SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt - 4 - 4 April 2008 Mountain House Site #2 soil at the site do not result in a significant source of TPH constituents to groundwater; and, the groundwater plume is limited in extent and slightly larger than the area of affected soil. Regional Water Board staff concurs with the summary provided in the Request for No Further Action at the Mountain House Site #2 project and that it appears the site is a candidate for closure based on the following: • The extent of affected soil and groundwater have been adequately delineated and residual petroleum hydrocarbons remaining at the site will continue to decrease over time by natural attenuation; • Mountain House Site #2 lies within the Byron Road public roadway ROW easement and the affected soil and groundwater lie beneath Byron Road and the former OVP lines; remedial alternative studies by SAIC indicated that, since the majority of affected soil and groundwater lie beneath Byron Road and the OVP lines, it is not feasible or practical to conduct excavation activities; • It is likely that future site activities will be limited to construction/trench workers within the public easement ROW; an environmental risk evaluation demonstrated that residual TPHc does not pose a health risk for future construction/trench worker(s); and, • In accordance with SWRCB Resolution No. 92-49, SAIC has demonstrated that readily available alternative remedial options are infeasible, very costly, and that natural attenuation is the most practical and viable option for the site. If existing, additional, or previously unidentified chemical constituents at the site cause or threaten to cause pollution or nuisance or are found to pose a threat to public health or water quality, then 1) nothing in this determination is intended or shall be construed to limit or preclude the Regional Water Board or any other agency from taking any further enforcement action, and 2) this letter does not relieve Chevron of any responsibilities mandated under the California Health and Safety Code and the California Water Code. By 1 July 2008, please provide the Soil Management Plan (SMP) for the site. The SMP serves as a guideline for Chevron to implement for the handling, reuse, and disposal of any soil affected by the degraded crude oil that may be encountered or excavated during site activities. The SMP outlines detailed procedures for future property owners, developers, and/or maintenance firms to follow addressing such topics as dewatering from excavations, health and safety guidelines, and includes contact telephone numbers for Chevron and San Joaquin County Environmental Health Department.