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Work Plan, PFAS Site Inspection <br />Naval Computer and Telecommunications Station Stockton, California Background Information <br /> 2-10 DCN: TRBW-0202-5183-0010 <br />The Navy conducted a surface water and sediment site investigation (SWSSI) during June 1995 <br />and March 1996 to verify the presence of contaminants detected in drainage channels at NCTS <br />Stockton (PRC 1997). The results of the SWSSI indicated that sediment in the upper dry reach <br />contained arsenic, cadmium, copper, 4,4’-dichlorodiphenyldichloroethene (4,4’-DDE), lead, <br />mercury, silver, and zinc above ecological screening criteria and ambient concentrations. In <br />addition, arsenic, lead, and 4,4’-DDE concentrations exceeded industrial USEPA preliminary <br />remediation goals. The sediment contamination originated with discharges from documented IR <br />sites at NCTS Stockton as well as nonpoint sources. Runoff from throughout NCTS Stockton <br />flowed to the drainage channel system and carried the contamination into the sediment. <br />Contaminated sediment in the upper dry reach of the drainage system was mobilized by seasonal <br />runoff. This seasonal increase in water flow mobilized the contaminants in the sediment, flushing <br />them into the lower inundated reach of the drainage system. The SWSSI recommended removal <br />of sediment during maintenance dredging (PRC 1997). <br />In August 1999, the Navy conducted maintenance dredging of the unlined drainage channel wet <br />reaches and removed the sediment down to the native clay at the base of the drainage channel at <br />NCTS Stockton. About 20,470 linear feet of unlined channels were dredged, removing <br />contaminated sediment down to the native soil interface. Dredge spoils were placed on adjacent <br />banks, characterized, and transported to an appropriate facility for disposal. In addition, about <br />2,570 linear feet of culverts were cleaned. About 19,340 tons of sediment were removed for <br />disposal (Tetra Tech EMI 2001). Additionally, a Time Critical Removal Action was conducted in <br />2000 to install sediment traps within the dry reaches of the storm water system, located in the <br />northeastern portion of the facility in the Warehouse and Administrative areas of the island (CKY <br />Incorporated 2002). <br />All of the stormwater collected on RRI’s drainage channel system is conveyed to the stormwater <br />pump house area prior to discharge into the Burns Cutoff. Due to the potential migration of PFAS- <br />contaminated groundwater from Site 3 into the drainage channels, and potential accumulation of <br />PFAS-impacted sediment in the vicinity of the stormwater pump house, the PA recommended <br />sediment sampling within the drainage channel adjacent to the stormwater pump house. <br />2.5 Conceptual Site Model <br />Historical operations at NCTS Stockton including the use of AFFF, a material known to contain <br />PFAS, in firefighting, firefighting training, and fire suppression systems have resulted in known <br />or potential PFAS contamination in soil, groundwater, and/or sediment at six AOCs. As outlined <br />in this report, a site inspection is required to obtain PFAS data at each AOC. <br />2.5.1 Contaminant Source Area <br />During the PA, six AOCs were identified as potential areas where the Navy used, stored, or <br />released PFAS-containing materials or AFFF. PFAS has been detected in groundwater at one of