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' Risk Quantification <br /> i <br /> In accordance with accepted convention a conservative level of significance was set at a lifetime <br /> incremental increased risk of cancer of 10' for known carcinogens and 10' for possible human <br /> carcinogens and a hazard index of 1 for non-carcinogenic toxic effects. <br /> Existing soil concentrations were calculated by projecting the analytical data from boring MW1 <br /> (the only boring in which contamination was detected in May 1995) through an estimated volume <br /> i ' of soil. The lateral limits of soil contamination were defined by soil borings SBI through SB3 <br /> (May, 1995) and HP4 (November, 1999). The impacted area is approximately 700 square feet <br /> and the impacted interval approximately 15 feet. The volume of affected soil is approximately <br /> ' 10,500 cubic feet. The arithmetic average concentration of each constituent of concern was <br /> calculated from the analytical data from MW 1 with non-detect samples assigned a value of one <br /> half the detection limit. The representative concentrations within the affected soil volume were <br /> ' then computed by assuming that concentrations diminish concentrically to zero at the margins <br /> of the affected area. This results in concentrations within the affected volume of one half the <br /> average concentrations present in MW1, located in the center of the affected area. <br /> 1 <br /> Printouts of the input and output data from the computer program are attached. The results are <br /> ' summarized below: <br /> RESIDENTIAL SETTING: <br /> ' Constituent Avg. Cone. Hazard Index Significant? Cancer Risk Significant? <br /> (mg/kg) <br /> Benzene 0.63 1.3 E-3 NO 1.0 E-7 NO <br /> Toluene 0.63 2.0 E-5 NO NC NC <br /> Ethylbenzene 22.2 2.8 E4 NO NC NC <br /> 1 Xylenes 90.0 1.6 E-4 NO NC NC <br /> SUM 1.8 E-3 NO 1.0 E-7 NO <br /> ' COMMERCIAL SETTING: <br /> Constituent Avg. Cone. Hazard Index Significant? Cancer Risk Significant? <br /> ' (mg/kg) <br /> Benzene 0.63 1.2 E-3 NO 7.1 E-8 NO <br /> Toluene 0.63 1.7 E-5 NO NC NC <br /> ' ]Mylbenzene 22.2 2.3 E4 NO NC NC <br /> Xylenes 90.0 1.4 E4 NO NC NC <br /> ' sum 1.5 E-3 NO 7.1 E-8 NO <br /> valleyvwlreportslrbsl.t:t <br /> 5 <br />