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DETERMINATION OF RATES AND EXTENT OF DECHLORINATION IN PCB-CONTAMINATED SEDIMENTS DURING MONITORED NATURAL RECOVERY
Citation:
BATTELLE. DETERMINATION OF RATES AND EXTENT OF DECHLORINATION IN PCB-CONTAMINATED SEDIMENTS DURING MONITORED NATURAL RECOVERY. U.S. Environmental Protection Agency, Washington, DC, EPA/600/S-08/012, 2008.
Impact/Purpose:
To evaluate the long-term recovery of polychlorinated biphenyl-contaminated sediments via reductive dechlorination, and to evaluate Monitored Natural Recovery processes in aquatic sediments, during field studies conducted at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site in Pickens County, SC.
Description:
This "Sediment Issue" summarizes investigations carried out by the National Risk Management Research Laboratory (NRMRL) of U.S. EPA to evaluate the long-term recovery of polychlorinated biphenyl (PCB)-contaminated sediments via reductive dechlorination. The magnitude, extent, and rates of ortho and meta plus para dechlorination were determined as a function of sediment depth and time. PCB sources and alteration patterns were characterized using congener fingerprinting and polytopic vector analysis (PVA). These data were generated during NRMRL field studies conducted in cooperation with U.S. EPA Region 4 to evaluate monitored natural recovery (MNR) at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site in Pickens County, SC. Under anaerobic conditions, the primary metabolic pathway for PCBs is reductive dechlorination in which chlorine removal and substitution with hydrogen by bacteria result in a reduced organic compound with fewer chlorine molecules. Average dechlorination rates at Lake Hartwell assuming a uniform PCB concentration of 60 mg/kg were 0.174 and 0.132 nmole Cl/g sediment per week for transect cores collected in 2000 and 2001, respectively, The rate determined for the 2001 cores equates to an amount of time for complete chlorine removal of about 33 years. PVA end-member (EM) patterns were compared with known source patterns (i.e., Aroclors or Aroclor mixtures) and literature-reported alteration patterns. As an example, the congener profiles measured for EM-1 displayed strong similarities with 50/50 source mixtures of Aroclor 1248/1254 and Aroclor 1242/1254. These sudies indicated that PCB dechlorination data can be a valuable resource in assessing the extent of natural recovery achieved and PCB congener fingerprinting and multivariate receptor modeling (such as PVA) can be used as exploratory data analysis tools to characterize PCB sources and alteration patterns. PVA can also be employed to determine the vertical and lateral distributions of PCB source and dechlorination patterns.