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• August 3, 1988 sky AGS Job No. 86091-6 Page 3 2 to 3 feet above the top of the screen. A 1- to 2-foot-thick bentonite seal was placed above the sand to prevent cement from entering the sand pack. The remaining annular space was backfilled with neat cement to grade. Wells VW-6 and VW-9 were installed in the tank cavity in sheet- metal utility boxes with steel lids. The utility boxes had been installed when the conductor casing and backfill material were placed during replacement of the central underground tank. Cast- aluminum utility boxes with PVC aprons were placed over the well heads of wells VW-7 and VW-8 and were set in concrete flush with the surrounding station pad. All the utility boxes have a watertight seal and require specially designed wrenches to open. Piping that connects the utility boxes containing the vapor- recovery wells and monitoring wells MW-1, MW-2 , and MW-4 with the proposed blower assembly area was installed during replacement of the central underground storage tank. The piping system consists of individual 1-inch-inner-diameter, PVC pipes that run from each vapor--recovery or monitoring well to the proposed blower assembly area. The individual connective pipes are enclosed in 4-inch- inner-diameter acrylonitrile butadiene styrene (ABS) conduit. The layout of the 4-inch ABS conduit is depicted on Plate P-2. The casing of each vapor-recovery well is capped with a PVC well head equipped with both 1-inch and 2-inch orifices with standard nominal pipe threads. At this time, the piping is not connected, and the vapor-recovery well heads are plugged with galvanized plugs. Selected soil samples collected while drilling borings B-6 through B-9 were analyzed by Environmental Protection Agency (EPA) Method 8020 for total volatile hydrocarbons (TVI ) and the volatile hydrocarbon constituents benzene, ethylbenzene, toluene, and total xylene isomers (BETX) . All analyses were performed at Applied GeoSystems' laboratory in Fremont, California, which is certified by the State of California for the specified analyses. The results are summarized in Table 1, and copies of the laboratory Records of Analysis are attached to this letter. The results of the laboratory analyses and those performed during previous phases of our investigation (summarized in AGS Report No. 8691-6, dated May 26, 1987) suggest that 1) the contamination levels are highest in soil near the north end of the tank cavity, and 2) the levels of contaminants decrease to 1 part per million or less with depth below or distance from the tank cavity.