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Table B-1 shows the calculations and the estimate of chemicals removed at each former <br /> tank location As shown, the estimated mass of chemicals removed at former tank sites 1 <br /> and 2 is 847 and 308 pounds, respectively <br /> Mass Remaining <br /> 1 <br /> Ground Water <br /> To estimate the mass of chemicals remaining in ground water at each former tank site, it <br /> was necessary to mathematically extrapolate the concentrations present between ground <br />' water samples The results of ground water samples collected in monitoring wells at the <br /> site during the most recent sampling event (29 February 2000) were used in conjunction <br /> with the results of HydroPunch samples previously collected to create contours of the <br />' TPH-g and benzene concentrations at each former tank site These contour maps are <br /> presented as Figures B-1 through B-4 As shown, HydroPunch samples collected between <br />' monitoring wells were not used for contouring purposes These HydroPunch samples <br /> were excluded from contouring because (1) the monitoring well samples collected in <br /> February represent the current conditions at the former tank sites (the HydroPunch <br />' results are 1 to 2 years old), and (2) the HydroPunch results represent the concentrations <br /> at a point, not an average, over the depth of impacts <br /> Using the contours shown in Figures B-1 through B-4, ERM estimated the surface area <br /> between each logarithrruc ground water concentration contour (e g, between 100 and <br />' 1,000 µg/1, 1,000 and 10,000 gg/1) The mass of cherrucals was then determined by <br /> multiplying the surface area between each contour by the average concentration between <br /> each contour, the average depth of ground water impacts, and the porosity of the aquifer <br />' The logarithmic mean value between contour was used as the average concentration for <br /> each area An assumed depth of 15 feet was used for the depth of ground water impacts <br /> A porosity of 0 40 was used for the calculations <br />' Table B-2 presents the calculations performed and the estimates of chemicals remaining in <br /> ground water at each former tank site As shown, the total mass of chemicals estimated to <br />' be present at former tank sites 1 and 2 is 25 5 and 9 5 pounds, respectively The <br /> calculations estimate that 0 27 and 0 23 pound of benzene are also present in ground water <br />' at former tank sates 1 and 2, respectively <br /> Soil <br /> IAt former tank site 1, confirmation samples collected along the north, west, and east <br /> sidewalls of the final tank excavation (UST 1-4, 1-8, and 1-9) indicate that benzene was <br /> completely removed from soil and the residual concentrations of TPH-g are low (i e , 32, <br /> <5, and 6 4 mg/kg, respectively) Excavation was performed to the south as far as <br /> possible, but was stopped approximately 3 feet short of a loading dock to the south due <br /> B-2 <br />