SITE INFORMATION AND CORRESPONDENCE

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No Further Action Required Deter ation - 3 - 5 May 2009 Mountain House Development Si4 and 2005, did not exceed applicable ESLs with one exception. The highest concentration of TPHc detected, 19,000 mg/kg in a 2001 soil sample, exceeds the ESL of 15,000 mg/kg for a construction/trench worker scenario. To further evaluate the TPHc concentrations relative to the ESL, a 95-percent upper confidence limit (UCL) was calculated for the TPHc data, using the United States Environmental Protection Agency software program called ProUCL. All TPHc data was evaluated using this program. According to the results, the calculated 95-percent ProUCL for highest TPHc concentration was 2,613 mg/kg, which is below the construction/trench worker ESL of 15,000 mg/kg. SAIC concluded the TPHc concentrations at the Site do not pose a threat to human health for the construction/trench worker scenario. • In September 2008, SAIL provided a No Further Action Required Request Report (NFAR) for consideration of Site closure. The NFAR included documentation of site 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 August 2008, 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 SMP 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 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 18 March 2009, Central Valley Water Board staff submitted notification to property owners and adjacent property owners that the Centraf Valley Water Board was considering a no further action determination for Mountain House Development Site #4 and that any comments to this action should be submitted within 30 days, i.e., by 20 April 2009. 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 1 to 16 feet bgs. The highest TPHc concentration was detected at a depth of 16 feet bgs. Threat to Groundwater: The historical OVP 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 slightly larger dimensions than the area of affected soil. Crude oil affected groundwater has been defined beneath the highway within the highway ROW easement. There were no existing water wells identified within one-half mile of the area of affected groundwater. Considering the Site is located within the highway ROW easement, the installation of wells is not anticipated.