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C. Dean Hubbard • • <br /> October 13, 2006 <br /> Page 5 <br /> Following the consultant's approach, I used the data as input to the US EPA ProUCL <br /> statistical software to calculate two sets of exposure point concentrations - one set based on <br /> surface soil data(up to 2 ft bgs), and another one based on surface and subsurface data (up to 10 <br /> ft bgs). All non-detects were substituted with a proxy concentration equal to one-half of the <br /> reporting limit. The calculated UCLs are shown in the table below: <br /> Calculated Surface and Surface plus Subsurface UCL Concentrations <br /> Chemical Surface soil UCL Surface plus <br /> concentrations, Subsurface soil UCL <br /> in mg/kg concentrations, <br /> in mg/kg** <br /> Acenaphthene NA 0.46 <br /> Acenaphthylene NA 0.17 <br /> Anthracene NA 0.11 <br /> Benzo(a)anthracene 0.23 0.36 <br /> Benzo(a)pyrene 1.32 0.28 <br /> Benzo(b)fluoranthene 0.18 0.35 <br /> Benzo(k)fluoranthene 0.37 0.23 <br /> Benzo(g,h,i) erylene 0.3 0.17 <br /> Chrysene 0.69 1.09 <br /> Dibenzo(a,h)anthracene 0.1 0.15 <br /> Fluoranthene 0.33 0.5 <br /> Fluorene NA 1.33 <br /> Indeno(1,2,3-cd) yrene 0.15 0.23 <br /> Naphthalene NA 1.51 <br /> Phenanthrene 0.11 2.61 <br /> Pyrene* 1.1 0.92 <br /> Notes: <br /> NA Chemical not considered (all results being non detects) <br /> * Based on maximum(the lower of maximum and UCL) <br /> ** Used in OEHHA's modeling and risk/hazard calculations <br /> Volatile vs. Non Volatile PAHs <br /> 6. The determination of volatile and non-volatile chemicals is important because it determines <br /> the number of chemicals to be assessed under each exposure pathway and may result in different <br /> levels of exposure, hazard, and risk. Geomatrix identified sixteen PAHs as COPCs at this site. <br /> Six of them,namely acenaphthene, acenaphthylene, antracene, fluorine, naphthalene, and <br />