Solvent release into a sandy aquifer 3: enhanced dissolution by methanol injection

A field experiment involving a release of 5 litres of a mixture of chlorinated solvents (0.5 l of chloroform, 2.0 l of trichloroethylene, and 2.5 l of tetrachloroethylene) was carried out in a sandy, unconfined, shallow aquifer at Canadian Forces Base Borden, east of Toronto, Ontario, Canada. The dissolution of the chlorinated solvents into the groundwater was studied in detail for 220 days, then a methanol/water mixture was injected to study the possible enhancement of the dissolution. An effect of the methanol injection was only observed at a few sampling points, likely due to the distribution of the solvent as a laterally extensive, thin pool. This investigation shows that it is crucial to know the exact location of the dense nonaqueous phase liquids (DNAPL) in the subsurface when designing and performing remedial techniques at contaminated sites.