A microcosm study was used to assess the potential for in situ natural or enhanced bioremediation at a chloroethane- (i.e., tetrachloroethane, TeCA) and chloroethene-contaminated (i.e., tetrachloroethene, PCE; trichloroethene, TCE) groundwater in Northern Italy. All the live microcosms were positive for dechlorination, indicating the presence of an active native dechlorinating population in the subsurface. All the tested electron donors (i.e., yeast extract, lactate, butyrate, hydrogen) promoted enhanced dechlorination of chlorinated contaminants. Lactate- and butyrate-amended microcosms performed the best, and also dechlorinated the solvents past cis-dichloroethene (cis-DCE). The microcosm bioaugmented with a PCE-dechlorinating mixed culture containing Dehalococcoides spp. dechlorinated groundwater contaminants to DCE, vinyl chloride (VC), and ethene (ETH). In conclusion, results from this microcosm study indicate the potential for enhancing full dechlorination at the contaminated site, through a proper addition of a suitable electron donor (e.g., lactate or butyrate) and/or through bioaugmentation with a Dehalococcoides-containing culture.