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Scott Mansholt - 3 - • 21 November 2007 <br /> TAOC Tracy Pump Station <br /> Review of the data indicates that residual petroleum hydrocarbons in soil at the site do not <br /> result in a significant source of TPH constituents to groundwater. The City of Tracy Municipal <br /> Code for administrative reasons unrelated to petroleum impacts prohibits the use of shallow <br /> groundwater wells for domestic or municipal use. Domestic and municipal water services are <br /> provided by the City of Tracy; use of shallow groundwater at the property is unlikely to occur. <br /> Human Health Risk Assessment <br /> A Human Health Risk Assessment (HHRA), by Geomatrix, dated 30 June 2005, was <br /> submitted to OEHHA to assess the potential risk and health hazard presented by conditions at <br /> the site. The HHRA was conducted based on a residential use scenario, which is the most <br /> conservative approach for evaluating risk. <br /> According to the HHRA..."the total estimated hazard index for a future commercial worker is <br /> 0.04 and the total estimated excess lifetime cancer risk is 8x10-8. The total estimated hazard <br /> index for a construction worker is 0.002 and the total estimated cancer risk is 7x10-7. The <br /> total estimated hazard index for off-site residents is 3x10-8 and the total estimated cancer risk <br /> is 7x10-10." Further, the HHRA determined ..."the cumulative excess lifetime cancer risks for <br /> these receptors do not exceed the target level of 1 x105 for workers or 1 x10-6 for offsite <br /> residents and the cumulative long-term non-cancer health effects do not exceed a target HI <br /> (hazard index) of 1 .0." <br /> OEHHA's staff toxicologist provided review comments to Regional Water Board staff in a <br /> 13 October 2006 letter, which concluded: <br /> "The performed recalculation demonstrated that no significant risk/hazard is expected to <br /> occur due to the PAH soil contamination down to 10 feet bgs. Soil contamination below <br /> 10 feet bgs and groundwater contamination were not addressed in this risk <br /> assessment." <br /> OEHHA staff determined that risk at the site, based on the Risk Assessment data, is <br /> acceptable provided the land use remains as commercial/industrial. Chevron previously <br /> informed Regional Water Board staff that the future site use would be commercial/industrial. <br /> Subsequently, Regional Water Board staff reviewed OEHHA's summary report and provided <br /> comments to Chevron in a letter dated 16 January 2007. Our review concurred with OEHHA's <br /> findings but requested clarification and comment for the following: <br /> • 1) Collect and submit soil-gas samples for analysis or use the US EPA Johnson & <br /> Ettinger model spread sheet to estimate concentrations of TPH vapors potentially <br /> originating from groundwater as a pathway. <br /> Geomatrix response: ...the vapor intrusion pathway is incomplete because there are no <br /> existing on-site structures; and most likely based on probable future site use, the <br /> potential exposure to chemicals migrating from the subsurface into indoor air of <br /> structures would not be complete as there are no plans to construct buildings at the <br /> site...and petroleum-related constituents would likely remain beneath the site once the <br />