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1.0 INTRODUCTION On behalf of Phillips 66 Company (P66), Cardno ATC is submitting this Monitoring Well Destruction Work Plan (Work Plan) to the California Regional Water Quality Control Board — Central Valley Region (CRWQCB - CVR) for the destruction of 19 monitoring wells, 6 piezometers, and 9 remediation wells at the Former Tosco Bulk Terminal No. 10013 (site). This Work Plan was prepared in response to the Request for Well Destruction letter from the CRWQCB—CVR dated February 27, 2013 (Appendix A). 2.0 SITE LOCATION The site is located at 3505 Navy Drive in Stockton, California as shown on Figure 1. A Site Plan is provided as Figure 2. Land use in the surrounding area can be described as mixed commercial and industrial. The site is currently occupied by a bulk fuel distribution facility. 2.1 Previous Investigations Several phases of investigation have occurred at the site. In April 1987, a 285-gallon vapor knock-out tank (former Tank "A") was replaced with the existing 550-gallon fiberglass knockout tank. During removal, hydrocarbon sheen was noted in the Tank A excavation. In response, monitoring wells MW-1, MW-2 and MW-3 were installed. Groundwater monitoring and sampling was initiated at the site in 1987. Monitoring wells MW-4, MW-5 and MW-6 were installed in February 1989. In February 1993, nine soil borings were installed in the southwest portion of the site and offsite to the west, and three of the onsite borings were completed as monitoring wells MW-7, MW-8, and MW-9. In November 1994, 5 cone penetration test borings were advanced, 26 borings were sampled and four of these borings were completed as monitoring wells MW-10 through MW-13. Well MW-7 was subsequently destroyed in 1996. The GWETS and associated piping were installed in June and July of 2003. Groundwater extraction was terminated on July 31, 2006; the rental portions of the GWETS were dismantled in August 2006. Mobile oxygen injections were started in December 2007, as part of a pilot study to determine if this process would be effective in further remediating the tert-butyl alcohol (TBA) and MTBE plumes at the site. The site currently has 19 monitoring wells, including MW-1 through MW-6, MW-8 through MW- 11 and MW-14 through MW-22C. Well MW-7 was abandoned in 1996, and wells MW-12 and MW-13 were abandoned in May 2006, due to a relative absence of any detection of constituents of concern. Wells MW-1 through MW-6 and MW-9, MW-10, MW-11, MW-14 and MW-19C are located within the site property boundary or in the adjacent vacant lot to the west. Wells MW-8, MW-15 through 18C and MW-20 through MW-22C are located approximately 120 to 500 feet down-gradient from the southern site boundary. Six piezometers (P-1 through P-6) were installed in 2003 in the southwest portion of the site and offsite to monitor the effectiveness of the GWETS. Piezometers P-1 through P-3 were installed to monitor MW-8, and piezometers P-4 through P-6 were installed to monitor MW-14.