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9038OB-SS4 CON-52 4.6 CONTAMINANT QUANTITY ESTIMATES 4.6.1 The quantities of TCE and PCE in soil and groundwater have been estimated from the data presented in this Draft RI/FS Engineering Report. The estimate revises and updates the values presented in Table 4.6-1 of the July 3, 1989 Draft RI/FS report. While there appear to be major differences in the two estimates, it must be noted that.many quite arbitrary assumptions must be made to calculate these quantities. The finding of significance is that there is probably less than one 55-gallon drum each of TCE and PCE in the groundwater and soil at levels above drinking water MCLS in groundwater (5 ug/1 ) , or- above laboratory detection limits in soil (50 ug/kg) . 4.6.2 The TCE and PCE quantities in groundwater were estimated from the contours on Figures 4.3-1 through 4.3-6 and from the data in Table 4.3-3 of this report. Soil and groundwater volumes were estimated by characterizing the areas inside of or between concentration contours as simple geometric shapes (circles, ellipses, rectangles,_,etc.) . Contaminant depths were estimated from the data inr-Table 4.3-3, where available. Lacking data, an arbitrary (and conservative)R assumption was made: where adjacent contours differed by more than a factor of two, the log average value was used. 4.6.3 Recognizing that both ug/1 in water and ug/kg in soil are equivalent to parts per billion by-weight, the computational procedure used was to estimate the number of billions of pounds of soil or water contaminated, and multiply that'-figure. by the parts per billion of contaminant present, to determine directly'the pounds of contaminant present. 4.6.4 The TCE and PCE quantities in soil were estimated from the measured concentrations in the soil borings given in Table 4.0-9 and using the soil gas contours on Figures 4.2-1 and 4.2-2 along with concentrations found in nearby borings to estimate the areal extent of contamination. 4-196