SITE INFORMATION AND CORRESPONDENCE

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Chevron/UPRR - 2 - 12 June 2007 TAOC Tracy Pump Station RA Geomatrix comments/clarification: "For the vapor pathway to be complete, there must be: (1) a source of contamination, (2) a mechanism for transport of a substance from the source to indoor air, (3) a point where people come in contact with constituents in air, and (4) a route of entry into the body (i.e., breathing contaminated air). Under the most likely probable future site use, potential exposure to chemicals migrating from the subsurface into indoor air of structures also would not be complete because there are no current plans to construct any buildings at the site. Based on conversations with the City of Tracy, the Public Works Department would like to use the site for equipment storage. Because petroleum-related constituents would likely remain beneath the site once the site is graded and paved, a Site Management Plan (SMP) will be prepared to govern the long-term management of environmental conditions at the site relative to specific procedures and risk management measures, (e.g., no buildings without further subsurface characterization and assessment and/or installing appropriate engineering controls and adequate building ventilation to mitigate vapor intrusion concerns). The SMP also will be used to address potential exposures to volatile chemicals in groundwater if site redevelopment warrants intrusive activities down to the water table. Finally, the SMP also will be recorded in an Environmental Restriction. Because the vapor intrusion pathway is incomplete, Chevron and UPRR do not plan to collect soil vapor samples or conduct vapor intrusion modeling at this time." Regional Water Board response: Paving the site and not constructing buildings should preclude the vapor intrusion pathway. In addition, the SMP will provide guidance for future site owners/occupants and by recording an Environmental Restriction the subsurface conditions become part of the public notification record. 2. Regional Water Board comment: Removal or the soil piles may reduce%liminate potential health risk concerns at those locations. Geomatrix comments/clarification: "Although the removal of some crude oil-affected soil could reduce/eliminate potential health risks, the results of the health risk assessment, concurred by both the Water Board and OEHHA, demonstrate that constituents detected in soil do not pose a significant risk or hazard. The risk assessment is based on the premise that soil stockpiles will be distributed and graded across the site and that future receptors could potentially come in contact with this soil".