Long-term monitoring of enhanced natural attenuation effect and subsurface biological environment change

At a chlorinated aliphatic hydrocarbon (CAH)-contaminated site, Hydrogen Release Compound® (HRC®) was injected into the aquifer for > 3 yr to form a bio-barrier for enhancing in situ biological reductive dechlorination. The contaminated site had used tetrachloroethylene (PCE) for many years and PCE in groundwater was as the source contaminant at the site. Its daughter compounds trichloroethylene (TCE) and cis-1,2-dichloroethylene (cis-DCE) also were detected from groundwater samples. After the injection of HRC® into the aquifer, obvious acceleration of PCE, TCE, and cis-DCE degradation was obtained. Portion of the parent compounds were completely degraded to ethylene. HRC® in the contaminated aquifer increased the degradation coefficients of CAH significantly. No matter whether Dehalococcoides sp. bacteria was detected or not, degradation of CAH showed a stable state. This stable degradation of CAH on the site could be related to some other bacteria other than Dehalococcoides sp. bacteria. This is an abstract of a paper presented at the proceedings of the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).