Hydro-geological and geochemical characterisation for determination of thresholds values in groundwater - Typology of aquifers

Transcription

1 Hydro-geological and geochemical characterisation for determination of thresholds values in groundwater - Typology of aquifers Hélène Pauwels, Jan Hookey, Wolfram Kloppmann, Ralf Kunkel Synthesis of contributions to WP2 from BRGM, BME, EA, Fz-Jülich, LAGH-UGENT, IGME, ULG, HLUG, Uni-Aveiro, EAA, UT, TNO, GEUS, UBA-D, NAGREF, ABTEVERE, DHWP/AGH Bridge: final meeting Friday, 15th December 2006

2 Establishment of threshold value : Groundwater characteristics > Context : TV should be established for GW shown to be at risk and also for SW and GWTDE at risk and fed by groundwater; by taking account of behaviour of pollutants (origin, dispersion tendency, persistency potential). > Objective To highlight common features of European aquifers- relevant to the fate and transport of pollutants: To provide basic knowledge for the methodology; To provide recommendations for development of conceptual models of GWB.

3 Recommendations and Research Needs > Proposed typology > Response lag time of aquifers > Interaction between groundwater and its associated surface waters and terrestrial ecosystems > Attenuation > Possible controversy on pollutants origin

4 TYPOLOGY for hydro-geochemical characterisation of groundwater Justification of the typology : High hydro-geochemical heterogeneity within GWBs More common classification criteria applied for delineation of GWB Water abstraction classification Hydrogeological based classification Primary parameters that relate to the origin of compounds Lithology Saline influence Secondary parameters that related to processes Hydrodynamics Redox conditions Particular occurrences ( organic matter, oxides, sulphides minerals) Geological age

5 TYPOLOGY: Primary parameters Grouped Ten basic units Detailed Carbonates group Limestone (Karstic/non karstic) Chalk Karstic carbon. rocks, Paleozoic Carbon rock, carbon rocks and interbedded silicatic carb. Rock, Unconsolidated Sands and gravels Sands and clays, Glacial sand and gravel deposits, Fluviatil deposits,. group Marls and clays Sandstones Sandstones Trias. sandstones., sandstone /silicastic alternating sequences Hard-rock group Crystalline basement Schists Volcanic rocks Evaporites Saline influence

6 Map based on typology: - application to the first aquifer compartment

7 Residence time of GW Units 1 d 1 y 10 y 100 y 1000 y Limestone (Karstic/non karstic) Chalk Sands and gravels Marls and clays Sandstones Crystalline basement Schists Volcanic rocks Clear need of anticipation of any further spread of pollution

8 Taking response time lag into account for threshold derivation Recent GW must be involved within the process of TV derivation/ application. At monitoring level: Location of monitoring network must be representative of land use For characterization phase: -Appropriate characterisation of recharge conditions -Application of environmental tracers ( 3 H, 3 H/ 3 He, CFC, SF 6, δd, δ 18 O) may be helpful Gap: Transfer time (+ Stocks of pollutants) in the vadoze zone less known than in the groundwater

9 Interactions between groundwater and its associated surface waters and terrestrial ecosystems The baseflow : a key parameter in potential dilution of pollutants Tier 1 Tier 2 Tier 3 Baseflow estimation methods Little data Age/tracer//low flow survey Provides relative importance of groundwater input more data hydrograph separation with regional modelling gives better understanding of relative importance of groundwater input and spatial understanding within catchment large data requirement deterministic modelling gives predictive understanding of groundwater input under different conditions within catchement Increasing effort, cost, complexity and reliability of results Gap: simple modelling tools for considering the links between GWB and SW / GWDTE

10 Attenuation- Main parameters Driving Parameters Solid/aqueous phase Attenuation processes Carbonates Oxides, clays Sulfides min. Organic matter Precipitation x x x x x Sorption x x x x Cations exchange x x x ph Salinity Volatilization x Biotic/abiotic degradation x x x

11 Aquifer s capabilities of attenuation Carbonates Oxides, clays Organic matter Sulfides minerals ph Limestone (Karstic/non karstic) Chalk Sands and gravels Marls and clays Sandstones Crystalline basement Schists xx x x x basic xx x x x basic x xx xx x variab le x x x variabl e x x acid x x x acid Volcanic rocks x x variabl e

12 Taking attenuation into account for threshold determination Attenuation along flowpath Monitoring point for TV determination M M Attenuation along flowpath - If attenuation occurs downstream of monitoring point, it allow determination of less restrictive TV- but: - Longevity and sustainability of attenuation must be verified R Receptor Receptor Other gaps: - Local studies of attenuation within riparian / hyporheic zones have been carried out: difficulty lies in the scale up to the catchment sacle ; - Particular conditions of that may result in pollutant remobilization R

13 Possible controversy on pollutant origin Do not confuse geogenic and natural ( NBL) origin; > Denitrification is very common within European Aquifers NO 3 reactivity induces leaching of metals from sulphides minerals and adsorbed on Organic matter > Irrigation Salinisation induces leaching of some trace elements ( B, Se, Mo, As, F..) > GW withdrawal from coastal area TDS induces of [Ca] by cation-exchange and of metals by complexes formation > GW abstraction from confined/unconfined aquifer Mixing through leakage/drainage between aquifers, Mobilisation of some metals from sulphides minerals, Fe-hydroxides, Clay.

14 Concluding Remarks Understanding the chemical composition of groundwater (origin, fate and transport of substances) is a key challenge in TV derivation. > Proposed aquifer typology provides a general framework for such an understanding, but must be completed by information on transfer time; > Heterogeneity of GWB : a key point as GWD provides for appropriate investigation if TV is exceeded at one or more monitoring point ; > Scientific gaps have been identified but GWD provides for TV amendment if appropriate.