SITE INFORMATION AND CORRESPONDENCE

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No Further Action Requiretermination - 2 - 30 September 2008 Mountain House DevelopmW Site #2 0 Source: Historical leak from crude oil pipeline(s) installed in the early 1900's and removed from service during the late 1960's and early 1970's. Actions: Preliminary investigations commenced in 2001. • In 2001, six exploratory borings were advanced and soil and groundwater samples were analyzed for TPH constituents of concern. Affected soil was noted in three samples from borings at depths ranging from 16 to 20 feet below ground surface (bgs). Analyses reported TPHc at concentrations of 640 milligrams per kilogram (mg/kg) in the sample from 16 feet bgs and 11 mg/kg and 12,000 mg/kg in two samples from 20 feet bgs. BTEX results were non-detect (ND) for these samples. PAHs were ND with exception of some PAHs detected at or slightly above the method detection limits (MDLs) in the sample raving a concentration of 12,000 mg/kg TPHc. Groundwater samples were not collected for analysis. • During 2004, an additional investigation included eight borings and collection of samples for analysis to further delineate affected soil and groundwater. TPHc concentrations detected in soil samples from depths between 2 and 27 feet bgs ranged from 530 mg/kg to 1,400 mg/kg. The remaining eight samples reported TPHc concentrations from ND for the majority of the samples to 98 mg/kg in a sample from 20 feet bgs. With exception of toluene at 0.2 mg/kg detected in a sample from 6 feet bgs, BTEX compounds were ND. Detection of PAHs at or slightly above the MDLs was reported in three samples from one boring. No BTEX or PAH constituent concentration exceeded respective ESLs for the construction/trench worker scenario. • In 2007, SAIC completed the ERE to evaluate exposure by comparing the analytical results to the 2005 ESLs for a construction/trench worker scenario. As noted above, TPHc, BTEX, and PAH constituent concentrations reported in samples taken in 2001 and 2004, did not exceed the ESLs. The highest detected concentration of TPHc, 12,000 mg/kg detected in a soil sample from the 2001 investigation, did not exceed the ESL of 15,000 mg/kg for a construction/trench worker scenario. Thus, SAIC concluded the TPHc concentrations and other TPH constituents detected do not pose a threat to human health for the construction/trench worker scenario. • In March 2008, 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 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 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 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.