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MONITORING WELL DESTRUCTION AND SOIL AND GROUNDWATER INVESTIGATION REPORT US CAN–WELTY ROAD 1. INTRODUCTION The Benham Companies, LLC, an SAIC Company(SAIC-Benham),prepared this report of monitoring well destruction and soil and groundwater investigation at US Can–Welty Road(the site; Figure 1) at the request of Chevron Environmental Management Company(CEMC). Former Old Valley Pipeline (OVP) and Tidewater Associated Oil Company(TAOC) crude-oil pipelines existed at the site. These two former pipeline systems are collectively referred to as CEMC's Historical Pipeline Portfolio–Bakersfield to Richmond(HPP-BTR). Past site investigations have documented the presence—but not the full extent—of HPP-BTR constituents in soil and/or groundwater, and CEMC wanted to further assess subsurface conditions. The purpose of this investigation was to evaluate the extent of soil and groundwater affected by the HPP-BTR constituents, and recommend future site activities based on the results. The scope of work included properly destroying three monitoring wells, advancing four soil borings at the site, and collecting soil and groundwater samples for analysis to further evaluate the lateral extent of affected media. SAIC-Benham performed this investigation in accordance with the scope of work proposed in a previous soil and groundwater investigation report(SAIC, 2009). The report and proposed scope were accepted by the Central Valley Regional Water Quality Control Board(RWQCB) in a January 2010 letter(Central Valley RWQCB, 2010a; Appendix A). Investigation decision making was guided by the Consistent Technical Approach(CTA) prepared by Geomatrix Consultants, Inc. (Geomatrix, 2005). The CTA specifies Central Valley RWQCB Water Quality Objectives (WQOs; Central Valley RWQCB, 2007) as screening levels for determining whether groundwater is affected. The CTA does not prescribe the criteria by which affected soil is delineated; therefore,to achieve alignment between soil and groundwater decision making, United States (U.S.)Environmental Protection Agency(EPA) Regional Screening Levels (RSLs; EPA, 2008)and San Francisco Bay RWQCB Environmental Screening Levels (ESLs; San Francisco Bay RWQCB, 2008) are used to evaluate soil laboratory analytical data. Appendix B provides a description of the use of screening levels and their derivation at HPP-BTR sites. The results of the field investigation event indicate that the extent of affected soil and groundwater at the site has been delineated. SAIC-Benham considers that no further investigation is warranted at the site and recommends the preparation of a risk assessment. 2. BACKGROUND 2.1 LOCATION AND SITE DESCRIPTION The site, which includes the area of investigation related to former HPP-BTR activities, is located southwest of the intersection of Highway 33 and S. Welty Road in Vernalis, San Joaquin County, California. It is situated at approximately 105 feet above mean sea level and has relatively flat topography that slopes gently downward to the northeast. The site is located in a 1ZZ The Benham Companies,LLC ..J Uj_ AW-11y ON+d S.b,6.,y From SCMnCe?a S0.v