Thursday, August 14, 2008 - 10:00 AM
S141
Treatment of Metals in Groundwater Using an Organic-Based Sulfate-Reducing Permeable Reactive Barrier
Ralph D. Ludwig, Office of Research and Development, U.S. Environmental Protection Agency, 919 Kerr Research Dr., Ada, OK 74820
A pilot permeable reactive barrier (PRB) consisting of a mixture of leaf compost, zero-valent iron (ZVI) filings, limestone and pea gravel was installed at a former phosphate fertilizer manufacturing facility in Charleston, S.C. Groundwater at the site is contaminated with arsenic and heavy metals resulting from acid rock drainage. The PRB is designed to treat arsenic and heavy metals in the groundwater by promoting microbially-mediated sulfate reduction and subsequent sulfide precipitation. In addition, the PRB is designed to generate alkalinity to aid in neutralizing acid-impacted sediments down gradient of the PRB. Performance monitoring conducted over a period of 30 months indicated effective treatment of arsenic, lead, and cadmium with concentrations up to 126 mg/L, 3.23 mg/L, and 2.10 mg/L, respectively entering the PRB being treated to average concentrations of less than 0.04 mg/L, 0.009 mg/L, and 0.003 mg/L, respectively within the PRB. Alkalinity in the ground water increased from 0 mg/L in the up-gradient groundwater to up to 630 mg/L as CaCO3 within the PRB imparting an acid neutralizing capacity to the PRB discharge. The presence of sulfate reducers and observed 34S enrichment within the PRB provided strong supporting evidence of sulfate reduction. Low sulfide concentrations measured in the PRB pore water suggest sulfide is likely being rapidly precipitated out within the PRB upon reaction with metals and excess dissolved iron.
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See more of The Annual Meeting and Exhibition 2008 (August 10 - 14, 2008)