Field pilot scale studies have demonstrated that co-solvent-enhanced in situ extraction can remove residual and free-phase nonaqueous phase liquid (NAPL), but may leave levels of contaminants in the ground water and subsurface formation higher than regulatory requirements for closure of a site. Various methods of improving delivery and recovery of co-solvent mixtures and of facilitating in situ mixing of these light remedial fluids with resident contaminants have been proposed and are being investigated. However, it is unlikely that these improvements alone will permit regulatory goals to be achieved via enhanced NAPL solubilization or mobilization. Recent laboratory and field tests have examined the feasibility and benefits of coupling co-solvent to stimulate in situ biotreatment following partial dense nonaqueous phase liquid (DNAPL) source removal by alcohol-induced dissolution was evaluated at a former dry cleaner site in Jacksonville, Florida. Contaminant and geochemical monitoring at the site suggests that biotransformation of the tetrachloroethylene (PCE) was enhanced and significant levels of cis-dichloroethylene (cis-DCE) were produced in areas exposed to residual co-solvent.