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Observation wells were located a sufficient distance from one another to <br /> allow determination of the groundwater gradient and flow direction through <br /> analysis of water level data collected from these wells. The top of casing <br /> +! of each observation well was surveyed to the nearest 0.01 foot to allow <br /> comparison of water elevations of the wells. The depth to water from the <br /> top of the well casing was measured with an electronic emersion probe. The <br /> water elevation in each well was computed by subtracting the depth to water <br /> from the elevation at the top of the well casing. This procedure was <br /> repeated on several occasions from January to March 1988 in an effort to <br /> observe any fluctuations in groundwater flow direction and gradient. <br /> The hydraulic gradient analysis indicated that well OW-2 was directly <br /> +•• downgradient of the former underground tank location. Two additional wells <br /> were then located, using results of the gradient analysis and the soil vapor <br /> survey, to provide more water quality sampling points downgradient of the <br /> former tank site. These wells (OW-5 and OW-6, see Figure 3) were installed, <br /> developed and sampled in the manner described above. Both wells were <br /> constructed using 2-inch casings with 0.01-inch screen slots. <br /> SOIL SAMPLING AND ANALYSIS <br /> Soil samples were collected during the drilling of the observation well <br /> +r borings at approximately 5-foot intervals using a 2.5-inch inside diameter <br /> split spoon sampler containing three brass tube liners. The sampler was <br /> driven 18 inches beyond the tip of the auger by a 140-pound hammer dropping <br /> 30 inches. The number of blows was counted for each 6-inch interval the <br /> c�. <br /> sampler was advanced. The brass sample tubes were then quickly extracted <br /> from the sampler. The ends of the samples in the two brass tubes closest to <br /> the shoe of the sampler were examined by a geologist and logged according to <br /> the Unified Soil Classification System prior to being labeled, capped, <br /> sealed and placed on ice. The soil collected in the brass tube farthest <br /> from the shoe was logged, placed in a glass airtight container, and held for <br /> headspace analysis. To avoid cross contamination, the sampling equipment <br /> was cleaned with potable water and trisodium phosphate prior to collecting <br /> each sample. <br /> 3286a/BAV100 16 <br />