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<br /> Site History
<br /> 14000 Highway 88,Lockeford,CA
<br /> Time Oil Property No 04-049
<br /> Site Assessment-August 1992
<br /> On August 25, 1992, a soil vapor survey was performed to assist in determining the extent of impacted
<br /> soils A pneumatic hammer was used to drive 13 soil vapor probes to depths of up to 13 feet in the
<br /> vicinity of the former tanks Vacuum pumps and charcoal tubes were used to collect vapor samples from
<br /> each probe at various depths Immediately after collection, each sample was submitted to an onsite
<br /> mobile lab where it was extracted and injected into a gas chromatograph Due to the presence of
<br /> hardpan just below the ground surface, the results of the soil vapor survey were limited, as no probes
<br /> could be advanced deeper than 13 feet
<br /> During the week of September 28, a drill rig was used to advance 4 soil borings and install 3 vapor
<br /> extraction wells and 3 vapor inlet wells During field activities, soils were found to consist of hardpan to
<br /> approximately 15 feet, this strata was underlain by loose fine to medium sands Dense silty sands and
<br /> sandy silts were generally encountered at depths of 30 to 35 feet to the extent of the borings
<br /> Groundwater was not encountered during field activities
<br /> Drilling at each location was continued until hydrocarbons were no longer indicated by field
<br /> instrumentation Accordingly, borings S61, SB3, and SB4 were terminated at a depth of 40 feet while
<br /> SB2 (W1) was advanced to 45 feet Wells W3, W5, and W6 were installed to 40 feet, while W4 was
<br /> installed to 30 feet and W2 was installed to 45 feet Wells W1, W2, W3 were installed as 4" diameter
<br /> vapor extraction wells, and wells W4, W5, and W6 were installed as 2 diameter vapor inlet wells
<br /> Although each well was constructed using 0 020 slotted casing, screened intervals vaned depending on
<br /> well depth and field observations
<br /> Three soil samples from each boring were submitted for analysis based on field screening and visual
<br /> observation (Only 2 samples were submitted from W3 ) Each sample was analyzed for TPH, BTEX,
<br /> and ethylene dibromide Results indicated that soil contamination was generally limited to the area of
<br /> the former tanks and appeared to exist at a depth of 30 feet to 35 feet The highest concentrations of
<br /> contaminants were indicated in 30-foot samples collected from W1(SB2), W2, and SB3 Samples
<br /> collected from a depth of 15 feet in SB1 and W3 contained 200 - 300 ppm gasoline, however, samples
<br /> collected at 30 feet contained less than 10 ppm gasoline Samples collected from SB4, W4, W5, and
<br /> W6 contained trace to "non-detect" concentrations of contaminants None of the samples collected from
<br /> depths of 40 feet to 45 feet contained detectable concentrations of gasoline or its constituents
<br /> After the installation of the wells, a vapor extraction pilot test was performed on W1, W2, and W3 to
<br /> evaluate the feasibility of in-situ remediation by vapor extraction The results of the study indicate that
<br /> soil vapors can be easily extracted from the existing wells and that vapor extraction appears to be
<br /> appropriate for site remediation
<br /> Based on the results of the site investigation, it appeared that impacted soils were limited to the former
<br /> tank excavation and the more dense soils encountered at a depth of 30 feet Although several of the soil
<br /> samples submitted for analyses contained trace concentrations of hydrocarbons, SB4, W4, W5, and W6
<br /> generally defined the extent of soil contamination to the west, southwest, north, and south of the tanks
<br /> A copy of Canonie's "Site Assessment Report" was forwarded to the appropriate regulatory agencies on
<br /> May 25, 1993 In their reply dated June 18, 1993, the PHS/EHD requested that a workplan for an
<br /> additional investigation to verify the extent of soil contamination be submitted
<br /> Workplan for Additional Site Activities- October 1993
<br /> A copy of Science and Engineering Analysis Corporation's (SECOR) "Workplan, Additional
<br /> Environmental Investigation" was forwarded to the appropriate regulatory agencies on October 20, 1993
<br /> The goal of the proposed investigation was to completely define the lateral extent of impacted soils at
<br /> the subject site Site assessment activities proposed to meet the project goals included
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