Friday, 15th December 2006
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
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.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 originTYPOLOGY 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 classificationPrimary 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
TYPOLOGY: Primary parameters
Grouped Ten basic units Detailed
Carbonates Limestone (Karstic/non karstic)
Karstic carbon. rocks, Paleozoic Carbon rock, carbon rocks and interbedded silicatic carb. Rock,…
group Chalk
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 Crystalline basement
group Schists
Volcanic rocks Evaporites
Saline influence
Map based on typology: - application to the first aquifer
compartment
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
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 (3H, 3H/3He, CFC, SF6, δD, δ18O) may be helpful
Gap: Transfer time (+ Stocks of pollutants) in the vadoze zone less known than in the groundwater
Interactions between groundwater and its associated surface waters and terrestrial ecosystems
The baseflow : a key parameter in potential dilution of pollutants
Baseflow estimation methods
Tier 1
Tier 2
Tier 3
•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
Increasingeffort, cost, complexity andreliabilityofresults
Gap: simple modelling tools for considering the links between GWB and SW / GWDTE
Attenuation- Main parameters
Driving Parameters Solid/aqueous phase
Attenuation processes
Carbonates Oxides, clays Organicmatter Sulfidesmin. pH Salinity
Precipitation x x x x x
Sorption x x x x
Cations exchange x x x
Volatilization x
Biotic/abiotic degradation x x x
Aquifer’s capabilities of attenuation
Carbonates Oxides, clays Organicmatter Sulfidesminerals
pH
Limestone
(Karstic/non karstic) Chalk
Sands and gravels Marls and clays Sandstones
Crystalline basement Schists
Volcanic rocks x x variabl
e
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
Taking attenuation into account for threshold determination
Monitoring point for TV determination
Attenuation along flowpath
Receptor
M R
- If attenuation occurs downstream of monitoring point, it allow determination of less restrictive TV- but:
- Longevity and sustainability of attenuation must be verified 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 Receptor
Attenuation along flowpath
M R
Possible controversy on pollutant origin
Do not confuse geogenic and natural ( NBL) origin;
>
Denitrification is very common within European Aquifers•
NO3 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•
NTDS induces N 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….Concluding Remarks
Understanding the chemical composition of groundwater (origin, fate and transport of substances) is a key challenge in TV
derivation.
