Involved institutions and persons LIAG: Franz Binot, Dieter Epping, Thomas Grelle, Michael Grinat, Phil Hesse, Raphael Holland, Jan Igel, Paul

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1 Involved institutions and persons Pilot area D: Borkum LIAG: Franz Binot, Dieter Epping, Thomas Grelle, Michael Grinat, Phil Hesse, Raphael Holland, Jan Igel, Paul Königer, Robert Meyer, Sonja Möhring, Susanne Stadler, Hans Sulzbacher, Detlef Vogel, Helga Wiederhold, Thomas Wonik, Regine Ziekur BGR: Uwe Meyer, Bernhard Siemon, Annika Steuer LBEG: Jörg Elbracht, Gabriele Ertl, Andree Weustink HSW: Sebastian Winter (engineering office) Wirtschaftsbetriebe Borkum (waterworks) Hölscher Wasserbau GmbH (drilling company) Region Midtjylland: d Henrik R. Larsen, NN GEUS: Klaus Hinsby, Per Jensen, NN Vitens and Deltares (Arjen Kok, Jan Gunnink)

2 Borkum Frisian Island 10 km E W 7 km N S 31 km 2 largest of East Frisian Islands Elevation max 24 m asl in dune ridges, less than 4 m elsewhere exposed position in estuary of river Ems North Sea health resort (2004: 280,000 visitors, 5437 inhabitants)

3 Borkum Freshwater lense only fed by precipitation and infiltration h z ρ F ρ S hydrostatic conditions Ghijben & Herzberg: ρsaltwater g z = ρfreshwater g ( z + h) ρ SALTWATER z = 40 h g / cm 3 h = height of freshwater table above sea level z = depth below sealevel to saline water interface ρ F, ρ S = freshwater and seawater densities Freshwater aquifer is endangered by infiltration of saline water (storm tides, rising sea level)

4 Borkum Drinking water abstraction since 1965 Two distinct water catchment areas: Waterdelle (1.3 km 2 ) and Ostland (2.1 km 2 ) Waterdelle: Since 1900 waterwork I since 1949 wells 1-20 since 1956 wells Ostland: since 1970 wells (shallow) since 1972 wells (deep) 29 wells in four groups, filter 5-10 m below surface filterlength 4-8 m in m below surface FUK m below surface The actual (2008) riparian right allows annual extraction of max12miom 1.2 mio m 3 (04miom (0.4 m 3 in Waterdelle and 0.9 mio m 3 in Ostland) 89 groundwater observation wells (29 in Waterdelle, 60 in Ostland) 59 of these are read monthly (22 in Waterdelle, 37 in Ostland), others twice per year FUK = Filterunterkante

5 Borkum Architecture of the aquifer: Upper and lower ground-water storeys Divided by 1-2 m thick boulder clay (Geschiebelehm) in about -20 m msl Hydraulic seperation of both only local FUK = Filterunterkante

6 Geological sections 10 NN Borkum -20 m Aus: Streif, 1990, Geologischer Führer, 57 Barrier island N Geological scheme of coastal deposits for the last 8500 years: S Aus: Berner & Streif, 2000, Klimafakten continuous sea level rise forming of holocene sediment wedge

7 Modell Scale and vertical resolution:? Base horizon:? Data base and modelling Data base for 2D/3D modelling Boreholes 2 Hydrogeological cross sections 40 CPT s (EC log, groundwater probing EC and chlorid) GPR (xx km 200 MHz, xx km 80 MHz, CO and CMP) VES (classical Schlumberger arrays from 1992 and 2008 (36 soundings)) CVES (2D, 3 profiles) HEM data (area: 75 km 2, 550 km profile length, 35 NW-SE (250 m), 11 SW-NE (500 m)) 2 deep wells CLIWAT_1 (67,5 m) & CLIWAT_2 (77 m) with vertical electrode chains for monitoring fresh-/salt-water transition zone Pumping tests ( kf values) Groundwater probing (chemistry and isotopes). EC=electrical conductivity) CO = constant offset CMP=common midpoin HEM = helicopter-borne electromagnetic method, frequency domain

