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. Updated Corrective Action Plan—Tosco(76)Service Station No 11192, Stockton, California
<br /> June 26,2002
<br /> 22 Previous Environmental Work
<br /> Based on information supplied by BP and Tosco,the previous USTs(three 10,000-gallon and four 2,000-
<br /> gallon)were installed in 1976, and were removed in 1991 Also in 1991,the three current 10,000-gallon
<br /> gasoline USTs were Installed A soil gas survey was performed in 1989 A well survey was performed in
<br /> 1989 that indicated a water supply well is located 1,100 feet northwest from the site,and a private well is
<br /> located 900 feet from the site Seven groundwater monitoring wells and two vapor extraction wells were
<br /> installed at the site between 1990 and 1991 A hydropunch study, including a soil vapor extraction test,
<br /> was conducted in 1992 Four soil borings were advanced in 1994
<br /> Eight weekly groundwater extraction events occurred between November 16, 2000 and January 2, 2001
<br /> During these events,approximately 2,400 to 3,800 gallons of groundwater per event were removed from
<br /> monitoring well MW-3 by Onyx Industrial Services (Onyx) of Benicia, California In addition,
<br /> approximately 600 gallons of groundwater were removed from well MW-7 on November 16,2000 The
<br /> groundwater was extracted directly from the wells into an Onyx vacuum truck and transported to the
<br /> Tosco Refinery in Rodeo, California, for disposal A total of approximately 27,200 gallons of
<br /> groundwater were removed from the site during the eight weekly extraction events
<br /> Groundwater samples were collected from well MW-3 prior to and following each of the eight
<br /> extraction events A water sample was also collected from the purged groundwater during each of the
<br /> eight events, prior to removal of the water from the site The estimated mass of methyl tertiary butyl
<br /> ether (MtBE) removed with the extracted groundwater was calculated using the average MtBE
<br /> concentration from the pre-purging(MW-3-PRE) and post-purging(MW-3-POST)grab groundwater
<br /> samples for each purging event Based on these average concentrations, an estimated total of 26 63
<br /> pounds of MtBE was removed from the site during the eight purging events between November 16,
<br /> 2000 and January 2, 2001 The weekly purging was discontinued after the eight week period by"" -
<br /> approval from the PHS-EHD
<br /> In April of 2001, GR conducted a subsurface investigation at the site involving eight geoprobe soil
<br /> borings (six offsite and two onsite) and two onsite Cone Penetrometer Tests (CPT) Selected soil
<br /> samples collected during probing and CPT were reported by the laboratory as not detected (ND) for
<br /> Total Petroleum Hydrocarbons as gasoline(TPHg),benzene, toluene, ethylbenzene,xylenes(BTEX),
<br /> MTBE,ethanol,tert-butyl alcohol(TBA), di-isopropyl ether(DIPE),ethyl tert-butyl ether(ETBE), 1,2-
<br /> dichloroethane (1,2 DCA) tert-amyl methyl ether (TAME) and ethylene dibromide (EDB)
<br /> Groundwater samples from the Geoprobes and CPT were reported as ND for all analytes in samples B-
<br /> 3, B-5, B-6, B-7 and B-8 Sample B-1 contained MtBE at 90 ppb and DIPE at 2 8 ppb Sample B-2
<br /> contained only MtBE at 15 ppb Sample B-4 contained MtBE at 11 ppb Sample CPT-1 contained
<br /> MTBE at 120 ppb and 1,2 DCA at 23 ppb
<br /> Also in April of 2001,GR conducted a well search and Sensitive Receptor Survey (SRS)in the vicinity
<br /> of the subject site The well search was conducted within a'/2-mile radius around the site Based on the
<br /> available data supplied by the California Department of Water Resources(DWR),three municipal wells
<br /> • were identified within the 1/2-mile radius of the study area, the closest well is located approximately
<br /> 140245 08 2
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