely make the present service level of fresh wateravailability impossible. This is especially pressing under dry (summer) conditions. For this reason,the theme fresh water supply is a top priority in the Delta Programme and the National Water Plan.National adaptive strategies are being developed now. In this paper, we will discuss one adaptivestrategy: Climate Proof Fresh Ground Water Supply for the Southwestern Delta, a low-lying salineenvironment in The Netherlands. Two showcases are set up: a. Infiltration via drainage, storage andrecovery of freshwater in a sandy creek ridge, and b. Optimizing the freshwater volume in shallowrainwater lenses by different types of deep drains. Farmers, knowledge institutes and localgovernments work together to make it a success. By combining monitoring campaigns (datacollectionand geophysical methods) and numerical modelling of variable-density groundwater flowand coupled solute transport, the efficiency of these measures will be evaluated, and if worthwhile,implemented in other regions.Keywords: fresh water supply, salinisation, groundwater, climate change, water management,climate change1. INTRODUCTIONWater management in the Dutch coastal zone is at risk. Salt water wedges intrude river and estuarinebranches, leading to external salinisation of the surface water system (fig. 1a). At the same time,internal salinisation of the groundwater system is continuously taking place; this process was initiatedsome centuries ago when we started to drain our land (fig. 1b). Both types of salinisation processesthreaten agriculture, drinking water supply and nature. On top, the following future physical driverswill jeopardize our water system even more (fig. 2): climate change (including sea level rise), land subsidence (up to 1 m per century in the peat areas), necessary operational water management strategies (e.g. adapting water level).For instance, modelling results of salt water intrusion in The Netherlands show that the water systemsignificantly becomes more saline these coming 100 years (fig. 3). Water courses need to be flushedmore intensively if water boards want to maintain the present water quality in the surface watersystem (Oude Essink et al., 2010; Oude Essink, 2011).To make The Netherlands Climate Proof for the coming century, fresh water supply is (next to safetyagainst flooding) one of the top priorities in the Delta Programme and the Dutch National Water Plan.National adaptive strategies are being developed to make this happen, supported by researchprograms.272

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 1: a. External salinisation of the surface water system b. Development of the Dutch polder region (Wesseling, 1980).A. Before occupation of man; B. After damming of the streams at their mouths and their embankment, separation of'boezem' and 'polder' by small dikes; C. Subsidence of the peaty polder soils and pumping of windmills; D. Digging out ofsome polders for peat making; E. After draining of the lake originating from peat making; F. Present situation.273

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives2. CLIMATE PROOF FRESH WATER SUPPLYClimate Proof Fresh Water Supply is such a research program. One of the aims of this Knowledge forClimate project is to develop robust, flexible and long-term solutions that can contribute to successfulwater management strategies in our changing Dutch Delta (fig. 4). Several knowledge institutes(Deltares, Alterra, KWR, Acacia, TNO) and universities (PhD’s at VU, WUR, TUD, UT) areresearching the effects of Climate Change on ecology, hydrology and hydrogeology (such as saltdamage to crops, volumes of freshwater lenses, etc.). In addition, the robustness and flexibility of thewater system in response to climate change is analyzed, and policy tipping points 1 in present watermanagement are identified.Fig. 2: a. Schematization of the groundwater system in the Dutch deltaic area; b. Possible processes that occur in case ofclimate and global change.Main questions of this project are:how will the spatiotemporal patterns in the fresh water availability in ground- and surface waterin coastal lowland regions change due to climate change;how can effective regional adaptation strategies be implemented to sustain present waterdependentfunctions in the future?what is the potential of measures to either increase water availability or decrease water demand?to what extent do these strategies contribute to a national solution for a climate proof freshwatersupply?We will investigate whether or not a combination of local to sub-regional adaptive strategies (workedout in showcases) exists to make regional fresh water supply possible in the future.1 A policy tipping point is a point where the magnitude of chance is such that the currentmagnitude strategy can no longer meets its objective. Themes are coastal defence, salinisation,nature, accessibility harbour Rotterdam.274

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 3: Salinisation and freshening at the top ofthe groundwater system in 2100 AD relative to 2010 AD due to autonomous development (caused by past lowering inpolder water levels). Modelling results from Netherlands Hydrological Instrument (NHI fresh-salt).Fig. 4: Scheme with work packages and activities of the Knowledge for Climate project Climate Proof Fresh Water Supply.3. METHODOLOGY275

