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Site History 14000 Highway 88, Lockeford, CA :-J Time Oil Property No.04-049 1. Advancing 4 borings to a depth of 40 feet (or to 10 feet past any indications of contamination). 2. Collecting soil samples from each boring at 5-foot intervals and submitting them for analyses based on visual observation and field instrumentation readings. 3. Installing two 2-inch diameter vapor extraction inlet wells use in a future remediation system. Authorization to proceed with the assessment was received from the PHS/EHD on November 26, 1993. Additional Soil Investigation - December 1993 On December 2 and 3, 1993, a mobile drill rig was used to advance three soil borings and install two vapor extraction wells in the vicinity of the former tank system. During field activities, soils were found to consist of fine silly sands, sandy silts, or clayey silts to approximately 15 feet below ground surface; this strata was underlain by fine to coarse sands to a depth of approximately 30 feet. Clayey silt was generally encountered at 30 feet to 35 feet, while fine to coarse sands were encountered from 35 feet to the extent of the borings. Groundwater was not encountered during field activities. Borings SB-6 and SB-7 were advanced to a depth of 41.5 feet below ground surface, while SB-9 was advanced to 56.5 feet. Wells W-7 and W-8 were installed to a total depth of 56.6 feet, and constructed with 2-inch diameter PVC casing and 0.020 inch slotted well screen. Both wells were screened from a depth of 25 feet below ground surface to the extent of the wells. -; Based on visual inspection and field instrumentation, 3 to 4 soil samples from each boring were submitted to a laboratory and analyzed for TPH-g and BTEX. One sample from each boring was also analyzed for total lead and EDB. None of the soil samples were found to contain detectable concentrations of TPH-g, with the exception of those Collected from W-8 (7,900 ppm at 20 feet; 1,400 ppm at 45 feet; and 1,700 ppm at 55 feet). Toluene (up to 120 ppm), ethylbenzene (up to 110 ppm), and xylenes (up to 700 ppm) were also present in the samples collected from W-8. Residual concentrations of BTEX and total lead were present in several samples collected from SB-7, W-7(SB-8), and SB-9; however, these did not appear to be present at concentrations of concern. EDB was not indicated in any of the samples. A copy of SECOR's "Environmental Site Assessment Report" dated June 14, 1994, was forwarded to the appropriate regulatory agencies on June 22, 1994. In their reply dated July 7, 1994, the PHS/EHD agreed with the conclusions of the report and requested that a workplan for the installation of additional soil borings and/or vapor extraction wells be submitted. Workplan for Additional Soil Investigation - August 1994 Based on the data collected during previous investigations, it appeared that the lateral extent of hydrocarbon-impacted soil had been defined to the northwest (by W-5 and SB-6), west (by SB-4), southwest (by SB-7 and W-7), south (by W-6), and east (by SB-9) of the former tank system. However, it was not defined to the north and northeast. On August 30, 1994, SECOR's "Workplan for Additional Environmental Investigation" was forwarded to the appropriate regulatory agencies. The workplan proposed these activities: 1. Three borings would be advanced to a depth of 65 feet (or to 10 feet past any indications of contamination). 3