SITE INFORMATION AND CORRESPONDENCE

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NARRATIVE WORK DESCRIPTION FOR SUBSURFACE INVESTIGATION 117 WEST HARDING WAY STOCKTON, CALIFORNIA In March 1990, one 1,000-gallon UST and all associated piping and dispensing equipment were removed and transported off-site. Laboratory analysis of soil samples collected from beneath the former 1,000-gallon UST location indicated the presence of detectable concentrations of ethylbenzene and xylenes. After the tank was removed, the area of excavation of the former tank was backfilled. On November 26, 1997, ATC Associates Inc. submitted a workplan for a subsurface investigation at the site. The workplan was submitted at the request of the San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) and PHS/EHD approved the workplan with minor modifications. On January 8, 1998, an ATC geologist supervised the advancement of one soil boring to 41.5 feet below ground surface (bgs). A site plan showing the location of soil boring SB I is included as Figure 2. Soil samples were collected at five foot intervals and submitted for analysis of total petroleum hydrocarbons as gasoline and diesel (TPHg and TPHd) by EPA Method 8015; and volatile organic compounds (VOCs) by EPA Method 8260. A Hydropunch groundwater sampling probe was advanced in the soil boring and a groundwater sample was collected. The groundwater sample was analyzed for TPHg, TPHd, VOCs, and halogenated volatile organic compounds (HVOCs) by EPA Method 8010/8020. Subsequent to the sample collection, the open sampling hole was tremie grouted to the surface with neat cement. Petroleum hydrocarbon constituents were detected in soil samples collected from boring SB I. The highest reported constituent concentrations were observed in the soil sample collected at 5.5 feet bgs. The petroleum hydrocarbons appeared to attenuate rapidly with depth as indicated greatest by soil sample from 35.5 feet bgs, which contained only trace levels of isopropyibenzene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. Trace amounts of petroleum hydrocarbon constituents were also detected in the groundwater sample collected from soil boring SB 1. On June 5, 1998, ATC Associates Inc. submitted a Workplan for Soil Excavation and Additional Subsurface Investigation at the site. At the request of PHS/EHD, ATC submitted a revised workplan on July 8, 1998. The workplan was submitted at the request of the PHS/EHD and PHS/EHD approved the workplan with minor modifications. On September 13, 1998, ATC personnel supervised the excavation of the impacted backfill material, approximately 85 tons, located in the former UST location. The excavated backfill material was immediately transported to Forward Inc. landfill in Stockton. Confirmation soil samples were collected from the excavation sidewall and bottom and analyzed for TPHg, TPHd,