ABSTRACT: In situ bioremediation is ongoing at a former manufacturing facility in Portland, Oregon. Shallow groundwater at the site was impacted by chlorinated solvents, primarily trichloroethene and degradation products cis-1,2-dichloroethene and vinyl chloride. In situ chemical oxidation treatment was completed in 2003 via the injection of sodium permanganate in source areas. Subsequent stimulation of in situ biological treatment via reductive dechlorination was evaluated and found to be viable. Emulsified vegetable oil with vitamin B12 and other nutrients (EOS® 598 B42) was injected in March and April 2005. Injections were completed over a depth range of 25 to 40 feet (7.6 to 12.2 m) using push probe equipment with an air diaphragm pump. Treatment costs are provided. Regular groundwater monitoring has been conducted following the initiation of the bioremediation treatment. Nearly two years of post-injection groundwater monitoring data are presented. These data show that the emulisfied oil continues to provide increased total organic carbon concentrations in the injection area wells and that concentrations of chlorinated ethenes in the treatment zone have decreased more than 99%. This success has been achieved despite some parameters (e.g., ORP) being outside of optimal ranges for reductive dechlorination. Continued groundwater sampling will be conducted to monitor the longevity of the emulsified oil product and the progress toward achieving site remediation goals.