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F. Amador <br /> March 1 , 1993 <br /> Page 4 <br /> were not detected during air monitoring. However, the <br /> contaminated soil and groundwater does contain volatile <br /> compounds. The air monitoring methods used in this <br /> study may not have been sufficiently sensitive to <br /> detect benzene concentrations in air at toxicologically <br /> significant levels. For example, the air monitoring <br /> results summarized in Table 2-8 of the RI indicate that <br /> the detection limit for benzene in air varied between <br /> 0. 0098 and 0. 042 ppm, or 31. 2 and 133 .7 ug/m3, <br /> respectively. For comparison, the air concentration <br /> associated with the 10"6 excess lifetime cancer risk is <br /> 0. 1 ug/m3 (USEPA, IRIS-2, February 1993) . <br /> C. Groundwater Exposure. Table 7-8 also indicates future <br /> exposure to groundwater is only considered for Zone C, <br /> and risk estimates are based on current concentrations <br /> detected during monitoring. The geologist (Kathleen <br /> Considine, DTSC Program Development and Technical <br /> Support) who reviewed this site noted that <br /> " . . .contaminants will continue to migrate to the deeper <br /> aquifer and possibly move off-site (if this has not <br /> occurred already) . " Considine also stated that "Well <br /> MW-13 . . .may not represent the area of highest <br /> contamination in the deeper zone. . . " ; and also noted <br /> that health risks from use of water in Zones A and B <br /> are not considered in this report (for example, <br /> industrial use of water in the shallow zones) . <br /> Therefore, the risk assessment may significantly <br /> underestimate risk resulting from domestic and/or <br /> industrial use of groundwater. <br /> 8 . Page 7-45. Hazelton Avenue Strip was not considered in the <br /> exposure assessment. However, as stated in the Executive <br /> Summary, page ES-8, "the Hazelton Avenue Strip contains MGP <br /> [manufactured gas plant) residues in soils and has the same <br /> COPC [chemicals of potential concern) as found in Area I" . <br /> This suggests that human exposure and potential health risks <br /> should be evaluated. As explained above (#5 and #6) , <br /> exposure routes and/or receptors should not be /eliminated <br /> just because the site is capped or a deed restriction is <br /> proposed. <br /> 9 . Page 7-55 to 7-58 . Recent EPA guidance (1991) has detailed <br /> procedures for quantifying dermal absorption from household <br /> water use. Therefore, this exposure pathway should be <br /> evaluated and quantified. Dermal surface area and adherence <br /> factors for a residential scenario can be found in EPA <br /> (1991) and DTSC (1992) . <br />