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45 East Harding Way, Stockton, California July 22, 1992 <br /> Chevron U S A Products Company Page 5 <br /> ahead of the augers at each sample point Soil samples were field screened using a photo- <br /> ionization detector (PID) One sample from every five-foot interval was sealed with aluminum <br /> foil, capped, taped, labeled, placed on ice in an insulated container and delivered to a State of <br /> California-certified laboratory <br /> Two soil samples from each of the two monitoring well borings and three samples from the <br /> vapor extraction well boring were selected for analysis Each sample was analyzed for <br /> benzene, toluene, ethylbenzene and xylenes (BTEX), and total petroleum hydrocarbons-as- <br /> gasoline (TPH-G) by Environmental Protection Agency (EPA)-approved methods <br /> 50301802018015 Results of the soil sample analyzes are summarized in Table 1 <br /> 34 Monitoring/Vapor Extraction Well Installation <br /> Monitoring wells MW-10 and MW-11 were installed in two of the soil borings, and a vapor <br /> extraction well V-6 in the remaining boring (Appendix B) The wells were constructed of 2-inch <br /> diameter, schedule 40 PVC casing with flush threads, and 0 020-inch-slot well screen The <br /> well screen was installed from depths of 73-75 feet to depths of 43-45 feet below grade in <br /> each groundwater monitoring well, and from 29 to 19 feet below grade in the vapor extraction <br /> well A sand filter was placed around the well screen to a height of approximately 2 feet above <br /> the top of the screen The wells were completed with a bentonite and neat-cement seal to <br /> grade The wellhead was protected by a locking cap and a traffic-rated street box with a <br /> water-tight bolted lid Well construction details are presented in the drill logs (Appendix B) <br /> Each well was then surveyed for vertical control (Appendix C) <br /> 3 5 Monitoring Well Development <br /> The monitoring wells were developed by manual bailing to remove fine-grained sediments from <br /> the well and filter pack Approximately four well volumes were extracted from each well by <br /> this method This technique insures an even sand filter pack, removes fines, and rehabilitates <br /> the borehole sides The fines are drawn from the well by the bailer until the well water is <br /> visibly clear The development water was contained on site in a DOT-approved purge trader <br /> and transported to Chevron's refinery in Richmond, California for recycling <br /> ® GROUNDWATER <br /> �� TECHNOLOGY <br />