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Site History 14000 Highway 88, Lockeford, CA Time Oil Property No 04-049 3 Additional borings would be placed within the area of contamination and completed as vapor extraction wells for use in a future remediation system The wells would be installed to a minimum depth of 40 feet or to 10 feet below the last observable contamination Authorization to proceed with the proposed work was received from the PHS/EHD on August 4, 1992 Site Assessment - August 1992 Based on the analytical results of the soil samples collected during the tank removal, a site assessment was initiated to determine the extent of hydrocarbon- impacted soils at the subject site On August 26, 1992, a soil vapor survey was performed to assist in determining the extent of impacted soils A pneumatic hammer was utilized to drive 13 soil vapor probes to depths of up to 13 feet in the vicinity of the former tanks Vacuum pumps and charcoal tubes were used to collect vapor samples from each probe at various depths Immediately after collection, each sample was submitted to an onsite mobile lab where it was extracted and infected into a gas chromatograph Due to the presence of hardpan ,just below the ground surface, the results of the soil vapor survey were limited, as no probes could be advanced deeper than 13 feet The survey verified the presence of contamination within the former tank bed and suggested that the hardpan layer had not been affected During the week of September 28, a drill rig was utilized to advance 4 soil borings and install 3 vapor extraction wells and 3 vapor inlet wells During field activities, soils were found to consist of hardpan to approximately 15 feet, this strata was underlain by loose fine to medium sands Dense silty sands and sandy silts were generally encountered at depths of 30 to 35 feet to the extent of the borings Groundwater was not encountered during field activities Drilling at each location was continued until hydrocarbons were no longer indicated by field instrumentation Accordingly, borings SB1, SB3, and SB4 were terminated at a depth of 40 feet while SB2 (WI) was advanced to 45 feet Wells W3, W5, and W6 were installed to 40 feet, while W4 was installed to 30 feet and W2 was installed to 45 feet Wells W1, W2, W3 were installed as 4" diameter vapor extraction wells, and wells W4, W5, and W6 were installed as 2" diameter vapor inlet wells Although each well was constructed using 0 020 slotted casing, screened intervals varied depending on well depth and field observations Three soil samples from each boring were submitted for analysis based on field screening and visual observation (Only 2 samples were submitted from W3 ) Each of the selected samples was analyzed for TPH, BTEX, and ethylene dibromide Results indicated that soil contamination was generally limited to the area of the former tanks and appeared to exist at a depth of 30 feet to 35 feet The highest concentrations of contaminants were indicated in 30-foot samples collected from W1 (SB2) , W2, and SB3 Samples collected from a depth of 15 feet in SBl and W3 contained 200 - 300 ppm gasoline, however, samples collected at 30 feet contained less than 10 ppm gasoline Samples collected from SB4, W4, W5, I 2