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3.0 SITE CONCEPTUAL MODEL �+ 3.1 Source Area Evaluation The former UST source area is located on the east side of the mausoleum building (Figures 2 and 3). Soil samples collected from beneath the former USTs and from soil borings drilled in the vicinity of the former USTs indicated that impacts to subsurface soil were concentrated beneath the USTs between approximately 10 and 30 feet bgs, and that concentrations of gasoline compounds in vadose zone soil declined with depth but extended to the groundwater table. The lateral extent of TPH-as-gasoline in soil prior to remedial action is �.. shown on Figure 9, and the vertical distribution of impacted soil prior to remedial action is shown in two cross-sections (Figures 10 and 11). t.. 3.1.1 Petroleum Hydrocarbon Mass in Soil Pre-Remediation �,. Based on the distribution of impacted vadose zone soil as interpreted in Figures 9, 10 and 11, the volume of impacted soil is best approximated as two stacked cylinders. The upper cylinder, containing the bulk of the impacted soil, has a radius of 20 feet and extends from 10 to 30 feet bgs. The lower cylinder extends from 30 to 65 feet bgs and has a radius of 30 feet. As such, the volume of impacted soil would be described as follows: V upper cylinder:= TTI2(1) =TT(20)2(20) = 25,132 W V lower cylinder= TrI72(I) =TT(30)2(35) = 98,960 W �.. Referring to the cumulative soil sample analytical results (Table1), the average .. concentrations of TPH-as-gasoline and benzene in the upper and lower cylinders are as follows: TPHg upper cylinder �Ot 4,200+2,200+2,500+240+12,000+1,000)17 Samples { (22,140 ppm)/7 = 3,163 ppm Benzene upper cylinder= (0+21+6.1+14+1+26+0)ppm17 Samples v = (68.1 ppm)17 = 9.7 ppm TPHg tower cylinder = (1.5+20+1.1+0+0+0+0+0+0+2.2+0+0+0+0+0+1.6+21+0+0)1 19 Samples = (47.4)119 = 2.5 ppm Benzene lower cylinder=(0.005+1.8+0.14+0.013+0+0.04+0.08+0+0.14+0.34+0+0+0+0+ 0.024+0.26+0.61+0)119 Samples = (3.5 ppm)/19 = 0.2 ppm � 11