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Former Unocal Service Station 1!0187 October 9, 1995 detected in these soil samples Results of this subsurface investigation are presented in GSI Report No. 782702-3, Exploratory Soil Boring Report, dated December 15, 1992 In July 1994, GSI drilled five additional onsite soil borings (U-I through U-M) and installed three onsite groundwater monitoring wells (U-1 through U-3) TPHg were detected in soil samples analyzed from borings U-J (1 7 ppm at 26 5 feet bgs) and U-K (130 ppm at 41 5 feet bgs) TPHg were detected in soil samples analyzed from borings U-3 (330 ppm at 46 5 feet bgs), U-L (19,000 ppm at 45 5 feet bgs), and U-M (510 ppm at 45 5 feet bgs) Results of this subsurface investigation are presented in GSI Report No 4827 703-5, Well Installation and Exploratory Soil Boring Report, dated September 21, 1994. I 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 iAssessment, dated May 11, 1995 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-3, with the highest concentrations occurring in well U-3 (42,000 and 9,600 parts per billion, or ppb, respectively) Quarterly sampling and monitoring of the wells is performed by MPDS Inc of Concord, California Data from the most recent sampling event (August 9, 1995) was reported in MPDS Report No MPDS-UN0187-04, Quartet ly Data Report, dated August 25, 1995 FIELD ACTIVITIES Field work was performed in accordance with the GSI Site Safety Plan #4827 04, dated February 14, 1995 GSI Field Methods and Procedures are included in Appendix A Underground Service Alert (USA) was notified prior to beginning drilling activities Subtronics Corp of Concord, California, was contracted to clear underground utilities in the vicinity of the proposed boring and well locations Drilling and well installation was performed under SJCEHD permit numbers 006661 and 006662 dated July 17, 1995. Encroachment permit number 63503 was obtained from the City of Stockton for the off-site monitoring wells Copy of the well installation and encroachment permits are presented in Appendix B 4827 04-3 3 w