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EZVI Injection Field Test Leads to Pilot-Scale Application
Citation:
SU, C. AND J. W. Quinn. EZVI Injection Field Test Leads to Pilot-Scale Application. IN: Technology News and Trends, US Environmental Protection Agency, Cincinnati, OH, (54):4-6, (2011).
Impact/Purpose:
Newsletter article for Technology News and Trends (a US EPA publication)
Description:
Testing and monitoring of emulsified zero-valent ironTM (EZVI) injections was conducted at Cape Canaveral Air Force Station’s Launch Complex 34, FL, in 2002 to 2005 to evaluate the technology’s efficacy in enhancing in situ dehalogenation of dense nonaqueous-phase liquid (DNAPL) [see September 2005 TNT]. Results from the small field test showed an average 71% reduction of trichloroethene (TCE) concentrations in groundwater of wells at depths of up to 25 feet below ground surface (bgs) and a 56% reduction in mass flux. Later in 2005, findings from the field test were used to begin a pilot-scale demonstration at the Marine Corps Recruit Depot in Parris Island, SC, with a focus on differentiating the technology’s degradation mechanisms and improving substrate delivery methods. As originally developed by the National Aeronautics and Space Administration (NASA), EZVI consists of food-grade surfactant, biodegradable vegetable oil, water, and nano- or micro-scale iron. The technology relies on presence of the water and oil to increase contact between the ZVI particles and DNAPL and consequently dissolve chlorinated volatile organic compounds (VOCs) and promote reductive dehalogenation. In addition to ZVI’s ability to chemically reduce the VOCs, the vegetable oil and surfactant serve as long-term electron donors for anaerobic biodegradation. The pilot-scale demonstration was conducted at the Depot’s Site 45, where earlier investigations revealed the presence of source-zone PCE DNAPL. Concentrations of the chlorinated daughter products TCE, cis-1,2-dichloroethene (cDCE), and vinyl chloride (VC) in the same wells were as high as 160 mg/L, 180 mg/L, and 13 mg/L, respectively. Post-injection sampling in downgradient wells 2.5 years after injection indicated that decreased PCE and TCE concentrations highly correlated to increases in degradation products and ethane in particular (Figure 1). By March 2009, total VOC mass in the pneumatic injection plot had decreased approximately 86%, from 38 kg to 5 kg. Based on soil and groundwater sample analyses, treatment resulted in an estimated 63% reduction in the sorbed and dissolved phases and 93% reduction in the PCE DNAPL mass. Results from integral pump tests in downgradient wells and from measurements in multilevel well transects showed mass flux reduction values exceeding 85% for both PCE and TCE and a 145% to 2271% increase for ethene.
