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Chevron Products Company 3 Chevron Service Station 9-0557 [ 9 South Center Street Stockton CA March 212001 In November and December 1995, GTT drilled three borings (SB-6, SB-7, SB-9), installed one monitoring well (MW-7), and obtained groundwater grab samples from borings MW-7 and SB-9 to further define the extent of hydrocarbons in soil and groundwater(GTI, January 25, 1996). GTI reported maximum concentrations of TPHg and benzene (640 mglkg and 1.4 mg/kg, respectively) in a soil sample from soil boring SB-9 at 40-1/2 feet bgs. Results of groundwater grab sampling indicated 1,900,000 ppb TPHg in MW-7 and 260,000 ppb in boring SB-9. Benzene was reported as non- detectable in both groundwater grab samples. In October 1997, PACIFIC installed two wells (MW-8 and MW-9) to define the extent of gasoline hydrocarbons in groundwater downgradient of the site and vertically adjacent to the former UST complex. PACIFIC reported maximum concentrations of TPHg and benzene (6,200 ppm and 110 ppm, respectively) in a soil sample from 35 feet bgs in well MW-9. Maximum reported concentrations of TPHg and benzene in soil from 65 to 75 feet bgs in well MW-9 were 8.1 ppm and 0.063 ppm, respectively. Soil results from well MW-8 reported non-detect TPHg and BTEX concentrations. Initial groundwater samples were collected from well MW-8 and MW-9 on October 6, 1997. Concentrations of TPHg and benzene in well MW-8 were reported at 370 ppb and 19 ppb, respectively. Concentrations of TPHg and benzene in well MW-9 were reported at 130,000 ppb and 20,000 ppb, respectively. MtBE was not detected. . A summary of historical soil and groundwater data is included in Attachment A. QUARTERLY MONITORING Quarterly monitoring has been ongoing at the site since March 1991. Historical groundwater gradient has been generally consistent to the south-southeast. Water levels have fluctuated in the wells from approximately 27 feet bgs recently to 47 feet bgs in 1992. Generally, groundwater levels have risen at the site since 1994. Hydrocarbon concentrations in well MW-1, MW-6, and MW-8 located west and downgradient of the former USTs, have declined significantly over time, and are now low to non-detectable. Hydrocarbon concentrations in well MW-5, southeast of the site, have been relatively consistent over time. The highest concentrations of hydrocarbons in groundwater were recently reported in well MW-7, southeast (downgradient) of the site, in which TPHg and benzene were reported at 6,300 ppb and 260 ppb, respectively. SCOPE OF WORK The scope of work included the advancement of four direct push borings by cone penetrometer testing (CPT), and four additional borings immediately adjacent to the CPT borings for the sole purpose of collecting discrete water samples (Figure 2). Discrete groundwater samples were taken to further evaluate the lateral and vertical extent of hydrocarbons, including MtBE, in groundwater. Per approval by Mr. Ron Rowe of the San Joaquin County Public Health Services, soil sampling was abandoned 1AChevron1905571REP0RTS\MtBE Eval1MtBE eval.doc