Biodegradation of <i>cis</i>-Dichloroethene and Vinyl Chloride in the Capillary Fringe

Volatile chlorinated compounds are major pollutants in groundwater, and they pose a risk of vapor intrusion into buildings. Vapor intrusion can be prevented by natural attenuation in the vadose zone if biodegradation mechanisms can be established. In this study, we tested the hypothesis that bacteria can use <i>cis-</i>dichloroethene (<i>cis</i>-DCE) or vinyl chloride (VC) as an electron donor in the vadose zone. Anoxic water containing <i>cis</i>-DCE or VC was pumped continuously beneath laboratory columns that represented the vadose zone. Columns were inoculated with <i>Polaromonas</i> sp. strain JS666, which grows aerobically on <i>cis</i>-DCE, or with <i>Mycobacterium</i> sp. JS60 and <i>Nocardiodes</i> sp. JS614 that grow on VC. Complete biodegradation with fluxes of 84 ± 15 μmol of <i>cis</i>-DCE·m^–2·hr^–1 and 218 ± 25 μmole VC·m^–2·h^–1 within the 23 cm column indicated that microbial activities can prevent the migration of <i>cis</i>-DCE and VC vapors. Oxygen and volatile compound profiles along with enumeration of bacterial populations indicated that most of the biodegradation took place in the first 10 cm above the saturated zone within the capillary fringe. The results revealed that <i>cis</i>-DCE and VC can be biodegraded readily at the oxic/anoxic interfaces in the vadose zone if appropriate microbes are present