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. Well Installation Report - Former Unocal Service Station No 0187 October 21, 1997 GSI performed a limited environmental site assessment (ESA) of the properties in the vicinity of the subject site The ESA identified a former station located at 448 East Miner Avenue, south of the subject site. Historical groundwater data indicates that this former station is upgradient of the subject site. Environmental information related to the soil and groundwater conditions beneath this former service station were not obtained during the ESA. Environmental data related to surrounding properties in the vicinity of the subject site are discussed in GSI Report No 4827 04-1, Limited Phase I Environmental Site Assessment, dated May 11, 1995. i To further assess on-site and off-site subsurface conditions, GSI installed three additional on-site groundwater monitoring wells (U-4 through U-6) and two off-site groundwater monitoring wells (U-7 and U-8), drilled two additional on-site exploratory soil borings (U-N and U-O), and installed one on-site vapor extraction well (UV-1) in August 1995 TPHg or benzene were not detected in soil samples collected from borings U-5 through U-7 or U-O TPHg was detected in the soil sample collected from boring U-N at 25 feet bgs (1 7 ppm) TPHg and benzene were detected in the soil sample collected from well boring U-4 at 10 feet bgs (41 and 0 011 ppm, respectively) TPHg was detected in the three soil samples collected from well boring UV-1 at 25, 35, and 40 feet bgs at • concentrations ranging from 3,400 to 20,000 ppm. Benzene was detected in the soil samples collected at 35 feet (99 ppm) and 40 feet bgs (15 ppm) in UVA Quarterly monitoring and sampling of the groundwater monitoring wells began in August 1994. Dissolved concentrations of TPHg and benzene have been detected in wells U-1 through U-4, U-7, and U-8 The groundwater flow direction has been to the northeast Historical analytical data indicate that dissolved hydrocarbons are undefined to the northeast of wells U-3 and U-4 FIELD ACTIVITIES Field work was performed in accordance with the GSI Site Safety Plan #4827 21, dated August 15, 1997 GST Field Methods and Procedures are included in Appendix A Underground Service Alert (USA) was notified prior to beginning drilling activities Drilling and well installation was performed under SJCEHD permit #13207 dated July 30, 1997, and City of Stockton encroachment permit #64353. Copies of the well installation and encroachment permits are presented in Appendix B. One off-site groundwater monitoring well (U-9) was installed on August 19, 1997 The boring was drilled using a truck-mounted drill rig equipped with 8-inch-diameter hollow-stem augers Drilling was performed by Woodward Drilling Company (C57 #710079) A GSI geologist observed the drilling of the boring, described the encountered • 482721-2 3