Groundwater Surface Water Interaction. Methods and Case Studies

Transcription

1 Groundwater Surface Water Interaction Methods and Case Studies Stephan M. Weise UFZ-Department of Isotope Hydrology

2 Groundwater Surface Water Interaction is a process relevant for... Salinisation of fresh groundwater due to sea water intrusion Intrusion of contaminated groundwaters into surface water Developement of pit lakes highly contaminated and acidified by lignite mining Groundwater un-covered by gravel production

3 1. Sea water intrusion Problem: Over-exploitation of costal-near groundwater reservoirs causes intrusion of sea water Measures: Accurate ascertainment of the groundwater reservoir to avoid over-exploitation Tools: - Monitoring of hydrochemical evolution - Definition of size of reservoir with environmental isotopes

4 1. Sea water intrusion areas of investigation

5 1 Tools Stable isotopes ( 2 H, 18 O) of water Information about the origin of water Tritium ( 3 H) of water and 3 He of dissolved gases Information about the residence time of water Noble gas temperature Distinction between sea and juvenile waters study in progress

6 2 Contaminated groundwater Problem: Groundwater highly contaminated with heavy metals infiltrates into surface water (inverse to river bank filtration) Measures: Under discussion yet, but at first Determination of the flow system as basis of further steps Tools: Hydrochemical monitoring Detection of inflow by temperature

7 Study Site km C.Schmidt et al C. Schmidt et al. (2006):Characterization of spatial heterogeneity of groundwater-stream water interactions using multiple depth streambed temperature measurements at the reach Scale. Hydrol. Earth Syst. Sci. Discuss., 3,

8 Concept High Groundwater Discharge Medium Groundwater Discharge Low Groundwater Discharge Vertical Flow can be obtained from a simple one-dimensional analytical solution of the heat diffusion advection equation

9 Measurements Assumption: Observed streambed temperatures represent spatial differences of groundwater discharge Streambed temperatures are measured by temporarely inserting a probe into streambed Temperature in C

10 Results Flow direction Stream 0.1m depth Distance 220m 0.5m Temperature in C Streambed Zones of high groundwater discharge

11 Results Temperature profil can be converted to a water-influx profil

12 3 Mining lakes Problem: Flooding of holes from lignite mining activity are acidified (down to ph = 2) and contaminated with heavy metals Measures: Development of remediation strategies dependent on groundwater-lake water interaction Tools: - Inflow/outflow balance with environmental isotopes - Detection of inflow by 222 Rn and stable isotopes - Governing biogeochemical cycles at benthos

13 Lignite mine district Koyne-Plessa RL-117 RL-111 RL-7

14 Mining Lake RL 111

15 3 Test site RL 111 Quartär angeschnittene Tertiärsedimente Förderbrückenkippe Quartärhalde Kippenböschung Grundwasserfließrichtung cross section Messstelle S Quelle Probenahmeort See A1 S-Q A2 A3 ML 111 A4 D3 D2 A5 D6 D5 D4 Germany Leipzig N Messstelle Length 900 m Width 180 m Depth m Area m 2 Restloch 111 S-D D m GWL Mixolimnion Kippe Braunkohle Grundgebirge Monimolimnion

16 3 Determination of fluxes high-resolution concentration profiles Millimeter scale micro sensors O 2 c x concentration (R. Stellmacher 2006)

17 RL 111: micro senors sediment-water interface Exfiltration FM_NB m depth Konzentration [mmol/l] Position [mm] Konzentration [mmol/l] GW-neutral FM_NB2 7.0m depth Konzentration [mmol/l] Position [mm] Infiltration FM_SB1 1.5m depth Groundwater flow direction Position [mm] (R. Stellmacher 2006) Position of sensors 70

18 3 Determination of fluxes provides information about fluxes and biogeochemical processes In situ sediment incubation Benthic Chamber Change of concentration with time matter flux direct flux determination with simulated flow

19 3 Determination of fluxes high-resolution concentration profiles Decimeter scale DET (Gel Peeper) Dialysis pore water sampler (DPS) front view side view diffusive equilibrium (R. Stellmacher 2006)

20 RL 111: DP sampler high inflow little inflow stagnant distance from sed./water interface (cm) nothing is perfect! S-Südbecken 0.5m S-Südbecken 2.5m -,0-8,0-6,0-4,0-2,0 0,0 δ 18 O-H 2 O ( VSMOW) distance from sed./water interface (cm) W-Südbecken 0.5m W-Südbecken 2.5m Monimolimnion -60 -,0-8,0-6,0-4,0-2,0 0,0 δ 18 O-H 2 O ( VSMOW) Groundwater flow direction Position of DPS (K. Knöller and S. Weise 2006)

