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The volume of diesel within this packet of soil is computed by multiplying the volume by the mean • concentration for the depth interval and using the appropriate conversion factors for parts per million and gallons per cubic foot Vgas=Vsoil x [(K35 + K40)- 21 x 1 x 7 48 gal/W 60- 1,000,000 , 7 r ► 11cy = � 7rj/rs 00 6 = 1,588 ft' x [(7,500+ 6,0001- 21 x 7 48 gal/ft3 '^ Pu III Pe 1,000,000 ,5$8 �F IZS Iblft3 I93, 500 rb = 80 15 gal � 7r,5�If, x ,00G7r1 1339-�zs 1L dc�s--f The volume of diesel remaining in place was then multiplied by the weight of diesel fuel per gallon to obtain an estimate of the mass of remaining fuel The mass is needed in order to model the fate of the contaminants Ion ��j F{ &AZI} qLF 158,8 KI tdyl,9 ib �csc 15u g&O_ ;hcs-( 3 0 RESULTS 3 1 Analytical Results----Soil Of the thirty-two samples that were analyzed, diesel fuel was detected above the 1 mg/kg reporting limit in twenty-three Diesel was detected in all thirteen samples from GT-22, which is the only boring that was drilled near the former UST cavity(Table 1) The maximum concentration detected within the Modesto Channel aquifer was 14,100 mg/kg at the top of the channel (depth 35 feet), but a slightly higher concentration was detected dust below the base of the channel (14,400 mg/kg at 55 feet) It appears that this boring penetrated the contaminant plume dust to the east of its center within the channel (Figure 3) Higher concentrations (15,500 and 20,200 mg/kg) were detected in and below the 15' Riverbank Channel near the base of GT-22, and it appears that within the Riverbank Formation, the centei of the plume may be located slightly more to the east than in the overlying Modesto (Figure 3) Boring GT-22 did not reach the base of the contaminant plume, which may be within the 2nd Riverbank aquifer or within the clayey paleosol that overlies it For the most part, borings GT-23, GT-24, and GT-25 define the eastern and western limits of the contaminant plume All three borings penetrated mostly uncontaminated soil, but did encounter low to moderate diesel concentrations in the lower part of the Modesto Channel and/or in the 1St Riverbank Channel (Figures 4 and 5) Borings GT-21 and GT-26 illustrate the importance of the Modesto Channel in confining and channeling the movement of the diesel fuel laterally through the soil Samples at 50 feet in both borings (base of the channel) were contaminated, whereas samples above and below were not (Table 1) This implies that the diesel fuel migrated eastward within the permeable gravel that overlies the base of the channel for a distance of more than 180 feet In contrast, cross-channel • 4