A detailed investigation of contamination by chlorinated solvents of the Chalk Aquifer underlying the towns of Luton and Dunstable was undertaken to assess the extent, causes and mechanisms of pollution. The research programme incorporated land‐use surveys, regional groundwater surveys, monitoring of groundwater abstraction points and aquifer profiling by means of the drilling of observation boreholes, the analysis of the recovered core material and the depth sampling of these and other boreholes.
Low‐level solvent contamination of the Chalk Aquifer was found to be widespread with ‘hotspots’of higher concentrations. At the drilling sites, both the saturated and unsaturated zones were contaminated with solvents, although free product was not observed. The presence of an additional contaminant, oil, at some sites was noted to influence the distribution of solvents within the aquifer.
Clean‐up of the aquifer is not a practical option, and treatment of the groundwater at the abstraction points has been adopted.
Summary
An examination has been made of groundwater related problems experienced in the Forest of Dean since abandonment of the major collieries in 1965. Careful planning prior to abandonment of collieries can reduce the number of poor quality discharges, and so substantially limit surface water pollution. Small-scale mining activity continuing after major colleries have been abandoned can have a serious hydrogeological effect by removal of
in situ
coal from drainage barriers designed to promote free drainage of the mines. In association with the deterioration of lined river channels which retard surface water infiltration, this disruption of subsurface can result in a drainage significant loss of summer base-flow from surface rivers.
Two case histories show that safe disposal of wastes to voids in mined Coal Measures aquifers is possible. Prediction of the hydrogeological behaviour of the mined aquifer is, however, difficult because of the possibility of unrecorded workings, random collapse and associated ponding, and uncertainty over the hydrological behaviour of the coal barriers. Direct investigation of the groundwater flow regime using boreholes and water tracing techniques is recommended.
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