USING A HIGH ORGANIC-MATTER PERMEABLE REACTIVE BARRIER TO REMEDIATE TRICHLOROETHYLENE-CONTAMINATED GROUNDWATER AT THE BEAVER DAM ROAD LANDFILL
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Trichloroethylene (TCE) is an effective industrial degreaser and known carcinogen. It was frequently improperly disposed of and has become one of the most common groundwater and soil contaminants in the USA. Clean up continues to be difficult due to its physical and chemical properties. TCE and several of its degradation products were detected in the groundwater of the Beaver Dam Road Landfill (Beltsville, MD) at concentrations above their maximum contaminant levels (MCLs). The US Department of Agriculture-Agricultural Research Service together with the University of Maryland, College Park and BMT Designers and Planners designed a permeable reactive barrier, or biowall, to remediate the contaminated groundwater. A series of batch reactor studies were conducted at 12°C to examine biowall fill-material combinations including the effects of zero-valent iron (ZVI) and glycerol amendments. Headspace samples were analyzed over the course of several months to monitor TCE degradation. An unamended, 4:3 mulch-to-compost combination was chosen based on no detectable TCE at the conclusion of the experiment. To increase the biowall degradation capacity, microbial infiltration and colonization of the structure were also studied. PCR, qPCR, and next-generation sequencing were used to survey the site’s indigenous population for dechlorinating clusters. Numerous clusters were identified affirming the use of the native population for bioaugmentation efforts. The ability of the biowall to support said community was investigated by monitoring continuously-fed column reactors containing biowall material spiked with a commercially-available, surrogate population, with and without a 5 mg/L dose of ZVI. The groundwater-fed column sans ZVI had the greatest Dehalococcoides population and while ZVI without biostimulation did decrease the overall population, it did not cause a statistically significant difference. Thus, if ZVI were to be used as a future biowall amendment, biostimulation would not be required to maintain a dechlorinating population. A sacrificial carbon source may be necessary to slow the biological degradation of the biowall’s organic fill-material. These findings will be utilized in future remediation and/or biowall expansion plans to fully employ the site’s natural resources. The biowall was constructed in July 2013 containing the 4:3 mulch-to-compost ratio and has reduced the upstream TCE concentration by ~90%.