Bioremediation of vinyl chloride (VC) contamination in groundwater could be mediated by three major bacterial guilds: anaerobic VC-dechlorinators, methanotrophs, and ethene-oxidizing bacteria (etheneotrophs) via metabolic or cometabolic pathways. We collected 95 groundwater samples across 6 chlorinated ethene-contaminated sites and searched for relationships among VC biodegradation gene abundance and expression and site geochemical parameters (e.g., VC concentrations). Functional genes from the three major VC-degrading bacterial guilds were present in 99% and expressed in 59% of the samples. Etheneotroph and methanotroph functional gene abundances ranged from 10 to 10 genes per liter of groundwater among the samples with VC reductive dehalogenase gene (bvcA and vcrA) abundances reaching 10 genes per liter of groundwater. Etheneotroph functional genes (etnC and etnE) and VC reductive dehalogenase genes (bvcA and vcrA) were strongly related to VC concentrations (p < 0.001). Methanotroph functional genes (mmoX and pmoA) were not related to VC concentration (p > 0.05). Samples from sites with bulk VC attenuation rates >0.08 year contained higher levels of etheneotroph and anaerobic VC-dechlorinator functional genes and transcripts than those with bulk VC attenuation rates <0.004 year. We conclude that both etheneotrophs and anaerobic VC-dechlorinators have the potential to simultaneously contribute to VC biodegradation at these sites.

A production well, called the south well, is located behind the white trailer in the middle of the photograph. This well and two other production wells pump groundwater from the sand and gravel aquifer to elevated storage tanks, such as the two shown in the background. In 1985, contaminants were detected in samples collected from the south well. To help understand groundwater flow in the underlying sand and gravel aquifer, the U.S. Geological Survey completed borehole geophysical logging at multiple locations, including the deepest monitoring well, WHF-05-OW-1D, shown here under the blue awning.

No abstract

A sulfuric acid leak in 1988 at a chloroethene-contaminated groundwater site at the Naval Air Station Pensacola has resulted in a long-term record of the behavior of chloroethene contaminants at low pH and a unique opportunity to assess the potential impact of source area treatment technologies, which involve acidification of the groundwater environment (e.g., Fenton's-based ever, demonstrated only a limited mineralization to 14 CO 2 and 14 CO, which was attributed to abiotic degradation because no significant differences were observed between experimental and autoclaved control treatments. These results indicated that biotic and abiotic mechanisms contributed to chloroethene attenuation in the acid plume at NAS Pensacola and that remediation techniques involving acidification of the groundwater environment (e.g., Fenton's-based source area treatment) do not necessarily preclude efficient chloroethene degradation. O

Laboratory characterization studies, one‐dimensional flow‐through studies, and numerical model simulations were conducted to examine site conditions and system features that may have adversely affected in situ chemical oxidation (ISCO) performance at the Naval Training Center’s (NTC) Operable Unit 4 located in Orlando, Florida, and to identify potential ISCO system modifications to achieve the desired remediation performance. At the NTC site, ISCO was implemented using vertical injection wells to deliver potassium permanganate into a ground water zone for treatment of tetrachloroethylene and its breakdown products. However, oxidant distribution was much more limited than anticipated. Characterization studies revealed that the ground water zone being treated by ISCO was very fine sand with a small effective particle size and low uniformity coefficient, along with a high organic carbon content, high natural oxidant demand (NOD), and a high ground water dissolved solids concentration, all of which contributed to full‐scale ISCO application difficulties. These site conditions contributed to injection well permeability loss and an inability to achieve the design oxidant injection flow rate, limiting the actual oxidant distribution at the site. Flow‐through experiments demonstrated that more favorable oxidant delivery and distribution conditions are enabled by applying a lower oxidant concentration at a faster delivery rate for a greater number of pore volumes. Numerical simulations, run for a variety of conditions (injection/extraction well flow rates, injected oxidant concentration, amount of NOD present, and NOD oxidation rate), also revealed that low–oxidant concentration injection at a high flow rate is a more effective method to deliver the required mass of oxidant to the target treatment zone.