Metal-Enhanced Dechlorination of Volatile Organic Compounds Using and In-Situ Reactive Iron Wall

EnviroMetal Technologies, Inc. (ETI), of Guelph, Ontario, Canada has commercialized a metal-enhanced dechlorination technology that the University of Waterloo, Canada developed to treat aqueous media contaminated with chlorinated volatile organic compounds (VOCs). The technology employs an electrochemical process that involves the oxidation of a reactive, granular iron medium to induce reductive dechlorination of chlorinated VOCs. The Superfund Innovative Technology Evaluation (SITE) Program evaluated an in-situ application of the technology during a 6-month demonstration at a confidential site in central New York in 1995. For the demonstration of the in-situ system, the technology was constructed as a subsurface, reactive iron wall that fully penetrated a shallow sand and gravel aquifer. The top of the wall was above the highest average seasonal groundwater level, about 3 feet below grade, and was covered with a layer of native topsoil. The wall extended downward from the top of the saturated zone and was situated on top of an underlying, confining clay layer. The reactive iron wall, referred to as the “gate,” was oriented perpendicular to the groundwater flow direction and was flanked by impermeable sheet piling wings which also fully penetrated the aquifer. The sheet piling formed a “funnel,” creating a hydraulic barrier that diverted groundwater flow from a 24-foot-wide upgradient area through the gate, and prevented untreated groundwater from flowing around the gate and mixing with treated groundwater on the downgradient side. During the demonstration, SITE Program personnel collected independent data to evaluate the technology’s performance with respect to primary and secondary objectives. Groundwater samples were collected at locations on the upgradient (influent) and downgradient (effluent) sides of the iron, and also from locations within the iron. The groundwater samples were analyzed for VOCs to evaluate the technology’s ability to reduce chlorinated VOC concentrations to applicable regulatory levels. The efficiency with which the system removed certain chlorinated VOCs was evaluated. Other data were collected to provide information about the dechlorination process, as well as costs and operating and maintenance requirements for the system. The results of the sample analyses indicated that the technology significantly reduced the concentrations of chlorinated VOCs in groundwater passing through the gate. These chlorinated VOCs included trichloroethene (TCE), cis-1,Zdichloroethene (cDCE), and vinyl chloride (VC). All average critical parameter effluent concentrations, and 86 out of 90 individual critical parameter measurements, achieved the applicable U.S. Environmental Protection Agency (EPA) maximum contaminant levels or New York State Department of Environmental Conservation target standards. Removal efficiencies for TCE, cDCE, and VC were consistently greater than 90 percent. The results indicated no decrease in removal efficiency or other significant changes in system performance over the 6-month demonstration period. EPA SITE Program personnel prepared this Innovative Technology Evaluation Report (ITER) to present the results of the SITE Program demonstration. The ITER evaluates the ability of the in-situ application of the metal-enhanced dechlorination technology to treat chlorinated VOCs in contaminated groundwater based on the demonstration results. Specifically, this report discusses performance and economic data collected by SITE Program personnel, and also presents case studies and additional information about the technology provided by ETI.