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S <br /> a <br /> F <br /> } <br /> s with 5030 extraction. The excavated native soil produced by the <br /> F borings was covered with polyethylene liners, but laboratory <br /> results show that this soil has very low contamination levels and <br /> this soil was aerated and used for back filling of depressions in <br /> - - the lot. - - <br /> Y <br /> SOIL CONTAMINATION <br /> Soil samples of the tank excavation and nearby monitor wells <br /> indicate that gasoline range hydrocarbons are found between the 30 <br /> and 40 foot depths southeast of the excavation. Soil samples <br /> taken from the base of the three pump island excavations, <br /> indicated that contaminated soil remains beneath the eastern and <br /> western pump island areas at the 40 foot depth but has been <br /> removed from the center pump island by the excavating, see Figura <br /> 3B. Two estimates of total petroleum hydrocarbons remaining in <br /> the soil were made after the vapor extraction pilot test, see <br /> Table 2. The first estimate is based on averaging the <br /> concentration in the soil and calculating the area, shaded on <br /> y Figure 3B, of the contamination as a cube, approximately 1560 <br /> pounds of hydrocarbons remain after the pilot test. The second <br /> estimate is based on the highest concentration found for that area <br /> and calculated that area as a cube, approximately 2870 pounds of <br /> hydrocarbons remain in the vadose zone (25 foot depth to the 40 <br /> foot depth) after the pilot test. <br /> SLUG TEST <br /> On November 27 1990, WEGE performed a slug test on all of the <br /> ground water monitoring wells (Mwl, MW2, MW3, MW4, MW5, and MW6) . <br /> Using the Bouwer and Rice method for predicting hydraulic <br /> conductivities (K) ground water velocities were calculated. The <br /> results of the slug test showed that the formation near the wells <br /> is of a silty fine sand with the highest ground water velocity <br /> being near MW1 and forms a velocity dome at this well which <br /> spreads southeast and northwest towards monitor wells MW6 and <br /> xTJ2, see Figure 41%'11. Figure 48 physical grouT3 water level (dashed <br /> line) closely resembles this velocity map. Using the velocity <br /> from MW2, down gradient well, the contaminant plume would travel <br /> less than 4 feet in one year. <br /> MONITOR WELL CALCULATED K CALCULATED VELOCITY <br /> FT/DAY FT/DAY <br /> MW1 1.58 0.12 <br /> MW2 0.39 0.01 <br /> MW3 0.03 5.2XIO-4 <br /> MW4 0.21 4.1X10-3 <br /> MW5 0.51 0.01 <br /> MWF 1.99 0.06 <br /> k <br /> r� <br /> ti <br /> t <br /> page 6 <br />