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SOIL AND GROUNDWATER INVESTIGATION REPORT <br /> MOUNTAIN HOUSE DEVELOPMENT SITE #6 <br /> 1. INTRODUCTION <br /> The Benham Companies, LLC, an SAIC Company(SAIC-Benham)prepared this report of a soil <br /> and groundwater investigation at Mountain House Development Site #6 (the site; Figure 1) at the <br /> request of Chevron Environmental Management Company(CEMC). Former Old Valley <br /> Pipeline (OVP) and Tidewater Associated Oil Company(TAOC) crude-oil pipelines existed on <br /> the site. These two former pipeline systems are collectively referred to as the CEMC Historical <br /> Pipeline Portfolio—Bakersfield to Richmond(HPP-BTR). The constituents analyzed at HPP- <br /> BTR sites are total petroleum hydrocarbons (TPH); benzene, toluene, ethylbenzene, and total <br /> xylenes (BTEX); and polynuclear aromatic hydrocarbons (PAHs). Hydrocarbons associated <br /> with the HPP-BTR are typically highly weathered, and BTEX compounds are rarely present. <br /> TPH analysis and fuel fingerprinting are commonly used to distinguish HPP-BTR related <br /> petroleum hydrocarbons from other sources. <br /> Past site investigations documented the presence, but not the full extent, of petroleum <br /> hydrocarbons in soil and groundwater, and CEMC wanted to further assess subsurface <br /> conditions. The purpose of this investigation was to evaluate the extent of soil and groundwater <br /> affected by the crude-oil constituents and recommend future site activities based on the results. <br /> SAIC-Benham performed this investigation in accordance with the scope of work proposed in <br /> the July 2008 soil and groundwater investigation report (SGIR; SAIC, 2008). The report was <br /> accepted by the Central Valley Regional Water Quality Control Board (RWQCB) in a November <br /> 2008 letter(RWQCB, 2008a). The RWQCB requested implementation of the scope of work as <br /> well as an additional boring. A work plan addendum(SAIC, 2009) was submitted to and <br /> subsequently accepted by the RWQCB (RWQCB, 2009). The regulatory correspondence is <br /> included in Appendix A. <br /> Investigation decision making was guided by the Consistent Technical Approach(CTA) <br /> prepared by Geomatrix Consultants, Inc. (Geomatrix, 2005). The CTA specifies Central Valley <br /> RWQCB Water Quality Objectives (WQOs; RWQCB, 2007a) as screening levels for <br /> determining whether groundwater is affected. <br /> WQOs are defined in the Water Quality Control Plan (Basin Plan; RWQCB, 2007b). The Basin <br /> Plan notes that WQOs exist in either numerical or narrative form. Where numerical limits do not <br /> exist, a numerical limit interpreting the narrative WQO is available in the RWQCB water quality <br /> goals document(State Water Resources Control Board, 2008). For delineation purposes at all <br /> HPP-BTR sites, including the subject of this report, the WQO for each constituent is the lowest, <br /> most conservative published numerical value. <br /> In addition to WQOs, the San Francisco Bay RWQCB Environmental Screening Levels (ESLs; <br /> RWQCB, 2008b), which were not available at the time of the CTA development, have been <br /> added as an additional screening tool for delineation decision making. <br /> The CTA does not prescribe the criteria by which affected soil is delineated; accordingly, for <br /> alignment between soil and groundwater decision making, United States (U.S.) Environmental <br /> Protection Agency(EPA) Regional Screening Levels (RSLs; EPA, 2008a) and RWQCB ESLs <br /> are used to evaluate soil laboratory analytical data. <br /> 1 <br /> Fmin Science to Solutions <br />