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7hN3dwveII&RoMD <br /> • <br /> A summed estimated total lifetime excess cancer risk of 1E-06 is considered a point of departure <br /> in the evaluation of site risks. Because residential exposure scenarios are considered to be a <br /> conservative point of reference, summed estimated total lifetime excess cancer risks no greater <br /> than 1E-06 are generally considered to be acceptable under residential land use. Under <br /> commercial/industrial land use, the presence of risk mitigation measures (i.e., pavement and <br /> building foundations)together with the very conservative assumptions used in the <br /> commercial/industrial exposure scenario (i.e., ingestion of soil and dermal contact with soil for <br /> an office worker) result in consideration of target risks of 1E-05 or 1E-04. The higher target <br /> risks are considered for the commercial/industrial land use scenario because future exposure is <br /> generally significantly less than that estimated for the risk assessment. <br /> Regulatory guidance for using the target risks discussed above are presented in the National Oil <br /> and Hazardous Substances Pollution Contingency Plan (NCP, 40 Code of Federal Regulations <br /> Part 300.430) and EPA guidance documents. According to the NCP, acceptable exposure levels <br /> • for humans are generally concentration levels that represent an excess upper bound lifetime <br /> cancer risk to an individual of between 1E-04 to 1E-06. The 22 April, 1991 USEPA document <br /> titled Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions, states that, <br /> "Where cumulative carcinogenic site risk to an individual based on reasonable maximum <br /> exposure for both current and future land use is less than 104, and the noncarcinogenic <br /> hazardous quotient is less than 1, action generally is not warranted unless there are adverse <br /> environmental impacts." Lead in soil was evaluated using the CaIEPA LeadSpread Pb6 model. <br /> The results of the PEA and Risk Assessment are summarized below. <br /> 1.4.1 Operable Unit 1 <br /> Area 10—No HIs exceeded 1 for any scenario. During the PEA, blood lead concentrations <br /> exceeded child-receptor and industrial receptor soil target concentrations, and were estimated to <br /> represent a potential health hazard. Additional sampling and analysis for the RI indicated that <br /> predicted blood lead concentrations did not indicate hazardous conditions for any receptor. The <br /> • <br /> 6 <br /> 25970318.PGS 15 November 2000 <br />