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Map ID MAP FINDINGS Direction Distance EOR ID Number Elevation Site Database(s) EPA ID Number TRACY DEFENSE DEPOT(USARMY) (Continued) 1000182407 is more than half full.During the summer,the water in the pond percolates or evaporates,and the pond dried up completely.The pond sediment has been scraped at least once in the past 20 years. Site characterization investigations at the SWMU 4,which began with the comprehensive Remedial Investigation/Feasibility Study(RI/FS),were completed in 2001.The ROD includes a selected remedy for SWMU 4,but also identified areas of uncertainty (data gaps).Subsequent investigations to address those data gaps resulted in the development of a(BERA). SWMU 6 Solid Waste Management Unit(SWMU)6 is the site of a former 250-gallon concrete sump built sometime after the completion of Building 28 in 1968.This building was once used to repackage materials with damaged containers,and the residual waste was emptied into the sump.Waste was then pumped into 55-gallon drums and removed to a Class I disposal site.In 1977,the sump was abandoned in place and filled with sand. The sump was removed in 1988.During the remedial investigation,pesticide and herbicide contamination was detected in soil samples collected from between the former sump and the water table. Excavation activities at SWMU 6 began on 22 June 1999 within the proposed excavation footprint It feet by 15 feet) described in the ROD.The base of the initial excavation was 18 feet,as required by the ROD.Following the completion of the initial excavation,six initial soil samples were collected,including one from each of the four excavation sidewalls and two from the excavation bottom. SWMU 7 SWMU 7 consists of seven pits that were reportedly operated before the construction of the warehouse and buildings currently at the site.The pits were used for disposal of medical supplies,narcotics,general pharmaceuticals,and electron tubes.The pits may have been up to 16 feet deep;ashes were removed and transported to off-site landfills during the later years of operation. SWMU 8 SWMU 8 is the former location of a single large bum pit near the eastern extent of DDJC-Tracy.SWMU 8 is referred to as Bum Pit No.2.The bum pit was reported to be 250 feet by 30 feet and 16 feet deep.Bum Pit No.2 reportedly operated between 1942 and 1971.Various containers,crates,wooden pallets, trash,and unknown solids,liquids,and narcotics were burned in the pit.The area surrounding SWMU 8 is unpaved and is slightly depressed topographically. The remedy selected in the ROD required the excavation and off-site disposal of approximately 8,000 cubic yards of contaminated soil and debris.The area of the excavation specified was approximately 280 feet by 70 feet,and the soil and debris were to be excavated to approximately 14 feet below ground surface(bgs),or the depth of the water table.Clean soil imported from off site was to be used to backfill the excavation. Mobilization for remedial activities at SWMU 8 occurred on 23 September 2002 with excavation commencing on October 8,2002.Based on the results of a design data collection effort performed at SWMU 8,the area of the excavation was increased from that approximated in the ROD.The excavation footprint was extended approximately 20 feet to the southeast because Chlordane and Dieldrin were detected in a soil sample collected outside of the ROD-specified excavation boundary.The base excavation and initial overexcavation were completed between October 8,2002 and November 14,2002. The depth along the center of the excavation was approximately 20 feet bgs, which was below the seasonal high level for the groundwater table. Initial confirmation sample results from the sidewalls and bases(benches and bottom) of the excavation indicated that additional excavation was needed to remove additional soil with contaminants exceeding the cleanup standards.Fourteen step-out excavations were performed,and confirmation soil samples were collected following the completion of each step-out.Residual contamination following the first stepout necessitated a second round of stepout excavations.Confirmation soil samples collected showed that concentrations of the pesticides DDT and Dieldrin exceeding cleanup standards remain at SWMU 8. Additional excavation was not performed at sample locations with TC3372962.1s Page 39