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REQUEST FOR SITE CLOSURE_ <br /> General Muh Fscihcy <br /> 2000 West Turner Road <br /> Loan C'.4:„orna <br /> Delta Project No 4.0-92-708 <br /> Page b <br /> 4 0 DCSCTJSSTON OF SPIE CONDMONS <br /> 4.1 Soil Conditions <br /> Based on the soil data obtained in October t991 during underground storage tank removal activities, and <br /> May 1992 during soil investigation activities, Delta has estimated the areal and vertical extent of soil with <br /> concentrations of diesel No 6 greater than IGO ppm Figure 6 shows the inferred areal extent of soil <br /> containing TPH as diesel No 6 as indicated by laboratory chemical analyses of time soil samples <br /> coilected from the base of the excavation. <br /> Figure 7 is a cross section location man and Figure 8 presents two cross sections or the tank excavation <br /> area showing the inferred vertical extent of diesel No 6 m soil. We believe this to be a reasonable <br /> estimate of the vermcal extent for the tollowmg reasons. 1) The release of heating od was likely limited <br /> in volume because elevated concentrations of diesel No 6 in the base of the former tank excavation were <br /> limited in extent as shown in Figure 6 A major release or a minor release over an extended period of <br /> time would likely have tilled the permeable tank backfill material beneath the tanks, resulting m elevated <br /> concentrations of TPH as diesel No 6 m most if not all of the soil samples, 2) Diesel No. 6 is relatively <br /> immobile, 3) Staming indicative of fuel contamination was not present in soil samples collected from the <br /> borings for the monitoring wells, 4) Organic vapors were not detected with the PID in soil samples <br /> collected from the borings for the monitoring wells; and 35) Chemical analyses of soil samples collected <br /> at 35 feet beneath the surface from eacn boring Indicated that TPH as diesel No 6 was not present. One <br /> of these soil samples (1Lv1W-3-35, Taole 2) was collected directly beneath the former tank location. <br /> 4.2 Ground Water Condition <br /> Petroleum hydrocarbons, including TPH as diesel No 6, have not migrated to ,round water beneath the <br /> site Depths to ground water in monitoring wells beneath the site have ranged between approximately 39 <br /> and 42 feet (24 to 27 feet beneath the base of the tank basin) Concentrations of TPH as diesel No 6 <br /> have not been detected in three monitoring wells adjacent to the former tank locations during four <br /> quarters of ground water monitoring at the site Monitoring well IMW-2 is located approximately 15 feet <br /> directly downgradient of the former tank basin <br /> xvrCF76 TA <br />