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesThe following (straightforward) steps towards a setting with a robust fresh water supply can beidentified:(a) better understand the present water system,(b) assess the impact of future climate and anthropogenic stresses to (ground)water,(c) communicate and cooperate with (local) stakeholders, like farmers and water board,(d) come up with and implement feasible, robust and flexible strategies for future water management:start with showcases and upscale to larger regions.In this article, we focus on the local groundwater system, viz. the shallow freshwater lens (fig. 5) andthe medium scale freshwater lens in sandy creeks. We strongly believe that the third (vertical)dimension of this groundwater system can make a difference: storing the surplus of fresh water in thesubsoil in the wet winter period and use this water during dry summer periods is promising.Numerical models of the fresh-salt groundwater system on local to sub-regional scale are constructedand monitoring campaigns are executed to show the efficiency and thus to increase the success of thestrategies. Stakeholder participation processes (inform, communicate with and learn fromlocal/regional policy makers, farmers, drainage companies) will also increase the implementation ofpossible successful solutions in the field.The location of the showcases is in our Southwestern Delta, a low-lying saline environment in theNetherlands with high climate proof fresh groundwater supply potentials and where stakeholdersstrongly support innovations in water issues.4. BETTER UNDERSTAND THE PRESENT WATER SYSTEM: THE FRESHWATER LENSDuring the past years, extensive research has been executed, from fieldwork for the collection ofgeophysical, hydrological and geohydrological data to better understand the behaviour of freshwaterlenses. In addition, numerical modelling is executed to predict the impact of sea level rise, climatechange and measurements to adapt to and mitigate the salinisation (Oude Essink et al., 2009; DeLouw et al.,2011; Eeman et al,, 2011).In many Dutch low-lying areas, saline groundwater is often encountered at shallow depths (< 10-15m). Precipitation surplus lead to the forming of rainwater lenses on top of saline groundwater. Thethickness throughout the seasons may have major implications for these freshwater lenses. On top ofthe climate effects of rainwater lenses depends on factors like recharge, seepage flux, salinity,drainage characteristics. They vary in thickness from > 50 m in dune areas, 5 to 20 m in fossil sandycreeks to < 1 to 2 m in agricultural parcels in polder areas with prominent saline. The fresh wateravailability for agricultural purposes depends on these shallow and medium freshwater lenses.276

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 5: a. Conceptual visualisation of a shallow freshwater lens on top of saline groundwater seepage; b. Map ofvulnerability of shallow freshwater lenses on salt damage to crops.5. ASSESS IMPACT OF FUTURE CLIMATEThe next step is to answer whether or not this vulnerable shallow fresh groundwater system issensitive to climate change, sea level rise, land subsidence and possible anthropogenic pressure (suchas intensive groundwater extraction) (see also fig. 5b). Changes in precipitation and evaporation bothin quantity and seasonal distribution as well as sea level rise will accelerate saline seepage in thelower lying areas. Moreover, the freshwater lenses will especially be vulnerable during summer time,when both precipitation deficits and groundwater extractions for agricultural purposes are the largest.Fig. 6 shows an example of the effect on fresh groundwater volumes in a freshwater lens under theso-called W+ climate change scenario: the shallow freshwater lens will disappear and the creek ridgefreshwater lens will be minimized. However, it is still unclear how these fresh water lenses in thewhole region exactly react under new climate, sea level and socio-economical conditions, and howwater management in these low-lying areas will anticipate.277

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 6: Vulnerability of a freshwater lens to climate change and sea level rise (under W+ climate scenario): green meansthat concentration in top water system is so high that salt damage to crops is likely to occur. Upconing saline groundwaterfrom deeper parts of the system towards the surface water ditches can clearly be seen.6. COMMUNICATE AND COOPERATE WITH (LOCAL) STAKEHOLDERSPretty straightforward, but communication and cooperation with local stakeholders will make adifference! Site-specific knowledge such as on drainage and ditch characteristics, soil conditions andcrop production in the field can make a measure successful. When correctly instructed, they can evenhelp in data collection during monitoring campaigns.Fig. 7: Communication with stakeholders: their local knowledge and eagerness to adapt to a changing environment isessential to make measures for climate proof fresh water supply, suggested by hydrogeologists (photos by courtesy of VanBaaren, Rentmeester and Van der Hoek).278

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectives7. COME UP WITH FEASIBLE, ROBUST AND FLEXIBLE STRATEGIESWe will work out three showcases (fig. 8) this coming year, of which two are worked out here:1. Infiltration via drainage, storage and recovery of freshwater in sandy creek ridges in a salineenvironment (ASR), utilizing the potential of the creek ridge for water storage, with the focus oninfiltration of surface water via drains.2. Optimizing the freshwater volume in shallow rainwater lenses by different types of (deep)drains.Fig. 8: Local (ground)water solutions to make Local Climate Proof Fresh Groundwater Supply possible.This coming year, we will use monitoring campaigns and modelling exercises to show the efficiencyof these measures.8. INTERNATIONAL POSSIBILITIESThe fresh water shortages problems we are detecting in the Netherlands are basically worldwideproblems. It is evident that with changing climate and global conditions, the stresses in the coastalzone are intensified. Fig. 9 show some possible regions with future problems. Various watermanagement strategies should be developed to cope with different circumstances.279

