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Mr. Ron Rowe September 4, 1997 Page 2 Additional properties in the Site vicinity with former or existing USTs that did not have files available for review at the SJCEHD include: • Tune-Up Masters,West Charter Way • City of Stockton Corporate Yard,South Lincoln Street The depth to first encountered groundwater in the Site vicinity ranges from approximately 35 feet bgs to 43 feet bgs. Groundwater flow is generally to the east; however, it has historically ranged from northeast to southeast. Groundwater quality data collected during 1994 and 1995 indicate that petroleum hydrocarbon releases to groundwater have been confirmed from the Texaco Service Station,Transmission Shop,and the Chevron Service Station. In February 1996,SECOR conducted a soil and groundwater investigation that included the advancement of two soil borings (SB-1 and SB-2), installation of one groundwater monitoring well (MW-1), and one vapor extraction well (VE-1). Results of this investigation indicate that soil underlying the west end of the former USTs between depths of approximately 10 to 40 feet bgs have been impacted with gasoline-range petroleum hydrocarbons. TPHg,benzene,toluene,ethylbenzene,and xylenes (BTEX)were detected at concentrations ranging from 1,400 to 13,000 mg/kg, 11 to 44 mg/kg, 63 to 480 mg/kg, 20 to 180 mg/kg, and 100 to 910 mg/kg,respectively. Analyte concentrations generally decreased with depth. The lateral extent of petroleum hydrocarbon-affected soils within the vadose zone appears to be limited to a 20-foot radius from the approximate point of release. Analytical results for groundwater samples collected from the SB-1,SB-2 and MW-1 locations indicated the presence of TPHg and BTEX beneath the former USTs at maximum concentrations of 190,000 micrograms per liter(ug/1),32,000 ug/l,41,000 ug/1,4,500 ug/l and 23,000 ug/1,respectively. Analytical results obtained for nearby monitoring wells owned by Texaco(MW-6,MW-8,and MW-14)indicated the presence of TPHg, benzene,and xylenes in samples from wells MW-8 and MW-14 at maximum concentrations of 550 ug/l,23 ug/l and 1.1 ug/l, respectively. TPHg and BTEX were not present in the sample from well MW-6 above laboratory reporting limits. Soil beneath the Site can generally be divided into an upper silt and clay-dominated interval extending from the ground surface to approximately 38 to 44 feet bgs and an underlying sand-dominated interval extending to at least 50 feet bgs. The sand-dominated interval appears to represent the primary uppermost groundwater- bearing zone beneath the Site. 2.0 PRELIMINARY FIELD ACTIVITIES Before initiation of field activities, SECOR will update the existing Site-specific Health and Safety Plan (HASP)to address the proposed scope of work and obtain well construction permits from the SJCEHD. The proposed drilling locations will be cleared with respect to underground utilities and other obstructions using a professional utility locator and Underground Service Alert(USA)will be notified at least 48-hour in advance of field activities. SECOR will also conduct a conduit study which will focus on the potential for vertical conduits in the immediate vicinity of the site. This study will include a detailed survey of all wells in the area using HASFFB\STOCKTON\SFFB W KP.RPT