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i I PROBLEM ASSESSMENT REPORT 1605 South EI Dorado Street Stockton CN4fornta • On July 2 and 3, 1991 Aegis installed monitoring wells MW-1 , MW-2, and MW-3 (Figure 2) Results of the investigation were reported by Aegis to Exxon in a "Phase I Subsurface Investigation Results Report," dated September 13, 1991 Table 2 summarizes TPH and BTEX analytical results from soil sampling Soil boring logs and well construction details are included as Appendix B • On June 10, 1992, Aegis personnel observed and documented the condition and removal of three 10,000-gallon UST, and associated piping Tank removal and sampling were reported by Aegis to Exxon in an "Underground Storage Tank Closure Report," dated October 29, 1992 Table 3 summarizes TPH and BTEX analytical results from soil sampling Figure 3 shows the sample locations With concurrence from SJCPHSIEHD, soil removed during excavation activities was stockpiled on site and replaced in the excavation in March 1993 i • On February 3, 1993, Aegis submitted to Exxon an "Additional Subsurface Investigation Workplan," proposing on and off site monitoring wells to define the extent of petroleum hydrocarbons in groundwater, two vapor extraction wells within the former tank basin to prepare for possible future remediation, and a vapor extraction test from the wells to evaluate the feasibility of this remediation option 2 3 Adjacent Land Uses ' The former Exxon site is bound on the north by 2nd Street and residences, on the east by South EI Dorado Street and a United States Post office, on the south by a car I wash, on the west by Center Street and Valley Lumber yard, and on the northwest by Edison High School (Figure 2) 2 4 Utility Locations Underground utilities present beneath the site include electrical lines to supply the former convenience store, street, and sign lighting, water lines to supply the store and for landscape irrigation, and a sewer Ione for the store bathrooms Aboveground utilities include overhead telephone and electrical power Imes I2 5 Generalized Geology and Hydrogeollogy The site is located within California's Central Valley, a geomorphic province which ,s a relatively flat alluvial plain approximately 450 miles long and 50 miles wide The Central Valley trends northwest and is a large asymmetrical structural trough containing a thick sequence of sediments ranging in age from Jurassic to Recent with ti the greatest depth of sediments in the western section The site Ices within the central I` 91 044A PAR 4