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I <br /> ]RE MST FOR SITE CLOSURE <br />' General Mills Facthty <br /> 2400 West Tumer Road <br /> Lodi, Caiiforma <br /> Delta Project No 40-92-708 <br /> Page 6 <br />' 4.0 DISCUSSION OF SITE CONDITIONS <br /> 4.1 Soil Conditions <br /> Based on the soil data obtained in October 1991 during underground storage tank removal activities, and <br /> May 1992 during soil investigation activities, Delta has estimated the areal and vertical extent of soli with <br /> concentrations of diesel No 6 greater than 100 ppm Figure 6 shows the inferred areal extent of soil <br /> containing TPH as diesel No 6 as indicated by laboratory chemical analyses of nine soil samples <br /> collected from the base of the excavation <br /> Figure 7 is a cross section location map and Figure S presents two cross sections of the tank excavation <br /> area showing the inferred vertical extent of diesel No 6 in soil We believe this to be a reasonable <br /> estimate of the vertical extent for the following reasons 1) The release of heating oil 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 mayor release or a minor release over an extended period of <br /> time would likely have filled the permeable tank backfill material beneath the tanks, resulting in elevated <br /> concentrations of TPH as diesel No 6 in most if not all of the soil samples, 2) Diesel No 6 is relatively <br />' immobile, 3) Staining 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 5) Chemical analyses of soil samples collected <br /> at 35 feet beneath the surface from each boring indicated that TPH as diesel No 6 was not present One <br />' of these soil samples (MW-3-35, Table 2) was collected directly beneath the former tank location <br /> I4.2 Ground Water Conditions <br /> Petroleum hydrocarbons, including TPH as diesel No 6, have not migrated to ground 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 MW-2 is located approximately 15 feet <br /> directly downgradient of the former tank basin <br /> RPT076 TA <br />