Detection of point sources of contamination by chlorinated solvents: a case study from the Chalk aquifer of eastern England

Abstract

Groundwater contamination by chlorinated solvents such as trichloroethene is of increasing concern in the UK. This paper describes a case study of chlorinated solvent contamination of the Chalk aquifer at a groundwater supply source in eastern England. The investigations comprised two phases: the first phase focused on the extent and nature of the contamination within the main Chalk aquifer (both in the fissures and in the Chalk matrix); and the second phase targeted the sources of contamination through detailed sampling of the unsaturated drift at suspect sites. The volatile nature of the organic contaminants required special hygiene procedures during drilling and sampling to avoid cross-contamination between boreholes, or loss of contaminants in the samples collected. Four potential sources of contamination were identified within an industrialized area about 1 km up hydraulic gradient from the contaminated well. However, the contamination was found to be extremely localized, with closely spaced investigation boreholes at individual sites giving highly varied results. To be successful, investigation boreholes had to target precise locations where these chemicals were known or suspected to have been used or stored. Therefore, a key aspect of the investigation was a solvent usage survey prior to each phase of drilling.chlorinated solvents: a case study from the Chalk aquifer of eastern England.