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October 13, 1988 <br /> AGS Job No. 86102-3 <br /> Page 3 <br /> Piping that connects the utility boxes containing the vapor- <br /> recovery wells and monitoring well MW-1 with the proposed blower <br /> assembly area was installed during replacement of the pea gravel <br /> backfill. The piping system consists of individual 1-inch-inner- <br /> diameter, PVC pipes that run from each vapor-recovery well or <br /> monitoring well to the proposed blower assembly area. The <br /> individual connective pipes are enclosed in 4-inch-inner-diameter <br /> acrylonitrile butadiene styrene (ABS) conduit. The layout of the <br /> 4-inch conduit is depicted on Plate P-2. The casing of each <br /> vapor-recovery well is capped with a PVC well head equipped with <br /> both 1-inch and 2-inch orifices with standard nominal pipe <br /> threads. At this time, the piping is not connected, and the <br /> vapor--recovery well heads are plugged with galvanized plugs. <br /> Selected soil samples were analyzed by Environmental Protection <br /> Agency (EPA) method 8020 for total volatile hydrocarbons (TVH) <br /> E and the volatile hydrocarbon constituents benzene, ethylbenzene, <br /> toluene, and total xylene isomers (BETS:) . All analyses were <br /> performed at Applied GeoSystems' laboratory in Fremont, <br /> California which is certified by the State of California to <br /> perform these analyses. The results are Summarized in Table 1, <br /> and copies of the laboratory Records of Analyses are attached to <br /> this letter. <br /> ' The results of the analyses performed during previous phases of <br /> our investigation (summarized in AGS Report 86102-2, dated May <br /> 26, 1987). indicated .that hydrocarbon contamination originated at <br /> the north end of the tank cavity. The results of the laboratory <br /> analyses of soil samples obtained from the vapor-recovery wells <br /> f are consistent with this interpretation. Concentrations of total <br /> volatile hydrocarbons in samples from borings B-6 and B-7 (vapor- <br /> recovery wells VW-4 and VW-5, respectively) exceed 750 ppm, while <br /> the concentrations in samples from borings B-8 and B-9 (vapor- <br /> recovery wells VW-6 and VW-7, respectively) are less than 50 ppm. <br /> Because the detected levels of soil and ground-water <br /> contaminaticn are highest in borings and wells immediately <br /> adjacent to the tank cavity (MW-1, MW-2, Ver'-4, and VW-5) , it is <br /> inferred that dominant contaminant transport direction was <br /> downward. <br /> i <br /> MIME <br />