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Ms. Barbara Marcotte • <br /> Page 4 <br /> The value for tetrachloroethylene (PCE) is also incorrect, and <br /> the reference to the value used is not the primary citation. The <br /> report cites a value reported in a health effects document for <br /> beryllium. The value published in the beryllium document is an <br /> oral potency factor, not an inhalation potency factor, and <br /> originates from an EPA health effects document for PCE. PCE is <br /> currently under review by an IRIS workgroup and subject to <br /> change. The most current inhalation potency factor for PCE is <br /> given in the Superfund Public Health Evaluation Manual (19 6) as <br /> 0. 0017 rather than the oral potency of 0. 051 used on p. 16 of the <br /> risk assessment. This results in an air criterion of 2 . 06 ug/m3 . <br /> The error does not significantly alter the conclusions in Table <br /> 6. 1 <br /> Exposure Assessment: <br /> Since there is no resident population at Valley Haven a this <br /> time, the risk assessment cannot address high risk human <br /> receptors such as children, elderly or the infirm. Instead the <br /> target receptors are two imaginary individuals, the maximally <br /> exposed individual and an "average" individual. This is an <br /> accceptable approach for this particular risk assessment. In <br /> addition, both of these individuals are assumed to live at Valley <br /> Haven for a 70 year lifespan (life must be good at Valleyaven) . <br /> The exposure assessment modeling includes estimating the r to of <br /> volatilization of VOC's from soil, and estimating the ambi t air <br /> concentrations at the two receptor locations from on-site Blease <br /> of VOCs, atmospheric transport of SHAD soil VOC emissions to <br /> Valley Haven, and the release and transport of the SHAD air <br /> stripping tower emissions to Valley Haven. All of the emission <br /> rate models and air dispersion models are DHS and EPA recommended <br /> models and the parameter values used in the equatio s are <br /> reasonable assumptions, estimates and/or values. The contractors <br /> have done an exceptional job of incorporating all the data <br /> available to them in the use of these models. There will always <br /> be an unknown degree of uncertainty in the results, since there <br /> are many different assumptions which must be made. However, given <br /> the inherent conservatism of these models and assumptions (a <br /> point which is well made in the report) , the predicted air <br /> concentrations averaged over the course of a year should be an <br /> overestimate. <br /> Risk Characterization: <br /> The predicted air concentrations are compared to the health based <br /> criteria values using the Decision Tree test methods. All f the <br /> predicted air concentrations are at least two orde s of <br /> magnitudes lower than de minimis risk values. Therefore it is <br /> reasonable to conclude that no significant health impacts will <br />