ARCHIVED REPORTS XR0006257 - Laserfiche WebLink

Home Browse Search

iReport on Additional Site Assessment and First Quarter 2000 Groundwater Monitoring 3 t 7-Eleven Inc Store#17647 1048 W Yosemite Avenue Manteca CA February 22 2400 34 Groundwater Monitoring Well Installation/Surveying On December 21, 1999, three groundwater monitoring wells were installed in the three borings (MW-1, MW-2, and MW-3) 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 approximately 10 to 20 feet below grade in all three locations Sand was placed in each well annulus from the bottom to approximately 2 feet ' above the top of the well screen The well annulus was sealed with approximately 2 feet of bentonite pellets saturated in place on top of the sand pack, and neat-cement grout to approximately 10 inches below grade The wellheads are protected at the surface by locking, water-tight well 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 following well installation (Appendix B) ' 35 First Quarter 2000 Groundwater Monitoring and Sampling On January 25, 2000, 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 Appendix C Subsequent to monitoring, approximately four well volumes of water was removed from each monitoring well to ensure stabilization of pH, electrical conductivity, and temperature 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 Teflon®-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, MTBE and TPH-g using EPA Methods ' 8020/modified 8015 Samples were additionally analyzed for tert-butanol (TBA), MTBE, di-isopropyl ether(DIPE), ethyl-tert-butyl ether(ETRE), and tent-amylmethyl ether(TAME) by EPA Method 8260 Analytical results are summarized In Table 2 I i ! II II l ! I I I' V I el I E IE Jill 1 I I !