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SS No. 6348, Tracy <br /> PIER, 1/31/92 <br /> BACKGROUND <br /> The business at the site is a Unocal service station <br /> which has been in operation since 1972 and is scheduled for <br /> closure at the end of March, 1992 . The facilities consist of a <br /> metal and stone building containing an office area and three <br /> service bays, as well as two pump islands and associated <br /> canopy, underground product tanks, an enclosure containing <br /> waste-oil storage drums , an above-ground propane tank, and <br /> storage buildings. Mayor site features and the locations of <br /> all monitoring wells and borings are shown on Figure 2 . <br /> On June 18, 1990 a 550-gallon underground waste-oil <br /> storage tank was removed. According to San Joaquin County <br /> Public Health Service records and a report by Kaprealian <br /> Engineering (9/24/90) , the steel tank was found to have holes <br /> and to have leaked . Following tank removal , an excavation <br /> that measured 9' wide, 12 ' long, and 14 .5' deep was made to <br /> remove oil-contaminated soil. Not all oil-contaminated soil <br /> was removed, due to the proximity of the fuel storage tanks. <br /> • The excavation was backfilled with pea gravel. <br /> Laboratory analysis of soil samples taken from the <br /> base of the over-excavated tank pit indicated 3 . 7 ppm TEPH at <br /> the 14 foot depth, with BTEX not detected. Three sidewall <br /> samples, collected 6 to 12" above the observed water level, had <br /> Total Extractable Hydrocarbon concentrations of 210 ppm (north <br /> wall) , 95 ppm (north side of the east wall) , and 270 ppm (south <br /> side of the east wall) . The four samples were also analyzed <br /> for halogenated volatile organic substances and for <br /> semivolatile organic substances . Kaprellan Engineering <br /> reported that none of these was detected. The samples were <br /> also analyzed for heavy metals, without any unusual results. <br /> A Phase I investigation of records pertaining to the <br /> site and an inspection of the physical property were conducted <br /> by PHR Environmental Consultants, Inc. in June of 1991. PHR <br /> identified areas of potential contamination as follows: pit of <br /> the former underground waste-oil tank; storage tanks, piping, <br /> and pumps of the gasoline supply ; observed spillage at <br /> above-ground waste-oil storage drums; floor-drain/clarifier <br /> system within the service bays ; and off-site sources of <br /> contamination. <br /> -2- <br />