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a) N The mass of hydrocarbon in the subsurface was estimated by considering the distribution of hydrocarbon in soil A rough, but conservative estimate of the hydrocarbon load in each area is presented in the following discussion The western soil contamination area is essentially an ellipse with an area of about 530 sq feet Assuming that the soil from 0 to 60 feet in this area contains an average of 3,100 mg/kg TPH (average of maximum concentrations), the mass of hydrocarbon in this zone is 10,800 Lbs The area of contamination near the former underground tanks is considered to be an ellipse with an area of 900 sq R Assuming the soil from 0 to 30 feet contains an average concentration of 4,000 mg/kg, the total mass in the upper zone is 11,880 lbs Assuming the soil from 30 to 60 feet contains an average concentration of 1,300 mg/kg, the total mass in the deeper zone is 3,860 lbs The total hydrocarbon load in this area is therefore 15,740 lbs The area of well TB3 is the third area of significant soil contamination and is estimated to be a cylinder 15 feet in diameter and 35 feet deep If the hydrocarbon concentration in the soil is 1,000 • mg/kg from 0 to 20 feet, the mass in the upper zone is 390 lbs The lower zone from 20-35 feet is assumed to have a TPH concentration of 5,000 mg/kg, indicating a load of 1,460 lbs , or 1,850 lbs total within the cylinder Based on these calculations, a total of approximately 29,000 lbs of hydrocarbon is present in the soil Note All of the above calculations assume a soil density of 110 lbs/cubic foot These calculations provide an estimate of the hydrocarbon load in the subsurface soils and may be used as a guide to monitor the progress of a remediation effort However, it must be recognized that this is only a rough estimate based on several reasonable assumptions The actual hydrocarbon load in the soils could differ dramatically from this estimate I Page 4