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Chevron Products Company 2 Chevron Service 5tadon 9-0557. 139 Soath Center Street.Stockton,CA March 21-2001 . from the site and replaced with three 10,000-gallon capacity and one 1,000-gallon capacity double-walled fiberglass USTs. The former USTs consisted of two 10,000- gallon gasoline, one 5,000-gallon unleaded gasoline, and one 1,000-gallon used oil tank. With oversight from Ms. Casey Folley of the San Joaquin County Environmental Health Department, GTI collected soil samples from the UST pits and product line trenches. GTI reported concentrations of hydrocarbons over 50 parts per million (ppm) present in samples collected from the UST pit, used oil tank pit, and southern end of the eastern product island. GTI oversaw subsequent over-excavation in these areas and reported hydrocarbon concentrations less than 50 ppm in samples collected from the bases of the over-excavated areas (GTI, April 23, 1990). In February 1991, GTI drilled four borings at the site and installed wells MWA through MW-4 in the borings (GTI, April 5, 1991). Soils encountered consisted of clayey silt, silty to sandy clay, and lenses of gravelly sand to the depth explored of 60 feet below ground surface (bgs). No detectable concentrations of hydrocarbons were reported in the soil samples collected from these borings. Groundwater was reported at a depth of approximately 45 feet bgs, and the direction of groundwater flow was reported to the southeast. Total petroleum hydrocarbons calculated as gasoline (TPHg) and benzene were reported in groundwater samples collected from wells MW-1 and MW-2 at concentrations of 1,400 parts per billion (ppb) and 250 ppb, and 290 and 140 ppb, respectively. Non-detectable concentrations of TPHg and benzene were reported in wells MW-3 and MW-4. In November 1992, GTI installed well MW-5 offsite to further define the extent of gasoline hydrocarbons in groundwater southeast (downgradient) of the site (GTI, January 25, 1993). Three soil samples collected from the boring were reported to contain non-detectable concentrations of hydrocarbons. Groundwater samples from well MW-5 were reported to contain non-detectable concentrations of hydrocarbons. In September 1993, GTI installed well MW-6 offsite to further define the extent of gasoline hydrocarbons in groundwater west of the former USTs at the site (GTT, January 28, 1994). Seven soil samples collected from the boring were reported to contain non-detectable concentrations of TPHg and benzene; very low (0.012 ppm to 0.022 ppm) concentrations of toluene and xylenes were reported in 2 of the 7 samples. Groundwater samples from well MW-6 were reported to contain 980 ppb TPHg and 9 ppb benzene. In May 1994, GTI drilled five borings (SB-1 through SB-5) onsite to further define the extent of hydrocarbons in soil in the areas of the eastern pump island, former USTs, and former used oil UST (GTI, June 28, 1994). Thirty-seven soil samples collected from the borings were analyzed. The maximum concentrations of TPHg and benzene (15,000 ppm and 160 ppm, respectively) were reported in a sample from boring SB-4, in the former UST pit. Groundwater was reported at a depth of 43 feet bgs. lil IAChevron1905571REPORTS\MtBE EvaAMtBE eval.doc