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Michael N. Oliphant -2- 25 May 2011 <br /> Chevron <br /> Former Vernalis Pump Station <br /> threshold lifetime de minimus cancer risk of 1 E-06. This value indicates an acceptable cancer <br /> risk for exposure to onsite soils for a hypothetical future resident under those Site conditions <br /> evaluated. <br /> Additionally, the future potential non-cancer health hazards from direct contact and indirect <br /> inhalation exposure to onsite soils, and the non-cancer hazards for individual chemicals of <br /> potential concern (COPCs), were estimated. The results were summed and the aggregate <br /> non-cancer health hazard for oral, dermal, and inhalation exposure to onsite soils and non- <br /> cancer hazards from subsurface vapor intrusion was estimated to be 3E-03, which is well <br /> below the acceptable non-cancer hazard index of 1. <br /> The California Natural Diversity Database, 2009, maintained by California Department of Fish <br /> and Game, reviewed by SAIC, indicated that sensitive ecological receptors do not appear to <br /> exist within one mile of the Site. Current and future land use is unlikely to provide suitable <br /> habitat. <br /> The shallow background water quality at the Site exceeds State and Federal standards for <br /> total dissolved solids (TDS) for drinking water and some agricultural purposes. SAIC <br /> concluded the shallow Site groundwater is not likely to be used as a drinking water source, <br /> and that alternative good quality water supply sources are available nearby. Thus, the direct <br /> exposure pathway was considered incomplete and the HHSE did not quantitatively evaluate <br /> that pathway. Five groundwater monitoring wells associated with the Site were destroyed in <br /> May 2009 in accordance with the respective County guidelines. <br /> Findings provided in SAIC's reports indicate the extent of TPH in soil is delineated as having <br /> approximate dimensions measuring 275 feet by 750 feet, generally parallel to the OVP/TAOC <br /> pipeline alignments at, and along the east side of the Site. Crude oil affected groundwater has <br /> been defined onsite and upgradient, and laterally crossgradient to the east-northeast of the <br /> Site at the Vernalis Offsite project. An NFAR determination for the Vernalis Offsite project was <br /> issued to Chevron 8 June 2010. <br /> In a December 2010 letter, Central Valley Water Board staff notified Chevron that crude oil <br /> affected soil and groundwater had been delineated, and additional characterization was not <br /> needed. Based on the findings, Central Valley Water Board staff concurred that the Site was <br /> a candidate for closure and a request of no further action could be prepared. <br /> Previously, SAIC assessed available cleanup technologies and various remedial alternatives <br /> for residual crude oil in soil and groundwater at OVP/TAOC projects. The assessment <br /> summarized that the residual weathered crude oil is highly viscous, relatively immobile, and <br /> primarily occurs within low permeability soil found at the Site. SAIC concluded that affected <br /> soil/groundwater has been delineated and in-place management of residual crude oil by <br /> natural attenuation is cost effective, feasible, and easily implemented. Concentrations of <br /> residual petroleum hydrocarbons will reduce with time. <br /> Based on the alternative cleanup technological assessment and consistent with State Water <br /> Resources Control Board Resolution No. 92-049, SAIC concluded there is no known feasible <br /> cost effective means, or easily implemented process to effectively remove the petroleum <br />