21 Using 222 Rn to detect groundwater inflow into a lake Radon is a naturally occurring radioactive gas, with a non-reactive nature and a short half-life life (t 1/2 = 3.83 d) Diffusion cell for on-site Rn analytik Radon concentrations of groundwater are very large enriched to surface water (often 00-fold or more) Radon is an excellent tracer to identify and quantify significant groundwater discharge. Flux atm Inventory [Bq m - ²] (atmosphere) (lake) The approach for quantifying gw discharge is a steady-state state system with a consideration of all 222 Rn sources and sinks related to the lake. gw-discharge [cm d -1 ] (Axel Schmidt, UFZ, Dept. Analytical Chemistry) Total Radonflux [Bq/m² d] diffusion, other processes (groundwater)

22 Using 222 Rn to detect groundwater inflow into a lake Example: Tagebaurestloch RL 7, Plessa area: 125,000 m², m, medium depth: ~3 m ph = 2.4; Fe = mg/l; SO 2-4 = g/l Data: Flux atm = 2 ± 0.16 [Bq[ m -3 ] Inventory = 75 ± 1.8 [Bq m -² ] Diffusion = 0.2 [Bq m -3 ] Radonflux = 414 ± 9.9 [Bq/m² d] Groundwater discharge: ± cm d -1 Radon is a excellent tracer to quantify groundwater discharge gw-discharge [cm d -1 ] Flux atm Inventory [Bq m - ²] Total Radonflux [Bq/m² d] (atmosphere) (lake) diffusion, other processes (groundwater) (Axel Schmidt, UFZ, Dept. Analytical Chemistry)

23 RL 111: Isotopic balance Basic input: - annual variation in isotopic composition of lake water - isotopic composition and amout of precipitation - isotopic composition of groundwater - surface in- and output - (estimates of) evaporation annual groundwater inflow: 23700m 3 annual groundwater outflow: 15700m 3 (K. Knöller 2001)

24 SO 4 2- Cl - Fe ges Al 3+ ph 4.20 P ph 4.19 P ph 3.55 BZL Ca 2+ Mg 2+ K + [mg/l] ph 3.05 BZL111-2 RL 111: Ground- and dump water (isotope-) geochemistry 000 ph RL111-0m ph 5.17 P ph 5.01 P ph 4.08 P ph 2.57 NE-SEE SO4 vary between 40 and 700 mg/l in the aquifers ground- and lake water SO4 reaches chemistry 4300 mg/l at max. in dump of the water ML111 area ph 4.18 P δ 34 S: 9.9 to +23 %o in GW δ 34 S: +7 and +32%o in dump water sampling point lake water mg/l -9, ,0 N 0 +3,8 320 N inflow dump +7, , , N +8, inflow aquifer δ 34 S CDT SO (mg/l) 4 δ 34 S CDT SO 4 (mg/l) +6,0 50 N +23,1 N 40 +5, ,5 390 outflow of lake water into aquifer +32,0 320 N Mining Lake 111 sampling wells aquifer sampling wells dump

25 RL 111: Results of isotope geochemical investigations Sulfat from mining dumps is reduced in the aquifer west of RL 111. In the dump, oxidation of pyrite and mobilisation still provides a permanent sulphate input into the lake. Consequently, for remediation measures the groundwater inflow from dumps have to be taken into account

26 Mining lakes: Perspective from mining landscape to recreation landscape Cospudenminingarea (south of Leipzig)

27 4 Gravel production dis-covers high-productive aquifers and connects a groundwater flow system with lake water. Issues: What is the intensity of groundwater-lake connection? What is the effect on groundwater quality?

28 4 Case study Lake Leis Germany Study area groundwater table [asl] Hori Well investigated 3 for H content V20 V Lake Leis Lake Leis: Surface area: 116,000 m 2 Depth: 21 m (in average) annual turnover V7 V6 Aquifer: DP9 DP11 DP Groundwater flow direction Geology: Quaternary gravel and sands Groundwater flow velocity: m/d (S. Weise, W. Stichler, B. Bertleff 2001)

29 4 Lake Leis: Tritium age 00 Tritium content [TU] H range of deeper groundand Lake Leis waters Apparent age Yearsbeforedateofsampling 3 H in precipitation corrected for decay

30 Depth [m] 4 Lake Leis: 3 He/ 3 H age Circulation zone Stagnation zone Range of apparent 3 H ages Lake Leis apparent 3 He/ 3 Hage [years] exchange with atmosphere (degassing) resets 3 He/ 3 H age close to zero age of about 20 years though the lake turns over every year

31 4 Case study Lake Leis Results from 3 He/ 3 H investigations: groundwater inflow is about 2000 m 3 /d. regarding known hydraulic conductivities, the area effective for inflow is between 500 and 7500 m 2, consistent with lake's crosssection area of about 6000 m 2. Lake Leis must be extremely good incorporated into the regional ground water flow regime.

32 Mining lakes Merseburg Ost