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EPA policy must be considered when interpreting the significance of cancer risk <br /> estimates. In the National Oil and Hazardous Substances Pollution Contingency Plan <br /> (NCP) (40 CFR Part 300), EPA states that: "For known or suspected carcinogens, <br /> acceptable exposure levels are generally concentration levels that represents an excess <br /> upper-bound lifetime cancer risk to an individual between 10' and 10'." The EPA <br /> further states, in the preamble to the NCP, that the 1 x 10' risk level should be used as <br /> a point of departure for establishing remediation goals for chemicals at specific <br /> hazardous waste sites. Current EPA guidance,however,,states that where the cumulative <br /> site risk to an individual based on reasonable maximum exposure is less that 1 x 10'. <br /> remedial action is generally not warranted (EPA 1991c). For the Yellow Freight Site <br /> a carcinogenic risk level of 1 x 10' was used as the target risk level for evaluation of <br /> potential exposures in this risk analysis. <br /> EPA guidance to evaluate cancer risk from simultaneous exposure to several carcinogens <br /> ,. assumes that incremental cancer risks are additive. The concept that cancer risks are <br /> additive is based on a number of assumptions. If these assumptions are incorrect, over- <br /> or under-estimation of the actual risk could result (EPA 1989b). .The total cancer risk <br /> is estimated by summing the risk estimated for each.chemical of concern and for each <br /> pathway. <br /> 6.2.3 Risk Quantification <br /> The potential for noncarcinogenic health effects, expressed as-the hazard index, is <br /> calculated as shown below: <br /> ` I <br /> Chemical Intake Daily Hazard <br /> Concentration Factor Intake RfD Quotient <br /> (mg/kg) (kg/kg/dav) (mg/kg/day(mg/ke/day) (unitless) <br /> A B _ C ' D "E <br /> Daily Intake = (Intake Factor)(Chemical Concentration) <br /> C = (13)(A) <br /> i <br /> I <br /> i <br /> S:\LDC\YELLO.M May 4, 1995 6-4 <br />