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In the first phase of this project (Phase I), two 11.7 cubic meter Experimental Controlled Release Systems (ECRS), packed with sandy model aquifer material and amended with tetrachloroethene (PCE) DNAPL source zones, were operated in parallel with identical flow regimes and electron donor amendments. Hydrogen Releasing Compound-trademark (HRC), and later dissolved lactate, served as electron donors to promote dechlorination. One ECRS was bioaugmented with an anaerobic dechlorinating consortium directly into the source zone, and the other served as a control (biostimulated only) to determine the benefits of bioaugmentation. The presence of halorespiring bacteria in the aquifer matrix prior to bioaugmentation, shown by nested PCR with phylogenetic primers, suggests that dechlorinating catabolic potential may be somewhat widespread. PCR analyses demonstrated that the bacteria present in the culture used for bioaugmentation in the ECRS prevailed for almost a year. Unfortunately, even with Dehalococcoides present, complete dechlorination to ethene was achieved at minimum (<1 micrometer). Results demonstrated that the low concentration of ethene produced in this first phase was not due to washout of the dechlorinating organisms. It was also demonstrated that as long as the electron acceptor was not limiting, there was greater energy flow to the dechlorinating populations than to the methanogens. Overall, the results obtained in the Phase I corroborate that source zone reductive Dechlorinating of PCE is possible at near field scale, and that a system bioaugmented with a competent halorespiring consortium can enhance DNAPL dissolution and dechlorination processes at significantly greater rates than in a system that is biostimulated only., The original document contains color images. Performed in cooperation with Georgia Institute of Technology, Atlanta, GA, and Universidade Federal de Santa Catarina, Brazil.