A unique groundwater treatment program has been initiated at a MA site, which has a large plume with low concentrations (2 to 29 ppb) of vinyl chloride (VC). The bioremediation approach used at the site includes in-situ, aerobic biostimulation treatment using the iSOC system to deliver oxygen and ethene by infusion along with the addition of mineral nutrients. This remediation is likely the first in the U.S. to be based on ethenotrophic bioremediation. Recent research has indicated that naturally occurring bacteria are capable of growth on both ethene and VC (Coleman and Spain 2003, J. Bact.185:5536) and that ethene-degrading bacteria are able to degrade low concentrations of VC more efficiently than aerobic methanotrophs or anaerobic bacteria such as Dehalococcoides ethenogenes.
Previous laboratory microcosm studies reported in a presentation at the Battelle Bioremediation Conference in 2005 had shown the complete degradation of very low ppb levels of VC in groundwater under ethenotrophic conditions. This suggested that addition of ethene to the site groundwater would stimulate the growth of ethene-consuming bacteria to sufficiently high numbers to enable them to biodegrade very low concentrations of VC as demonstrated in microcosm tests. This approach is designed to overcome substrate limited conditions at the site by providing ethene as a co-substrate for growth-coupled complete biodegradation of the contaminant.
A monitoring program was designed to evaluate the effectiveness of the delivery of oxygen and ethene gases via infusion wells as part of the treatment optimization program. Groundwater monitoring includes measurement of mineral nutrients dissolved gases including O2 and ethene, VC and periodic enumeration of ethene-oxidizing/VC-oxidizing bacteria.
An overview of the substrate delivery system design and performance monitoring program will be presented along with an assessment of remedial system performance.