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1.0 INTRODUCTION Conestoga-Rovers&Associates (CRA) prepared this Site Investigation Work Plan (Work Plan) on behalf of Equilon Enterprises dba Shell Oil Company US (Shell) for the Shell- branded service station at 620 West Charter Way, Stockton, California (site). The purpose of this investigation is to delineate the extent of gasoline constituents in Zone B of the site. The proposed scope of work complies with San Joaquin County Environmental Health Department (SJCEHD) and Regional Water Quality Control Board guidelines. The site is an active Shell-branded service station located at 620 West Charter Way, east of Interstate 5 in a commercial area of Stockton, California (Figure 1). The site layout includes a service station building, six dispenser islands, a fuel underground storage tank (UST) complex, and a'car wash (Figure 2). Future use of the site is assumed to be similar to current use. A summary of historical activities at this site is provided in Appendix A. Groundwater at the site consists of thr,ee zones: Zone A (20 to 45 feet below grade {fbg)), Zone B (45 to 50 fbg); and Zone C (65 to 90 fbg). Groundwater in Zone A is monitored by wells MW-1 through MW-11. Groundwater in Zone B is monitored by wells MW-13- " 50, MW-14-50, MW-16-50,-and MW-17-50 at the 45 to 50 fbg interval.' Groundwater in Zone C is monitored by wells MW-13-77,MW-14-77, MW-15-77,and MW-16-77 at the 65 to 77 depth interval and by well MW-16-90 at approximately 90 fbg. - During the preparation of a Corrective Action Plan (CAP) requested by SJCEHD for the site, all of the available site data was evaluated to determine the most appropriate remedial approach. During the review of site data, CRA determined that additional site assessment was warranted in order to fully understand the distribution of gasoline constituents beneath the site in Zone B and prior to selection of an appropriate remedial approach for the site. SJCEHD agreed with this approach and allowed a work plan to be submitted in place of a CAP at this time. Areas of the site requiring additional assessment are summarized below. Separate phase hydrocarbons (SPH) were present in Zone B in monitoring well MW-16-50 during the first, second and fourth quarters of 2009 at thicknesses of 0.05, -r'r 0.11, and 0.05 feet, respectively. In the last analysis of groundwater from MW-16-50 in hos s October 29, 2008,'total petroleum hydrocarbons as gasoline (TPHg) and benzene were detected at concentrations of 65,000 pg/L and 1,100 pg/L, respectively.e TPHg and Std• u-1 benzene were detected at 47 fbg in groundwater from nearby CPT location CPT-4 inA4 March 30, 2000 at concentrations of 439,000 and 13,200 µg/L, respectively. .In order to �r 240778(s) 1 CONESTOGA-ROVERS&ASSOCIATES