Solid Waste Management Unit (SWMU) 12 is located within the lower east-central portion of NWS Charleston in the floodplain of the Cooper River. The total area of SWMU 12 is approximately 3 acres. The site is relatively flat with a total relief ranging from 3.0 to 8.5 feet above mean sea level. Historically, 4 structures were located at the site. Three of the buildings were demolished and removed in August and September 2002. The operational area of the site is completely fenced. The area outside of the fence line consists of forest, wetlands, and marshes.

Site Environmental History

Past operations at SWMU 12 included the treatment of wooden ammunition boxes using pentachlorophenal (PCP). A RCRA Facility Investigation (RFI) was conducted from February through June 1998, with a supplemental investigation effort conducted from June to August 2000. The site investigation results indicated the presence of high concentrations of chlorinated volatile organic compounds (VOCs) in the groundwater at SWMU 12. The contaminated groundwater plume was found to be migrating eastward with a minor component migrating north. The majority of the observed chlorinated VOCs were found within the shallow aquifer, shallower than 18 feet below ground surface (bgs). The deep aquifer has little or no impact. A former 500-gallon underground storage tank (UST) was found as the source of chlorinated VOC contamination of groundwater. The last determined use of the UST was 1979 to store solvents associated with the wood treatment activities. The tank contents were pumped out in 1998. The UST was excavated and removed in September 1999. Two holes, approximately ¼-inch diameter, located approximately 6 inches above the bottom of the tank, were observed during the removal of the tank. These holes allowed the free exchange of the tank contents with groundwater. During removal of the UST, the contents of the tank drained into the excavation and was observed on the groundwater surface in the excavation. Elevated chlorinated solvents were detected from a sample of the groundwater collected from the excavation. The highest detected concentrations of total VOCs were detected in groundwater samples collected in the vicinity of the former UST.