Prioritisation of abstraction boreholes at risk from chlorinated solvent contamination on the UK Permo-Triassic Sandstone aquifer using a GIS.

A 250 km2 area of the Permo-Triassic Sandstone aquifer in the West Midlands of England, UK, was selected as a test region for the development of a geographic information system (GIS)-based risk assessment methodology that incorporates contaminant source, groundwater vulnerability and groundwater abstraction catchment elements in order to prioritise areas and boreholes potentially at risk from chlorinated solvent pollution on a regional scale. Factors incorporated in the vulnerability assessment include the nature of soils, presence or absence of superficial or glacial deposits, fault density and depth to water table. ARCVIEW GIS was employed with a simple ranking system from which the derived vulnerability assessment index was combined with current chlorinated solvent user industry data and source protection zone components. Results indicate the presence of high-risk areas in urban locations where locally dense distributions of chlorinated solvent user industries combine with high vulnerability aquifers within the catchment of supply boreholes. Ranking of catchment-specific risk reveals the abstraction points under greatest stress. The proposed methodology has applications as a regional-scale initial screening tool to guide site selection for regulatory inspections and assist in prioritising monitoring strategies for existing boreholes. Future developments will provide guidance for locating new urban boreholes in areas of lowest risk.