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5.0 Mass Balance of Petroleum Hydrocarbon Quantities ` sl . 5.1 Mass Balance of Contaminants in Groundwater The mass quantity of TPH gasoline and diesel in the upper groundwater zone was calculated using the inferred water contamination levels and plume size as indicated in the Quarterly Groundwater Monitoring and Sampling Report, Third Quarter, 2002 Sampling Event. The areal extent of the contaminated groundwater at the water table is estimated to be 8000 square feet for the gasoline plume and 1000 square feet for the r more limited diesel plume. The vertical extent of the highly contaminated groundwater in the upper saturated zone,is estimated to be ten feet for eh,terstitial volume of 24,000 cubic feet or 680,000 liters (L) of water with gasoline contamination and 3,000 cubic feet or 85,000 L of water with diesel contamination in the upper water zone, assuming an average soil porosity of 30% The extent of the gasoline plume was broken down into three concentric rings representing decreasing contaminate values as you move from the center outward. The inner ring with an estimated volume of 110,000 L was given an average gasoline contaminant value of 40,000 µg/L. The second and third.rings were estimated at 230,000 L and 340,000 L with average contaminant values �Iof 5,.000 pg/L and 500 pg/L, respectively. These values calculate out to a mass of 5.7 kilograms (kg) of TPH gasoline in the upper, most contaminated, groundwater zone. The gasoline mass below the upper ten feet is expected to be much less since gasoline is a LNAPL. j The smaller diesel plume with an estimated volume of 85,000 L was given an average diesel contaminant value of 400 µg/L. These values calculate out to a mass of 0.034 kg of TPH diesel in the upper groundwater zone. The diesel mass below the Upper ten feet is expected to be much less if not zero. �I 5.2 Mass Balance of Contaminants in Soil { The mass quantity of TPH gasoline and diesel in the impacted soil above the groundwater table is calculated using analytical data-from the soil samples collected when installing .monitor wells MW-2 and MW-5 which are located in the former UST tank excavation areas. The volume of impacted soil is calculated using a thickness of 20 feet (estimated UST excavation bottom to the groundwater,, table) and an estimated areal extent of 100 square feet per excavation producing a ivolume of 2000 cubic feet per excavation. Analytical data from the monitor well soil samples collected under the gasoline UST excavation infer a vertical average of 6700 mg/Kg of TPH gasoline. The contamination value is assumed to be zero as you move laterally away from the impacted soil zone. Assuming a soil density of 45 kg per cubic foot, the impacted soil is estimated to have a mass of 90,000 kg. JJW calculates the estimated mass of gasoline in place in the soil above the groundwater table to be 600 kg. Based on'`:the monitor well soil data JJW infers that there is probable gasoline contamination absorbed to the soil below the current groundwater table. However, there is currently not enough data to calculate the mass. Analytical data from the monitor well soil samples collected under the diesel UST excavation infer a vertical,average of 4600 mg/kg of TPH diesel.. JJW calculates the 4 JJW GEOMENCES lnC.