SITE INFORMATION AND CORRESPONDENCE

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f . 0 • C. Dean Hubbard October 13, 2006 Page 4 through direct contact (dermal), and inhalation of vapors in while working in trenches in addition to the pathways shown on Fig. 6. The future commercial worker might be exposed by inhalation of indoor and ambient air vapors originating from ground water, too. Accordingly, an addendum to this HHRA addressing all potential groundwater pathways should be prepared after on-site groundwater data is collected. Alternatively, Geomatrix may collect soil-gas samples or use the NAPL version of the US EPA Johnson and Ettinger model-based spreadsheet. Future Land Use 4. Even though "The site is currently zoned for medium density residential(MDR)... (p. 8,par. 3), the risk assessment does not consider on-site residents. HHRA conclusions may be different under a residential land use scenario. Exposure Point Concentrations 5. Geomatrix prepared two sets of soil exposure point concentrations: 1) a surface soil set based on soil samples collected between 0 and 2 ft bgs, and 2) a subsurface soil set defined by soil samples collected between 0 and 10 ft bgs. According to p. 11, sections Surface Soil, and Surface and Subsurface Soil, the surface soil set was used to calculate the exposure of outdoor industrial workers through direct contact, and the surface and subsurface set to represent soil concentrations to which a construction worker may be exposed. The second set was also used to estimate potential exposure to chemicals in subsurface soil from inhalation of vapors in ambient and indoor air. Also, Geomatrix probably calculated the exposure, risk, and hazard from inhalation of particulates based on the first set data(no explanation was found in the text). This approach assumes no soil disturbance despite the fact that soil disturbance and placement of deeper soils on the surface is expected to occur during the construction activities (the construction worker is assumed to be exposed to soil between 0 and l Oft bgs). This would result in direct exposure of outdoor industrial worker to deeper soil contamination. Accordingly, I used the surface plus subsurface UCL concentrations presented in the table below in my modeling and exposure calculations. In the absence of the report calculations in electronic format, I compared the analytical soil data shown in Table 1 of the HHRA report to the data shown in the analytical laboratory reports provided in Appendix B of the Soil Investigation and Groundwater Monitoring Report. The following Table 1 inconsistencies were identified: • Benzo(a)anthracene at GMX-2-10 should read 0.073 mg/kg. • Benzo(k)fluoranthene at GMX-7-5 should read<0.130 mg/kg. • All PAHs at GMX-10-2 were non detects. However, the reporting limit should read< 0.025 mg/kg. • Benzo(g,h,i)perylene at GMX-12-2 should read 0.008 mg/kg. • Benzo(g,h,i)perylene at SP-1-1-2 should read 0.043 mg/kg, and pyrene<0.025 mg/kg.