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Site History <br /> 14000 Highway 88, Lockeford,CA <br /> Time Oil Property No.04049 <br /> 1. Advancing 4 borings to a depth of 40 feet (or to 10 feet past any indications of contamination). <br /> 2. Collecting soil samples from each boring at 5-foot intervals and submitting them for analyses <br /> based on visual observation and field instrumentation readings. <br /> 3. Installing two 2-inch diameter vapor extraction inlet wells use in a future remediation system. <br /> Authorization to proceed with the assessment was received from the PHS/EHD on November 26, 1993. <br /> Additional Soil Investigation - December 1993 <br /> On December 2 and 3, 1993, a mobile drill rig was used to advance three soil borings and install two <br /> vapor extraction wells in the vicinity of the former tank system. During field activities, sails were found to <br /> consist of fine silty sands, sandy silts, or clayey silts to approximately 15 feet below ground surface; this <br /> strata was underlain by fine to coarse sands to a depth of approximately 30 feet. Clayey silt was <br /> generally encountered at 30 feet to 35 feet, while fine to coarse sands were encountered from 35 feet to <br /> the extent of the borings. Groundwater was not encountered during field activities. <br /> Barings SB-6 and SB-7 were advanced to a depth of 41.5 feet below ground surface, while SB-9 was <br /> advanced to 56.5 feet. Wells W-7 and W-8 were installed to a total depth of 56.6 feet, and constructed <br /> with 2-inch diameter PVC casing and 0.020 inch slotted well screen. Both wells were screened from a <br /> depth of 25 feet below ground surface to the extent of the wells. <br /> Based on visual inspection and field instrumentation, 3 to 4 soil samples from each boring were <br /> submitted to a laboratory and analyzed for TPH-g and BTEX. One sample from each boring was also <br /> analyzed for total lead and EDB. None of the soil samples were found to contain detectable <br /> concentrations of TPH-g, with the exception of those collected from W-8 (7,900 ppm at 20 feet; 1,400 <br /> ppm at 45 feet; and 1,700 ppm at 55 feet). Toluene (up to 120 ppm), ethylbenzene (up to 110 ppm), and <br /> xylenes (up to 700 ppm) were also present in the samples collected from W-8. Residual concentrations <br /> of BTEX and total lead were present in several samples collected from SB-7, W-7(SB-8), and SB-9; <br /> however, these did not appear to be present at concentrations of concern. EDB was not indicated in any <br /> of the samples. <br /> A copy of SECOR's"Environmental Site Assessment Report" dated June 14, 1994, was forwarded to the <br /> appropriate regulatory agencies on June 22, 1994. in their reply dated July 7, 1994, the PHSIEHD <br /> agreed with the conclusions of the report and requested that a workplan for the installation of additional <br /> soil borings and/or vapor extraction wells be submitted. <br /> Workplan for Additional Soil Investigation - August 1994 <br /> Based on the data collected during previous investigations, it appeared that the lateral extent of <br /> hydrocarbon-impacted soil had been defined to the northwest (by W-5 and SB-6), west (by SB-4), <br /> southwest (by SB-7 and W-7), south (by W-6), and east (by SB-9) of the former tank system. However, <br /> it was not defined to the north and northeast. On August 30, 1994, SECOR's "Workplan for Additional <br /> Environmental Investigation" was forwarded to the appropriate regulatory agencies. The workplan <br /> proposed these activities: <br /> 1. Three borings would be advanced to a depth of 65 feet (or to 10 feet past any indications of <br /> contamination). <br /> 3 <br />