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y <br /> `S <br /> to collect soil samples from the rank cavity. Laboratory <br /> analysis of both soil samples and a composite of three ground <br /> water samples collected from the tank cavity indicated <br /> tal petroleum <br /> I� <br /> detectable llevels <br /> vels Of to enz ne, andttotaloxvIcnes (BTEXand <br /> ) <br /> benzene, <br /> constituents. <br /> Also in August 1986, four 2-inch diameter monitoring wells <br /> (Mw-1 through Mw-4) were installed onsite by KEI. Each of <br /> the four wells was completed to a depth of 20 feet <br /> belpraduct <br /> grade. During initial ground water sampling, <br /> no se <br /> was observed in any of the wells. �Dtersamplesacollected <br /> hydrocarbons were detected <br /> crealin the9ga samples <br /> from t4W-3 and MW--4 ( F <br /> Based on the results of the preliminary investigation w6ork, <br /> three additional 2-inch diameter monitoring <br /> wells (W <br /> through jSW-8) and one 4--inch diameter monitoring well (MVI-5) <br /> were installed by ILEI in January 1987. Monitoring Well MW--S <br /> was installed onsite, while the other three wells were <br /> installed offsite, as shown in Figure 2, <br /> The <br /> maximum TPH concentration detected in soil samples collected <br /> during installation of these four wells was 24 parts per <br /> ee prod-ac;} or sheen was noted in any <br /> million (ppm) • Pio fr <br /> ground water samples collected from the new monitoring wells, <br /> however, analysis of the water samples showed detectable TPH <br /> concentrations ranging from 6.3 ppm to a maximum of 41.0 ppm <br /> in Monitoring Well 14W-5 (Kaprealian, 1987) . <br /> The eight existing ground water monitoring wells were sampled <br /> r at i to 4-month intervals beginning in September 1987. vFree <br /> product was subsequently observed in mW-3, <br /> phase gasoline constituents were W_8,continuouslyetected <br /> five of the wells (MW-4 through MW-8) (- p <br /> The last sampling event performed by KEI was in October 1988. <br /> Based on the results of the initial field activities and <br /> laboratory analysis of the soil <br /> and <br /> rground <br /> bon water <br /> samples, it <br /> had <br /> was apparent that petroleum by <br /> e soil and ground water, and that an <br /> impacted the subsurfac <br /> additional characterization study was necessary to define the <br /> Alton nature and extent of contamination.asupplementalcsitee was <br /> retained by Mobil oil to perform <br /> investigation. <br /> The scope of the supplemental investigation included the <br /> following tasks and activities: <br /> o Review of available records and acquisition of the <br /> - - - - - <br /> necessary-permits. <br /> 2 <br />