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err 1%00 <br /> Results of the soil vapor survey performed in June 1987 indicated that <br /> elevated hydrocarbon levels existed to the northeast (locations V2 and V7) <br /> and, to a lesser extent, the southwest (location V5) of the former tank <br /> site. Elevated hydrocarbon levels were not detected to the east of the <br /> tank, nor further than 60 feet away from the tank in any direction. <br /> w <br /> OBSERVATION WELL INSTALLATION, DEVELOPMENT AND GRADIENT DETERMINATION <br /> To determine the groundwater flow direction and gradient, four observation <br /> wells were installed (OW-1, OW-2, OW-3 and OW-4; see Figure 3) in December <br /> 1987 and January 1988. An attempt was made to locate at least one of these <br /> r.. <br /> wells (OW-2) in a position hydraulically downgradient of the tank site. <br /> Groundwater samples were subsequently collected from all of the wells for <br /> chemical analysis, as recommended by the Central Valley Regional Water <br /> Quality Control Board. <br /> a.. <br /> The screened interval of each well was placed from approximately 3 feet <br /> above the encountered water table to 17 feet below the water table (from 5 <br /> to 25 feet below the ground surface) to allow for seasonal water level <br /> fluctuations. Well permits were obtained from the San Joaquin County Health <br /> Department prior to installation. <br /> +r Each observation well was constructed of flush-threaded schedule 40 <br /> polyvinyl chloride (PVC) casing. Four-inch casing with 0.02 inch slots was <br /> used for wells OW-1 and OW-4. Two-inch casing with 0.01 inch slots was used <br /> for wells OW-2 and OW-3. The filter pack material for all wells was Lone <br /> Star #2/12 sand. This sand was selected primarily for convenience, since <br /> grain size analyses performed on soil samples collected during the initial <br /> investigation showed greater than 90 percent of the sample passing the No. <br /> a.. <br /> 200 sieve (making a designed filter pack infeasible) . Stainless steel <br /> centralizers were used at each well to insure an evenly distributed filter <br /> i' pack. Figure 5 shows the construction of an observation well typical for <br /> this investigation. <br /> •r <br /> J <br /> v <br /> 3286a/BAV100 13 <br />