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REPORT ON ADDITIONAL SITE ASSESSMENT AND RECOMMENDATIONS 4 7-Eleven Store No 14117,2725 Country Club Blvd,Stockton,CA December 12,2001 ' 34 Groundwater Monitoring Well Installation/Surveying On October 30, 2001, groundwater monitoring wells MW-5, MW-6, and MW-7 were installed at the ' locations shown on Figure 2 The groundwater monitoring wells were constructed of 2-inch-diameter, Schedule 40 polyvinyl chloride casing with flush threads, and 0 020-inch-slot well screen The well screen was Installed from about 5 to 20 feet below grade In each well Sand was ' placed in each well annulus from the bottom to approximately 1 foot above the top of the well screen The well annulus was sealed with approximately 3 feet of bentonite pellets saturated in place on top of the sand pack, and concrete to approximately 6 Inches below grade The wellheads are protected at the surface by locking,water4ightwell caps and traffic-rated street boxes (with watertight bolted lids) set In concrete Well construction details are shown on the drill logs in Appendix A The top of casing and rim of each well box was surveyed by Morrow Surveying for horizontal position and elevation relative to mean sea level datum (Appendix B) ' 35 Fourth Quarter 2001 Groundwater Monitoring and Sampling On November 5, 2001, depth to water in each well was measured to the nearest 0 01 foot from the top of the well casing using an interface probe (Table 2) Field data sheets are provided in IPAppendix C ' Subsequent to monitoring, approximately four well volumes of water was removed from each of the older monitoring wells to ensure stabilization of pH, electrical conductivity, and temperature About 10 well volumes of water was removed from each of the new wells (MW-5, MW-6, and MW-7) to ' complete well development The purge water was stored in DOT-approved 55-gallon drums pending transport and disposal Prior to groundwater purging,dissolved oxygen was measured in each well ' using a field instrument The groundwater samples were collected using disposable bailers,then transferred to 40-milliliter glass vials filled to zero headspace and acidified to a pH of 2 The samples were sealed using TeflonO-septum caps, labeled, placed on ice in an insulated container, and ' transported under chain-of-custody to a state-certified laboratory for analysis The groundwater samples were analyzed for BTEX and TPH-G using EPA Methods 8020/modified 8015 Samples ' were additionally analyzed for TBA, MTBE, DIPE, ETBE, and TAME by EPA Method 8260 (Table 1, Figure 2) 1