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SAF'EWAY MEAT PACKING FACILITY, STOCKTON, CALIFORNIA TIER II RISK BASED CORRECTIVE ACTION FEBRUARY 26, 1996 PAGE 1 - 3 increase in the probability of an individual developing cancer over a lifetime Increases in cancer risks are regulated at levels which can not be readily detected in populations, that is, 1 to 100 additional cancers within 1,000,000 individuals (expressed as the range 1 x 10' to 1 x 10"6) Noncarcinogenic chemicals are believed to have thresholds (expressed as a reference dose or RfD), that is, a dose below which adverse health effects will not occur Multiple safety factors are used to develop RFDs from toxicological and epidemiological data Fifth, the risk of the exposure to a chemical in the environment is characterized by comparing the estimated daily dose of the chemical to the toxicity factors For carcinogens, the result is an incremental probability of an individual developing cancer over a lifetime as a result of exposure to the COI For noncarcinogens, the risk characterization is not a probability of an effect Rather, it is the ratio of the estimated daily dose to the RfD (or threshold concentration) If this ratio is less than one (1), noncarcinogemic health effects are not expected to occur as a result of the exposure 1.2 Stockton Site Risk Assessment Overview The RBCA (ASTM 1995) Tier II protocol was used to establish SSTLs for the site This procedure involved using ASTM-recommended fate,transport, and exposure pathways algorithms with a combination of site-specific values and default assumptions for individual parameters to calculate the SSTLs At the Stockton site, the two Tier II exposure pathways/scenarios that are potentially complete under existing conditions are 0 inhalation of gases emitted into outdoor air from impacted soil, • inhalation of gases emitted into outdoor air from impacted groundwater, and 0131CDJ1 r