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SECTIONTHREE 4®chalccl Approach <br /> 1 RfD(x) = Reference Dose, a chemical-specific dose value based on a no- <br /> observed adverse effect level(i e,threshold level) <br /> Hazard quotients may be summed for all compounds of concern and pathways to yield an overall <br /> hazard index However, this approach is conservative because the nature of non-carcinogenic effects <br /> (i e, organ injury) does not always support a basis for additivity In reality, non-carcinogenic effects <br /> may or may not be additive Hazard indexes will be calculated for each exposure pathway and <br /> population, under average and RME assumptions When a hazard quotient is greater than 1, it will be <br /> recalculated by only summing exposures for chemicals which have the same toxic manifestation effect <br /> on the same target organ, as specified by agency guidance <br /> The product of the human health screening evaluation is thus a compilation of carcinogenic risks and <br /> non-caranogenic hazards, for each area of concern at the site, for each pathway, and each receptor <br /> population Non-carcinogenic hazards are considered acceptable if hazard indexes are below 10 <br /> r <br /> � � ® C%CALTRANS04OPICIWRKPLNFDOa7-0CT4m73owNA%SNA 3-9 <br />