8 Boreholes and hydrogeological cross sections

9 Geological/hydrogeological section (S-N) SSE NNW SE NW ESE WNW SSW NNE SE NW 10 NN m Gabriele Ertl

10 Geological/hydrogeological section (W-E) WSW ENE Westland Waterdelle Ostland 10 NN m -70 Gabriele Ertl

11 Geological/hydrogeological classification Stratigrafie Lithologische Lithologische/ lithogenetische Einheit Kürzel Hydro- GIS Kombi-Nr. Durchlässig Ausprägung stratigrafische keitsklasse (überwiegend) Einheit Holozän Sand-Schluff, Künstliche Auffüllung qh(y)//y L0 18 Bauschutt? Holozän Überwiegend Watt, Strand qh/fs-ms/wa,st L1 Bitte neu Feinsand (teils vergeben tonig, schluffig) Pleistozän Weichsel Sand Rinnenbildung qh/s/rn L1 Fein-Mittelsand Dünenbildung qh/fs-ms/d L Torf, Schluff, Ton, Aufspaltungssequenz, Organische qh/h,t,u,sl,uk/br-,,, H1 Klei, Schlick Basalsequenz; Moor, Marsch, Brackwatt, m,h Schlickwatt Sand (überwiegend Feinsand) fluviatil, Dünenbildung qw/fs/f,d L1 Weichsel Kies, tonig fluviatil qw/g/t/f L1.3 Eem Ton, Schluff Beckenablagerung qee?,qw?/t,u/b H Eem Sand (teils tonig, schluffig) marin, fluviatil qee/fs/m,f L1.4 Bitte neu vergeben Saale Geschiebelehm/- h Drenthe-Grundmoräne, qd//lg,mg H (Drenthe) mergel Schluff, Ton Drenthe-Beckenablagerungen qd/t,u/b H Sand, Kies glazifluviatil qd//gf L Lauenburger Ton, sandig ql/t,u/b H Ton Pliozän Sand (teils feinkiesig) ungegliedert tpl/s/ L Legende für Schnitte SSE-NNW Borkum und W-E Borkum Stand: Tbll Tabelle 1 aus Geofakten fkt Nr. 21

12 Boreholes

13 Boreholes Boreholes B h l Wells Schlumberger VES CVES Direct push

14 HEM 1D-inversion: resistivity maps and vertical sections Bernhard Siemon / Annika Steuer

15 Specification of HEM-inversion using the example Waterdelle comparison of HEM, direct push, VES and drilling profile L16.11 Bohrung 12 Bohrung 2 WWBO 1026 BORK II m Ton m Torf 9.5 m ab 8.9 m Ton 18 m NW DP 06 GTS 8 HEM L16.1 WWBO 1026 BORK II 811 SE DirectPush HEM 78 GTS 8 (VES) 9890 Ωm Ωm 20 data fit H_F5_10_S3_L6_D2_SF100_200 H_F5_10_S3_L4_D2_SF100_200. GOK [m] Tiefe u m Annika Steuer / Bernhard Siemon m

16 2D/3D geological model GOCAD HEM data ready for input (xyz data) end of November 2009! interpretation of layers manually

17 mapping of saline groundwater by resistivity methods What is saltwater? Chloride concentration exceeding 250 mg/l (can be tasted) Electrical conductivity exceeding 2500 μs/cm = 250 ms/m = 4 Ωm (EU-directive on water quality) or Goes et al (Near Surface Geophysics ): Fresh-brackish groundwater interface 150 mg/l 6 Ωm Brackish-saline groundwater interface 1000 mg/l 1 Ωm

18 mapping of saline groundwater by resistivity methods clay-free material Archies law ρ = F ρ aquifer water m F = a φ F = formation factor F a, m constants a reflects influence of min- eral grains on current flow, = 1 for perfect insulator m reflects porosity exponent, cementation degree, if we know F, we can calculate ρ water from ρ water the total salinity can be estimated e.g. (chlorid concentration?) Loose sands: a=1, m= 1.3 Sandstones: a=0.7, m= 1.9

19 mapping of saline groundwater by resistivity methods clay-free material Archies law ρ = F ρ aquifer water F m = a φ F = formation factor F if we know F, we can calculate ρ water from ρ water the total salinity can be estimated (chlorid concentration?) e.g., Goes et al. (Near Surface Geophysics, 2009: : 1) Estimate groundwater resistivity via soil resistivity and F 2) Temperature correction of groundwater resistivity 3) estimate chlorid concentration

20 Formation factor versus grain size ρ m sediment = a φ ρ porewater From: TNO 1976 (in Kirsch (ed.) 2009)

21 Pore water resistivity versus chloride content ρ m sediment = a φ ρ porewater From: TNO 1976 (in Kirsch (ed.) 2009) Empirical relation between chloride concentration and electrical resistivity it of groundwater at 20 C for various bicarbonate concentrations (from Goes et al. 2009)

22 mapping of saline groundwater by resistivity methods We need this for the variable density groundwater model Can we rely on the resistivities?? What corrections do we need?????