- 1,1,1-Tricholorethane (1,1,1-TCA), a widely used industrial solvents, is one of the most common subsurface contaminants. Transformation processes in the subsurface can result in the production of 1,1-dichioroethane (1,1-DCA) and 1,1- dichioroethene (l,1-DCE) from 1,1,1-TCA contamination, resulting in plumes of mixed chlorinated aliphatic hydrocarbons (CAHs). A butane-utilizing microorganism, strain 1 83BP, with the ability to cometabolically transform 1,1,1 - TCA, 1,l-DCA, and 1,1-DCE was isolated from environmental samples taken from a CAH contaminated site. In laboratory microcosm studies (Rungkamol, 2001; Mathias, 2002; Lim, 2003), the results showed that microcosms bioaugmented with strain 1 83BP and fed butane as a primary substrate rapidly transformed 1,1 -DCE, followed by slower transformation of 1,1 -DCA and 1,1,1 -TCA when all three CAHs were present. A 1-kb segment of the 16S rRNA gene sequence of strain 183BP was found to be identical to that of Rhodococcus sp. USAN-12 (Genbank accession number AF420413). Two bioaugmentation treatment tests with strain 1 83BP as inoculum were conducted at the Moffett Federal Airfield In-Situ Bioremediation Test Site (Moffett Field), Mountain View, CA. Also, a soil colunin packed with aquifer solids and groundwater obtained from Moffett Field was inoculated with strain 1 83BP and operated under conditions similar to those used in the field tests. Field groundwater samples and soil colunm effluent samples were analyzed using techniques based on 16S rRNA gene analysis. 183BP-specific primers were designed and used in real-time SYBR Green I PCR analyses to detect and quantify the inoculated microorganisms in the subsurface. Dynamics of the bacterial community composition were investigated using terminal restriction fragment length polymorphism (T-RFLP) methods and statistical analysis. During the first bioaugmentation test in the absence of 1,1-DCE, maximum treatment efficiencies for TCA and DCA were approximately 80% and 96%, respectively in the bioaugmented well leg, while essentially no transformation occurred in the non-bioaugmented control leg. During the effective treatment period, the 1 83BP cell concentration was above 900 cells/ml in groundwater obtained 0.5 m from the injection well. In the second bioaugmentation test, 1,1 -DCE was added to the influent CAH mixture and was effectively transformed in the bioaugmented well leg. Although 93% of the influent 1,1-DCE was transformed, 1,1 -DCA and 1,1,1 -TCA removal efficiencies were significantly reduced compared to the test in the absence of 1,1-DCE. The 183BP cell concentration was almost 1-log-order higher than that of the first test and clear spatial distribution of the cells among the monitoring wells was observed. The bioaugrnented strain 1 83BP was not observed in T-RFLP analyses conducted on groundwater samples during either bioaugmentation test. The groundwater bacterial community profiles were alternately dominated by two peaks, 277-hp during the early stages of amendments and 126-hp during the later stages of both tests. In the soil column, maximum treatment efficiencies for TCA and DCE were approximately 96% and 77%, respectively. Microbial results indicated that the decline in TCA concentrations was concomitant to an increase in the concentration of strain 1 83BP cells. The bacterial community had greater species diversity than field samples and did not follow the same succession trend as the field samples. However, addition of 1,l-DCE in the feed to the column resulted in a similar reduction of 1,1-DCA and 1,1,1-TCA transformation efficiencies as that observed in the field studies.