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Lee Higgins -3- 19 May 2011 ' <br /> Mountain House Development Site#6 <br /> • The total potential non-cancer hazard from oral, dermal, and inhalation exposures to ' <br /> onsite soils was determined to be 0.002, well below the hazard index of 1, and indicates <br /> an acceptable non-cancer health hazard exposure to onsite soils for hypothetical future <br /> residents. , <br /> • Results of the HHSE indicate that exposure to chemicals present at the Site should not <br /> result in an unacceptable health risk for an onsite resident. SAIC concluded that no ' <br /> remedial action is necessary for protection of human health and that a risk <br /> management decision for no further action could be made. <br /> • As part of the HHSE, a feasibility evaluation of potential technology options previously <br /> conducted was reviewed for addressing weathered crude oil found at the Site. SAIC , <br /> concluded that in-place management/monitored natural attenuation was the most <br /> feasible and cost effective process for the Site given the hydrocarbons present in soil <br /> and groundwater are immobile and have been defined generally beneath the highway, ' <br /> active pipeline corridor, railroad tracks, and an adjacent agricultural field <br /> • SAIC queried the 2010 California Natural Diversity Database, maintained by the ' <br /> California Department of Fish and Game, to search for threatened, endangered, or <br /> sensitive species in the vicinity of the Site. The assessment indicates that a threat to <br /> sensitive ecological receptors does not appear to exist. , <br /> Based on the review, Central Valley Water Board staff has the following comments: <br /> • A conservative approach utilizing a residential scenario for a hypothetical future ' <br /> resident was considered in the HHSE. However, the Site is anticipated for continued <br /> use as part of the highway, railroad, active pipelines, and for agricultural purposes. <br /> Central Valley Water Board staff concur with the findings of the HHSE and related <br /> supporting documentation. The Site is a candidate for closure under the conditions <br /> evaluated. A request for a No Further Action Required (NFAR) determination may be ' <br /> prepared. <br /> • Documentation to support a NFAR closure determination should be completed in <br /> accordance with the California Regional Water Quality Control Board Central Valley ' <br /> Region's 16 April 2004 update to Appendix A of the Tri-Regional Board Staff <br /> Recommendations for Preliminary Investigation and Evaluation of Underground Tank <br /> Sites - No Further Action Requests. Section 6.5 - NFAR for Cases Exceeding Water ' <br /> Quality Objectives should be followed for documenting Site conditions. <br /> • Consistent with other Chevron OUP sites, a Soil and Groundwater Management Plan <br /> (SGMP) needs to be submitted. <br /> 1 <br />