Chlorinated solvents in the Birmingham aquifer, UK: 1986-2001

The value of using an abstraction well-based monitoring approach to diagnose an aquifer's chlorinated solvent condition is successfully demonstrated for the urbanized Birmingham aquifer, UK. Data from surveys conducted a decade apart (1986-89 and 1998-2001) were compared. Trichloroethylene (TCE) was the principal solvent detected at 78% of abstraction sites in 1987. This reduced to 56% of sites by 1998. The decline in percent occurrence is attributed to closure of abstractions associated with former solvent-user industries rather than signifying an improvement in aquifer quality. Indeed, comparison of abstractions common to both surveys indicated greater contamination in the more recent survey that was attributed to the persistency of historical dense nonaqueous-phase liquid (DNAPL) source zones. Persistence of perchloroethylene (PCE) relative to TCE was observed and ascribed to its lower solubility and greater sorption. Biodegradation was evident, but insufficient to prevent parent solvents from being detected at half of the non-solvent user sites sampled in 1998. Nevertheless solvent-free water can still be abstracted. This may, however, become increasingly difficult as industrial recession has caused closure of many solvent-user industry abstractions previously thought to have been undertaking inadvertent pump-and-treat of plumes. Such plumes are now able to more freely migrate throughout the aquifer. The observed persistency of solvent contamination spanning a decade suggests that the European Water Framework Directive (WFD) requirement to obtain good chemical status is unlikely to be achieved within the required timescales for solvent-contaminated urban aquifers.