Emulsified-Oil Biobarrier Provides Long-Term Treatment of Perchlorate/VOC Plume

Security Technology Certification Program (ESTCP) evaluation of a PRB containing emulsified oil substrate (EOS®). The pilot study was initiated in 2003 at the Alliant Techsystems, Inc., facility in Elkton, MD, to evaluate effectiveness of EOS technology for enhancing biodegration of perchlorate and chlorinated solvents. A single dose of low solubility, low viscosity, and slowly biodegradable edible-oil emulsion was injected directly into the contaminated aquifer. Post-treatment monitoring indicates that introduction of this reactive medium provided sufficient organic carbon to support biological degradation of target contaminants and consistently maintain contaminant concentrations below target levels for nearly three years.

Historical activities at the site include manufacturing of solid propellant rocket motors. In the 1980s, routine groundwater monitoring revealed ground-water contamination resulting from a permitted hazardous waste surface impoundment. Site conditions amenable to an EOS PRB included a shallow aquifer located 5-15 feet below ground surface (bgs) consisting of silty sand and gravel with moderate permeability (~29 ft/day), and a groundwater flow velocity of approximately 100 ft/year. Demonstration ease was enhanced by well-defined distribution of contaminants in a commingled plume emanating from a closed surface-water impoundment. Average concentrations of target contaminants in the treatment area were 9,000 mg/L perchlorate, 11,000 mg/L 1,1,1-trichloroethane (TCA), 50 mg/L perchloroethene (PCE), and 90 mg/L trichloroethene (TCE).

The demonstration was designed to evaluate distribution of the emulsified oil sufficiently to form a PRB perpendicular to ground-water flow, injection impacts on aquifer permeability and ground-water flow paths, and changes in contaminant concentrations and biodegradation indicators during ground-water flow through the biobarrier. The technology employs emulsified-oil concentrate consisting of food-grade soybean oil, surfactants, amino acids, and vitamins blended to form a stable emulsion with small, uniformly sized oil droplets. Once injected, the oil droplets adhere to sediment surfaces and form a residual oil phase that provides a carbon source and electron donor for long-term in-situ anaerobic biodegradation of contaminants.

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