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t <br /> i <br /> i <br /> with 5030 extraction. The excavated native soil produced by the, <br /> 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 /> 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 Figure <br /> 3a. Two estimates. of total petroleum hydrocarbons remaining in <br /> the soil were made after the vapor extraction pilot test, see <br /> 1 Table 2. The first estimate is based on averaging the <br /> concentration in the soil and calculating the area, shaded on <br /> Figure 3B, of the contamination as a cube, approximately 1860 <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 (MWI, MW2, MW3, MW4, MWS, and HW6) . <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 HWS and <br /> HW2, see figure 4C. Figure 4B physical ground water level (dashed <br /> line) closely resembles this velocity map. Using the velocity <br /> t from MW2, down gradient well, the contaminant plume would travel r <br /> t less than 4 feet in one year. <br /> -- ------ -- ----:-.-- MONITOR—WELL--- -.---CALCULATED K CALCULATED VELOCITY - ------ -- — - - <br /> FT/DAY FT/DAY <br /> MW1 1.58 0.32 <br /> MW2 0.39 0.01 <br /> MW3 0.03 5.2X10-4 <br /> MW4 0.2.1 4.1X20-3 <br /> MWS 0.51 0.OI <br /> HW6 1.99 0.06 <br /> page 6 <br />