Overview of Groundwater Pollution Risk Assessment

1. EC-DGE (WG 2C) WORKSHOP < GROUNDWATER RISK ASSESSMENT > OVERVIEW OF GROUNDWATER POLLUTION RISK Dr Stephen Foster (IAH-Vice President) INTERNATIONAL ASSOCIATION OF HYDROGEOLOGISTS the global groundwater organisation

2. Le Monde a view of Britain from the south

3. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster GROUNDWATER POLLUTION RISK • strictly term ‘RISK’ (= hazard x impact) should relate to actual/potential consequence on human health or aquatic ecosystem or economic cost of mitigation (as in full EIA) • only possible to evaluate for major installations with : • comprehensive monitoring arrangements • detailed investigation permitting specific modelling (using all factors controlling contaminant generation/transport)

4. possible receptors

5. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster AQUIFER POLLUTION HAZARDa more flexible approach to ‘groundwater risk’ • best conceived as interaction between : • man-made subsurface contaminant load • intrinsic groundwater flow and pollutant attenuation capacity of strata overlying aquifer (or groundwater body) • needs to consider composite and cumulative effects • requires empirical ‘risk assessment methodologies’

6. AQUIFER POLLUTION HAZARD the conceptual scheme

7. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster GROUNDWATER POLLUTION RISK assessment methodologies • GENERIC MODELLING PACKAGES • for specific potential pollution sources (sanitary landfills, contaminated land, agricultural soil leaching, etc) • sometimes only estimate probable load generation • RISK-SCREENING TOOL COMBINATIONS • aquifer pollution vulnerability mapping • groundwater supply protection zone delineation • subsurface contaminant load surveys

8. GROUNDWATER RISK SCREENING TOOLS…….. needed to avoid prevent things unexpected arriving from above

9. SUBSURFACE CONTAMINANT LOAD AQUIFER VULNERABILITY GROUNDWATER POLLUTION HAZARD

10. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster AQUIFER POLLUTION VULNERABILITY development of concept • expression used intuitively in France from early 1980 • attempts to formalise definition and develop mapping schemes (GOD, DRASTIC, SINTACS, etc) in late 1980s • represents complex processes in simple fashion • significant limitations encountered including: • difficulty in representing layered aquifers • uncertain behaviour of some formations /contaminants

11. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster AQUIFER POLLUTION VULNERABILITY key conceptual issues for mapping • is use of ‘integrated vulnerability index’ a valid simplification? • should aquifer vulnerability include consideration of : • saturated zone transport/attenuation • shallow soil profile

12. CONTAMINANT ATTENUATION IN GROUNDWATER SYSTEMS each class of potential contaminant will be influenced to a different degree by the various processes

13. AQUIFER POLLUTION VULNERABILITYpractical definition of classes

14. AQUIFER POLLUTION VULNERABILITY best limited to consideration of unsaturated zone ?

15. GENERATION OF AQUIFER POLLUTION VULNERABILITY MAP USING THE GOD SYSTEM Foster, 1987

16. VADOSE (UNSATURATED ZONE) PREFERENTIAL FLOW contaminant transport consequences

17. Aller et al, 1987 • Depth to groundwater (X5) • natural Recharge rates (X4) • Aquifer media (X3) • Soil media (X2) • Topographic aspect (X1) • Impact (effect) of • vadose zone (X5) • hydraulic Conductivity (X3)

18. GROUNDWATER SUPPLY PROTECTION ZONES/PERIMETERS best way of dealing with capacity for contaminant transport, dilution and attenuation in the saturated zone

19. COMPONENTS OF GROUNDWATER POLLUTION hazard assessment and protection strategy

20. GROUNDWATER POLLUTION RISK ASSESSMENTestimation of subsurface contaminant load

21. SUBSURFACE CONTAMINANT LOAD POSH classification and ranking of point sources

22. INDUSTRIALLY- CONTAMINATED LAND generic groundwater pollution risk modelling packages now available

23. DIFFUSE POLLUTION FROM AGRICULTURAL LAND-USE Subsurface Pesticide Persistence

24. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster DIFFUSE POLLUTION FROM AGRICULTURAL LAND-USE approach to load assessment • concentration of nitrates/pesticides infiltrating from soil can be estimated using GIS technology from : • general description of soil characteristics (physical and biochemical) • land-use regime (agrochemical applications, livestock density, etc) • published/assumed properties of N-compounds + pesticides • historic climatic data (especially extreme events)

25. OVERVIEW OF GROUNDWATER POLLUTION RISKDr Stephen Foster CONCLUDING REMARKS • highly-dependent on ‘empirical screening methods’ to meet WFD/GWPD requirements on ‘groundwater bodies at risk’ • must be more consistent in our application/reporting of these methods and recognise their limitations • need to recognise close relation between groundwater vulnerability mapping/risk assessment methods and : • interpretation/thresholds for good groundwater chemical status • whether dealing with ‘average quality of aquifer replenishment’ or ‘average quality of groundwater storage’ • approaches to groundwater quality monitoring network design • specification of groundwater supply protection areas