SITE INFORMATION AND CORRESPONDENCE

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Chevron - Michael Oliphant _ 3 19 January 2012 NFAR - Mountain Nouse Development Site#6 • SAIC completed an HHSE in January 2011 and evaluated analytical results of samples in accordance with DTSC's PEA Guidance Manual for a hypothetical future onsite resident as the most conservative estimate of risk for the Site. In conjunction, the cancer and non-cancer toxicity values promulgated by the California Office of Environmental Health and Hazard Assessment (OEHHA) were considered to quantitatively estimate potential risk and hazard. The HHSE also included an evaluation of risk to future construction maintenance workers. In accordance with the PEA guidance, the HHSE considered analytical results for BTEX and certain PAH compounds present, if any. Laboratory results of 49 soil samples from 38 borings at depths of between 0 and 10 feet bgs were used. The HHSE found that the onsite cancer risk and non-cancer hazard are below the respective de minimus levels considered protective of human health. SAIC concluded the TPHc and related TPH compounds detected should not result in an unacceptable health risk for an adult or child onsite resident or for a construction/maintenance trench worker, considered the likely risk scenario. • In September 2011, SAIC provided a No Further Action Required Request Report (NEAR) for consideration of Site closure. The NFAR included documentation of Site conditions in accordance with the April 2004 Appendix A — Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Storage Tank Sites, Section 6.5 NFAR for Cases Exceeding Water Quality Objectives. • A site-specific Soil and Groundwater Management Plan (SGMP) submitted 15 September 2011, describes procedures to follow and contains the contact names and phone numbers for representatives of Chevron and the San Joaquin County Environmental Health Department if future activities encounter crude oil affected soil. The SGMP serves as a guideline for Chevron to implement for the handling, reuse, and disposal of any crude oil-affected soil and/or groundwater that may be encountered or excavated at the Site in the future. The SGMP provides procedures for Site property owners, developers, and/or maintenance firms to follow that addresses such topics as trench excavations, dewatering, and health and safety guidelines. + On 14 October 2011, Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff provided notification to property owners and adjacent property owners that the Central Valley Water Board was considering a no further action determination for Mountain House Development Site #6. No responses were received during the 30 day comment period. Extent defined: Yes. Estimated Residual Petroleum Mass: Unknown; petroleum occurs primarily as degraded TPHc (immobile petroleum hydrocarbon fractions) at approximate depths of 2 to 26 feet bgs. A small volume of separate phase crude oil noted at approximately four to six feet bgs was projected next to/beneath West Byron Road. Threat to Groundwater: The historical pipelines, considered the source of the crude oil leaks, were removed from service approximately 35 or more years ago. The extent of affected groundwater has been defined beneath/within the highway easement, under the active pipeline easement, part of the railroad tracks, and the downgradient under adjacent agricultural fields, primarily to the northeast. Since the Site is described within a highway/pipeline/UPRR easements, utility corridor and beneath agricultural fields, it is not likely that installation of drinking water wells would be considered in the future. Review of Department of Water Resources records, indicated five existing water wells within a 2,000 feet