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N"111 sftavo� Semi-Annual Groundwater Monitoring and Quarterly Remediation Progress Report—First Quarter 2013 April 30,2013 Project#52.75118.2390 Page 1 1.0 SITE INFORMATION AND BACKGROUND Introduction The site is currently an operating 76-branded gasoline service station located at 1403 West Country Club Boulevard in Stockton, California (Figure 1). The operating facility consists of a station building, a car wash, an auto service bay, an oil change building, four dispenser islands, a canopy, three 10,000-gallon gasoline (double-walled) underground storage tanks (USTs), one 2,500-gallon waste oil UST (operated by others), and associated product lines (Figure 2). Properties in the site vicinity are primarily residential and commercial developments. A former Shell Service Station was located across Pershing Avenue, east of the site (1267 Country Club Boulevard). Background The site was operated as a gasoline service station by Mobil Oil Company, following the installation of two 10,000-gallon unleaded gasoline USTs, one 10,000-gallon leaded gasoline UST, three 3,000-gallon motor oil USTs, and one 3,000-gallon waste oil UST, associated piping and dispensers, and other facility structures in 1976. The site was purchased by British Petroleum (BP) in May 1989. The site was operated under BP ownership until Tosco Corporation (now ConocoPhillips) assumed operations in 1994. Prior to first quarter 2010, 'shallow' and 'deep'were used to identify the groundwater monitoring zones for wells screened to depths ranging from 8 feet (ft) to 45 ft below ground surface (bgs) (MW-1 through MW-10, MW-12, and MWA 3) and 68.5 ft to 78.5 ft bgs (MW-11), respectively. However, it was determined the dissolved plume and regional hydraulic gradients may be better evaluated with additional water-bearing zones. Beginning 1Q10, 'shallow' and 'deep' are no longer used to describe the groundwater monitoring zones. Instead A-Zone (screened between 8 ft and 30 ft bgs), B-Zone (screened between 20 ft and 45 ft bgs), and C-Zone (screened between 58 ft and 78.5 ft bgs) are used to describe the regional water-bearing zones. This corresponds with water-bearing zones identified at the adjacent former Shell Station. A site location map and a detailed site plan are included as Figures 1 and 2, respectively. An extended site plan is included as Figure 3. The current and historical groundwater monitoring and analytical data are summarized in Tables 1 and 2 and are presented on Figures 4 through 15. The current and historical groundwater flow direction and hydraulic gradient data are summarized in Tables 3 through 5. Well construction details are found in Table 6. Previous investigations and site history and are summarized in Appendix A. Groundwater monitoring and sampling field data sheets are included as Appendix B. A certified laboratory analytical report and chain-of-custody documentation are included as Appendix C. Groundwater monitoring data tables for the Former Shell Service Station located at 1267 Country Club Lane are included as Appendix D. Current Site Information Current phase of project: Groundwater monitoring, sampling, and remediation Semiannually(first and third quarters): MW-3, MW-7, and MWA 1; annually(first quarter): Frequency of monitoring and sampling: MW-6 and MWA 2; biennially(first quarter of odd-numbered years): MWA, MW-4, MW-5, MW-8 through MWA 0, and MWA 3 Have separate-phase hydrocarbons (SPH) No historically been found on-site?