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SiteHisto Jackpot Food po acod ilAart, 1434 W Yosemite Ave,Manteca,CA Time all Property No 04167 The results of the survey suggested that Impacted soils were limited to the area of the north pump Island and did not extend laterally to any great degree A copy of the Canonie's "Soil Vapor Survey Report with Proposed Boring and Well Locations"was forwarded to the PHS/EHD and CRWQCB on September 24, 1992 During the week of October 5, 1992, a drill rig was utilized to install 4 groundwater monitoring wells and 3 vadose zone vapor extraction wells in the vicinity of the former tanks During field activities, soils were found to consist of loose fine to medium sands to a depth of approximately 15 feet This strata was underlain by a 1-foot to 4-foot thick layer of stiff silty clay which appeared to act as an aquitard (15 to 19 feet below ground surface) Just below the clay unit, saturated sands/silty sands were encountered, while moist silty clays were encountered at 30 feet Wells W1, W2, and W4 were constructed as vadose zone extraction wells Each of these wells was installed to a depth 15 feet and screened from a depth of 5 feet to the extent of the well with 4-inch diameter, 0 020-inch slotted well screen Because it was thought that the first clay unit represented a possible aquitard, monitoring wells W3, W5, W6, and W7 were constructed to insure that contamination to the groundwater did not occur through the creation of a vertical conduit Accordingly, W5, W6, and W7 were completed as 30-foot monitoring wells, screened from a depth of 20 feet to the extent of the well with 2-inch diameter 0 020-inch slotted casing Due to its potential for use in a pumping system, W3 was constructed with 4-inch diameter casing and screened similarly to the 2-inch wells Two to three soil samples from each boring were transported to an analytical laboratory and analyzed for TPH, BTEX, and ethylene dibromide Gasoline and xylenes were present at 100 ppm and 2 ppm, respectively, in the sample collected from W2 at a depth of 5 feet, however, no contaminants were detected at a depth of 15 feet Samples collected from W4 at a depths of 5 feet and 10 feet contained 26 ppm and 290 ppm gasoline, as well as ethylbenzene and xylenes However, soil samples collected from W3 (installed adjacent to W4) contained only 0 71 ppm gasoline and trace BTEX constituents at a depth of 14 feet, while no contaminants were found at 20 feet None of the other samples contained detectable concentrations of gasoline or BTEX On November 5, the groundwater wells were developed and sampled Prior to purging, an east- southeasterly gradient was determined by measuring the depth to groundwater in each well The sample collected from W3 was found to contain 0 55 ppb xylenes, however, no contaminants were detected in the remaining samples After the installation of the wells, a vapor extraction pilot test was performed on W1, W2, and W4 to evaluate the feasibility of in-situ remediation by vapor extraction The results of the study indicated that soil vapors can be easily extracted from the existing wells and that this technology appears appropriate for site remediation Based on the results of the site assessment and previous investigations, it appears that the extent of gasoline-impacted soil is well defined and remains limited to the area of the pump islands Although trace concentrations of xylenes were present in the groundwater sample collected from W4, the levels indicated were far below California's primary drinking water quality standards (1750 ppb for xylenes) A copy of Canonie Environmental's "Site Assessment Report" was forwarded to the PHS/EHD and CRWQCB on May 26, 1993 In their reply dated June 24, 1994, the PHS/EHD requested that additional borings be placed to determine the extent of hydrocarbon-impacted soils and that the groundwater monitoring wells on the subject site be re-sampled 2