ARCHIVED REPORTS_WELL ABANDONMENT, SOIL AND GROUNDWATER INVESTIGATION REPORT 2009

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MONITORING WELL DESTRUCTION AND SOIL AND GROUNDWATER INVESTIGATION REPORT US CAN—WELTY ROAD 1. INTRODUCTION Science Applications International Corporation (SAIC) prepared this report of monitoring well ' destruction and soil and groundwater investigation at the US Can-Welty Road site (the site) in Vernalis, California(Figure 1), at the request of Chevron Environmental Management Company (CEMC). The purpose of these activities was to eliminate monitoring wells that are no longer ! required, further evaluate the extent of soil and/or groundwater affected by the constituents of potential concern (COPCs), and recommend future site activities based on the results. The former Old Valley Pipeline (OVP) and Tidewater Associated Oil Company (TAOC) pipelines were crude-oil pipelines located at the site; these pipelines are managed in CEMC's Historical Pipeline Portfolio (HPP). As past site characterizations have documented the presence,but not the full extent, of petroleum hydrocarbons in soil and/or groundwater, CEMC wanted to further assess subsurface conditions. The COPCs for this site are total petroleum hydrocarbons (TPH) and polynuclear aromatic hydrocarbons (PAHs). Benzene, toluene, ethylbenzene, and total xylenes (BTEX) are minor constituents of crude oil; therefore, BTEX are also COPCs as they are ' sometimes encountered at former HPP facilities. SAIC performed this monitoring well destruction and soil and groundwater investigation in accordance with the 2007 work plan (SAIC, 2007) and the subsequent 2008 work plan addendum(addendum; SAIC, 2008). The work plan proposed the proper destruction of groundwater monitoring wells MW-3,MW-4, and MW-5, and an investigation to delineate the extent of soil and groundwater affected by crude oil. The California Regional Water Quality ! Control Board—Central Valley Region (RWQCB) accepted the work plan and addendum in letters dated October 11, 2007, and November 21, 2008 (RWQCB, 2007a and 2008a; see Appendix A). Well MW-3 did not meet the conditions under which the RWQCB would allow ! destruction, and therefore was not destroyed. Investigation decision making was guided by the Consistent Technical Approach (CTA) prepared by Geomatrix Consultants, Inc. (Geomatrix, 2005). The CTA specifies RWQCB Water Quality Objectives (WQOs; RWQCB, 2007b) as the health-based and aesthetic screening levels for determining whether groundwater is affected. Groundwater analytical results were also compared to the San Francisco Bay RWQCB Environmental Screening Levels (ESLs; RWQCB, 2008b). Under the California Water Code,WQOs are numerical or narrative limits for constituents or characteristics of water designed to protect beneficial uses of a body of groundwater or surface water. WQOs are found in the Water Quality Control Plan (Basin Plan; RWQCB, 2007b) adopted by the State and RWQCB. The Basin Plan lists WQOs in either numerical or narrative form. Where numerical objectives are listed, the values are enforceable limits. Where narrative objectives are listed, according to the Basin Plan they must be interpreted and a numerical limit selected to implement the narrative objective. Relevant water quality limits that may be used include drinking water standards, ambient water quality criteria, cancer risk estimates, health advisories and other numerical values that represent concentrations of chemicals that would limit specific uses of water (State Water Resources Control Board, 2008). For all HPP sites, including From Science to Solations !