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The hydraulic gradient ( i) at shallow depths under the site, <br /> based on the gauging of wells EA1 through EA4, was about 0.001 in <br /> April 1988. Assuming a hydraulic conductivity (K) -for shallow <br /> sand or silty sand of 1x10-4 meters per second (m/sec) and an <br /> effective porosity (n) of 0.3, the ground-water velocity of the <br /> shallow aquifer may be calculated as <br /> V = Ki/n <br /> = 10.5 m/year ( 35 feet/year) . <br /> This is an order of magnitude slower than the estimated velocity <br /> based upon previous data ( Section 2. 1 . 1 ) , due principally to <br /> lower conductivity of the materials logged in the shallow EA <br /> wells. <br /> _ 3.2 RESULTS OF SOIL AND GROUND--WATER ANALYSES <br /> Soil samples were collected from each new boring <br /> at 5 -foot inter- <br /> vals starting at a aep_h of 5 feet. Each sample was screened <br /> with a Foxboro volatile organics analyzer (VOA) for the presence <br /> of hydrocarbons. Because all soil samples from borings EA1 <br /> through EA3 appeared to be free of hydrocarbons, only one sample <br /> from each borehole, collected just above the water table, was <br /> sent to the laboratory for analysis. From boring EA4, two <br /> samples were selected for analysis, because hydrocarbons were <br /> detected in the sample taken at 36 feet. Samples were analyzed <br /> by gas chromatograph for BTXE and for TPH as gasoline, using EPA <br /> Methods 8015 and 8020. Neither BTXE or TPH was detected in any <br /> sample above the reporting limits: 5 mg;kg for TPH; 0 .2 mg/kg <br /> for benzene, toluene, xylenes, and ethylbenzene. <br /> Water samples from all wells were analyzed for BTXE and for TPH <br /> as gasoline (Table 2 ) . The highest levels of hydrocarbons were <br /> found in MW2 and MW3, but these were only 0 .25 mg/L - f TPH. <br /> Concentrations of benzene, toluene, xylenes, and ethylbenzene <br /> (BTXE) in these two wells were also low. The highest <br /> c23/72g2 8 <br />