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Former Beacon Station 494 October 8, 1996 <br /> Stockton, California Appendix B Closure Report <br /> Mass Balance of Petroleum Constituents in Soil and Groundwater <br /> After removal of the USTs, hydrocarbon impacted soil was discovered in soil borings at <br /> depths below 15 feet bsg south of the UST cavity (VW-1 and MW-3) These levels decrease <br /> significantly below 45 and 50 feet bsg Assuming an average thickness of 35 feet (15 to 50) <br /> of impacted soil over the aerial extent of TPHg between the eastern property boundary and <br /> VW-2 (Area 1) equates to approximately 3,600 cubic yards of impacted soil The average <br /> concentration of TPHg reported from the samples collected and analyzed in these soil <br /> borings from between 15 and 30 feet is equal to the average concentration of TPHg of <br /> approximately 850 mg/Kg in the apparent impacted area Assuming an average thickness of <br /> 30 feet(20 to 50) of impacted soil within the aerial extent of TPHg between VW-2 and VW- <br /> 4 (Area 2) equates to approximately 2,250 cubic yards of impacted soil The average <br /> concentration of TPHg reported from the analyzed samples collected from VW-2 and VW-4 <br /> between 20 and 50 feet equal the average concentration of TPHg in the assumed impacted <br /> Area 2 of approximately 119 mg/Kg <br /> Assuming a soil density of 2,800 pounds per cubic yard, Area 1 originally contained <br /> approximately 8,568 lbs of TPHg and Area 2 contained 750 Ibs of TPHg (for a total of <br /> 9,318 lbs of TPHg or 1,479 gallons) These products were obtained using the following <br /> equation <br /> n = (parts of TPHg/1,000,000 parts of soil) x (2,800 lbs of soil per cubic yard ) x <br /> (volume in cubic yards of soil) in lbs of TPHg <br /> Note n= average concentration of TPHg in soil <br /> 1494 APB 10 HORIZON ENVIRONMENTAL INC <br />