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L approximately 3.05 (10 feet) thick in most locations. This provided a volume of approximately 974 cubic meters. The contaminant masses were calculated by taking 974 cubic meters times the highest concentration detected in any of the three groundwater wells analyzed during fourth quarter 1995. (The analytical.results are presented in Table C-1 of Appendix C.) For instance, the highest concentration found during the quarter for benzene was from Well MW-8 at 16 µg/L. To determine the total mass of benzene the calculation is as follows: I Mass, = 974 m3(16µg/L)(1000L/1m3)(1kg/109µg) = 0A16 kg This calculation used to determine contaminant mass is only one of the areas where a very conservative approach has been taken. The porosity of the soil was shown to be 0.25 (Section 1.3 of this report). The actual mass of soluble contaminant in reality only resides in the pore spaces of the soil. In i other words, only 25 percent of the total volume of soil is pore space holding contaminated water. By not multiplying the answer shown above times the porosity factor, the mass arrived at is four times higher than what could have been used if approached less conservatively.- Using this method of calculation the masses are as follows: • Benzene = 0.016 kg (0.035 lbs) •. Toluene = 0.055 kg (0.121 lbs) • Ethylbenzene 0.019 kg (0.044 lbs) • Xylenes = 0.074 kg (0.163 lbs) Media Parameters: • Effective porosity = 0.20 (conservative value for model, f�! calculated at 0.25 during aquifer testing, Section 1.3 of this report) • Hydraulic Conductivity = 155.8 m/yr (based on aquifer testing) • Hydraulic Gradient = 0.002 ft/ft (measured during quarterly monitoring) • Longitudinal dispersivity = 6.7 m (0:1 times length of flow path) • Transverse dispersivity = 0.67 m (0.1 times longitudinal dispersivity) 9687 D-3 East Bay Municipal Utility District 404297001cr Final Closure Report