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09/02 '00 NED 16 57 FAX 19259469868 MWEST WC l�tj 020 P AGE 3 (1,2 DCA)f 1,3,5-trimethylbenzene(x,3,5- '1V113), and 1,x,4 trimethylbenzene (1,2, TMB)S All of these constituents are conunonly associated with weathemd gasoline, and all of these constituents were considered constituents of potential concern for the purposes of the HRA Soil and ground water data for the subject properties included analysis of total petroleum hydrocarbons(MI-1). Howevex,both ASTM(1996)and USEPA(1989)recommend that evaluation of chemical mixtures should focus on specific chernical constituents(e.g,benzene) that may be present, rather than on an evaluation of the chemical.mixture_ Thus recommendation is based on the follow mg The toxicity of rnvd lues may be higWy variable,particularly in the case of weathd materials such as those present at these sites. CP Little information is available to characterize the toxicity of mixtures ® The tonicity of mixtues is Largely related to the presence of specific constituents For these reasons, this HRA focused on an evaluation of the specific constituents present(e.&,bene) However, with regard to the TPH dete[tlons, it is worth noting that weathezang appears to have restdted in the loss of the morevolatile (and typically more toxic) frachons,as reflected in the most recent sampling event Furthermore, as will be discussed in the following section,the opportunity for any exposure to ,ccrosiituents of potential concern is lemited.both by land use and by the infrequent oecurrenrce of residual compounds IDENTIFICATION OF REALISd AC EX OS URF PA THWA YS The.following subsections describe land use Information for the subject properties,discuss potential exposure patliwvays for seal and ground water,and summarize the realistic exposure pathways for the subject properties Idem ikatlon of these compounds was based on inforrnaton provided M the Closure Report(ERM,1999)regm-dmg the results of ground water sarnpi ft conducted after oxygen rege-wTabing compounds were introduced into the aiordtonng systEm to enhance natural degradation processes.