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l SAFEWAY MEAT PACKING FACILITY, STOCKTON, CALIFORNIA TIER II RISK BASED CORRECTIVE ACTION FEBRUARY 26, 1996 PAGE 2 - 2 have developed SFs for benzene, STTLs using SFs from both organizations have been developed for the Stockton site Table 3 provides the SFs used in this assessment All of the COIs have potential noncarcinogeruc health effects The USEPA (1995b) reference doses (RfDs) have been used to characteznze the potential noncarcmogemc health threats Noncarcinogeruc chemicals are believed to have threshold concentrations health effects are not believed to occur at doses below certain levels Based on the threshold concept, USEPA has established RID to characterize the muumum exposure which is likely to cause noncaremogeruc health effects The unit of an RfDs is "mg/kg-day " The ratio of the average daily dose of a chemical (in mg/kg-day) to RfD is the hazard quotient or HQ If the HQ is less than 1 the concentration of the chemical in the environment will not result in an individual being exposed above the threshold dose Noncarcmogemc health effects are not expected to occur Table 3 provides the RfDs used in this assessment USEPA does not have an RfD for either 1,2,4-trfinethylbenzene or phenanthracene For this RBCA evaluation, RfDs for these compounds have been selected from related chemicals The surrogate chemicals were based on structure-activity relationships to the COIs The RIDS for xylene has been used to characterize the toxicity of 1,2,4- trimethylbenzene based on the close structural relationship between the two chemicals Xylene has two methyl groups attached to a benzene ring and 1,2,4- tnmethylbenzene has three methyl groups They both cause central nervous system effects and they have similar acute toxicities (Sax and Lewis, 1989) • The RfDs for anthracene have been used to characterize the toxicity phenanthrene Both compounds are planer (or flat) polycyclic aromatic hydrocarbons composed of three benzene rings anthracene is a straight chain of linked benzene rings and phenanthrene is a branched chain D131CDJ1 I