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesFig. 9: Shortage of fresh groundwater resources is a world-wide problem: some examples.9. CONCLUSIONSIn the Southwestern Delta, a low-lying saline environment in The Netherlands, there is a momentumto implement adaptive strategies based on Local Climate Proof Fresh Groundwater Supply (fig. 10).The base idea is to store the surplus of fresh water in the subsoil in the wet winter period and to usethis water during dry summer periods is promising. By increasing the freshwater volume in thesubsoil, more fresh water is stored for times of water deficit.Farmers, knowledge institutes and local governments work together to make the showcases a success.By combining monitoring campaigns (data-collection and geophysical methods) and numericalmodelling of variable-density groundwater flow and coupled solute transport, the efficiency of thesemeasures can be evaluated.Fig. 10: A combination of local(ground)water solutions to make Local Climate Proof Fresh Groundwater Supply possible.280

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesREFERENCESEeman, S., Leijnse, A., Raats, P.A.C. and van der Zee, S.E.A.T.M., 2011, Analysis of the thickness ofa fresh water lens and of the transition zone between this lens and upwelling saline water, Advancesin Water Resources 34 (2011) 291–302.Goes, B.J.M., Oude Essink, G.H.P., Vernes, R.W. and Sergi, F. 2009. Estimating the depth of freshand brackish groundwater in a predominantly saline region using geophysical and hydrologicalmethods, Zeeland, the Netherlands, Near Surface Geophysics 401-412.Louw, P.G.B., de, Eeman, S., Siemon, B., Voortman, B.R., Gunnink, J., Baaren, E.S., van and G.H.P.Oude Essink, Shallow rainwater lenses in deltaic areas with saline seepage, Hydrol. Earth Syst. Sci.Discuss., 8, 7657-7707, 2011.Oude Essink, G.H.P., Louw, de, P.G.B., Stevens, S., de Veen, B., de, Prevo, C., Marconi, V. en Goes,B.J.M. 2009, Monitoring campaign in the occurrence of freshwater lenses in the Province of Zeeland,2007-U-R0925/A, 132p.Oude Essink, G.H.P., E.S. van Baaren, and P.G.B. de Louw, 2010, Effects of climate change oncoastal groundwater systems: A modeling study in the Netherlands, Water Resour. Res., 46, W00F04,doi:10.1029/2009WR008719.Oude Essink, G.H.P., 2011, Salinisation of groundwater resources in the Dutch Deltaic area:modelling, monitoring, climate change and solutions, Homage to Emilio CustodioWesseling, J. 1980. Saline seepage in the Netherlands, occurrence and magnitude. Research onpossible changes in the distribution of saline seepage in the Netherlands, Committee for hydrologicalresearch TNO, Proc. and Inform. No. 26.: 17-33.281

22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSEA WATER IN THE TELDE VOLCANIC AQUIFER,GRAN CANARIA ISLAND (SPAIN)Cabrera, M.C. (*) and Custodio, E. (**)(*) Department of Physics, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria,Spain. mcabrera@dfis.ulpgc.es(**)Department of Civil Engineering and Center for Groundwater Hydrology , Technical Universityof Catalonia, Spain. emilio.custodio@upc.eduAbstract: The coastal aquifer of Telde is located in the eastern part of Gran Canaria volcanic Island,Spain. The 75 km 2 area consists in modern (Quaternary) basalts and the Miocene phonoliticFormation, which are separated by volcanoclastic and volcano-sedimentary deposits of Las PalmasDetritic Formation that includes silts, sands, heterogeneous gravels and piroclastic and lava flows ofthe explosive Roque Nublo breccias. The area was intensively developed since the late 19 th centuryfor irrigated agriculture, peaking in the 1950s and 1960s, using local and imported inlandgroundwater. About 150 large-diameter excavated wells exist in the area, most them penetratingdown to below sea level. Many of them have been progressively deepened until the 1990s. Currentlya large part of the area is transformed into urban, industrial and services establishments, withdecreased agricultural activity. In spite of part of the wells becoming idle, more than 20 wells supplybrackish to saline water to more than 15 local desalination plants. Groundwater behavior andcharacteristics is complex, as the aquifer is. Many wells have been affected by salinization in thecoastal fringe from lateral intrusion (Cl contents up to 2500 mg/L) or by saline water upconing(reaching 8000 mg/L Cl in some points). Seawater intrusion is characterized by ion exchange thatproduces hardened mixed waters in some wells, but other wells present different conditionsdepending on their situation, depth and exploitation regime. The analysis of the aquifer functioningand the temporal evolution of the groundwater geochemistry is considered in order to differentiateseawater intrusion from return irrigation flows when the applied water is of poor quality. The recentoperation of wells to supply the desalination reverse osmosis plants is increasing the salinity ofnearby wells. This aquifer is a complex system that needs control and improved governance throughespecially dessigned institutions.282

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