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C. Dean Hubbard <br /> October 13, 2006 <br /> Page 8 <br /> * acenaphthene used as a surrogate. <br /> ** pyrene used as a surrogate. <br /> Ambient Air Modeling <br /> 8. Geomatrix calculated the soil saturation concentrations, Csat for all COPC (Appendix C, p. 10 <br /> of 63) as a condition to model dust concentrations.(for all non-volatile PAHs) and ambient air <br /> vapor concentrations (for all PAHs considered to be volatile). It is presumed that contaminants <br /> in concentrations exceeding their corresponding soil saturation concentrations exist as a free <br /> product and cannot be modeled using the models described in the report. <br /> The following issues were noted in the table referred to above: <br /> a) The equation used to calculate the Cot is incomplete. The consultant missed the aqueous <br /> solubility parameter, S. However,this seems to be a typo and this parameter is <br /> considered in the calculation. <br /> b) The values for the soil parameters differ from the ones used in the indoor air modeling. <br /> As a result, Geomatrix assumed one type of soil for their indoor air modeling and a <br /> different type for their ambient air modeling. No rationale is provided. <br /> c) The concentrations used to compare to Csat are not the maximum concentrations, and they <br /> differ from the ones shown in Table 1, Analytical Summary of Detected Chemicals in <br /> Soil. <br /> d) As a result, all COPCs appeared to exist in concentrations lower than Csat. <br /> I used the values for soil parameters consistent with the values used in the indoor air <br /> migration modeling and replaced the concentrations shown in the Maximum Concentration Soil, <br /> Cs column with the maximum concentrations provided in Table 1. It appeared that all COPCs <br /> but indeno(1,2,3-cd)pyrene are in concentrations lower than Csat• This chemical is considered <br /> non-volatile and should be considered in the modeling of dust concentrations. The review of <br /> Table 1 demonstrates that indeno(1,2,3-cd)pyrene exceeds its Csat at one sampling point only <br /> (soil mound sample GMX-11). The RWQCB should make a decision about the need of <br /> delineation and removal or grading of the soil containing indeno(1,2,3-cd)pyrene as a free <br /> product. I used the UCL concentration for indeno(1,2,3-cd)pyrene in my further modeling. <br /> 9. Geomatrix modified the volatilization factor equation shown in the US EPA Soil Screening <br /> Guidance to derive the emission rates. I was not able to verify the modified equation due to lack <br /> of details regarding this modification in the report. Geomatrix first calculated the effective <br /> diffusion coefficients in soil, Da. Das were used to calculate the emission rates under industrial <br />