SITE INFORMATION AND CORRESPONDENCE

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No Further Action Required leermination - 3 - • 25 September 2008 Mountain House Development Site #1 conditions in accordance with the 16 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 Management Plan (SMP) submitted in June 2008 describes procedures to follow, and contains the contact names and phone numbers for representatives of Chevron and the San Joaquin County Health Department if future activities encounter crude oil-affected soil. The SMP serves as a guideline for Chevron to implement for the handling, reuse, and disposal of any crude oil-affected soil that may be encountered or excavated at the Site in the future. The SMP 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. Contact telephone numbers for Chevron and San Joaquin County Environmental Health Department are included. • On 1 August 2008, Central Valley Water Board staff submitted notification to property owners and adjacent property owners that the water board was considering a no further action determination for Mountain House Site #1 and that any comments to this action should be submitted within 30 days. No comments were received. Extent defined: Yes. Estimated Residual Petroleum Mass: Unknown. Petroleum occurs primarily as degraded TPHc (immobile petroleum hydrocarbon fractions) at depths of approximately 2 to 36 feet. The highest TPHc concentrations were detected at depths of 9 to 36 feet bgs. Threat to Groundwater: The historical pipelines, the source of the crude oil leaks, were removed from service approximately 35 or more years ago. The lateral and vertical extent of affected groundwater is limited having the same approximate dimensions as the area of affected soil. Affected groundwater has been defined beneath the highway, railroad tracks, and two active pipelines. Existing water wells are located more than 1/4 mile of the area of affected groundwater. Review of the Department of Water Resources records indicate that the surface seals of these wells extend below the depth of affected groundwater. It is not anticipated these wells will be affected by the crude oil. Considering the site is located within the utility corridor, the installation of new water wells is not anticipated. Threat to Human Health: • Vapor intrusion hazard: there is no vapor intrusion pathway. • Dermal contact hazard: future maintenance excavation within the ROWs is possible. Consequently, the applicable ESLs are for a construction/trench worker scenario. The concentrations of residual crude oil are below health protection ESLs for construction/trench workers. The site is located within the West Byron Road and UPRR ROWs and usage for these features is not expected to change reducing/minimizing potential human contact with TPH compounds remaining at the site.