ARCHIVED REPORTS SOIL AND GROUNDWATER INVESTIGATION REPORT

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SOIL AND GROUNDWATER INVESTIGATION REPORT TRACY BYRON ROAD PROJECT ' 1. INTRODUCTION Science Applications International Corporation (SAIC)prepared this report of a soil and groundwater investigation at the Tracy Byron Road project site(the site; Figure 1) at the request of Chevron ' Environmental Management Company (CEMC). Past site investigations documented the presence,but not the full extent, of total petroleum hydrocarbons(TPH) and polynuclear aromatic hydrocarbons (PAHs) in soil and groundwater in the vicinity of former crude-oil facilities of Chevron's Old Valley Pipeline(OVP)and the Tidewater Associated Oil Company (TAOC). Benzene,toluene,ethylbenzene, and total xylenes(BTEX) were minor constituents of crude oil,but they are also constituents of concern (COCs) as they are sometimes encountered at OVP and TAOC facilities. The purpose of this site ' investigation was to further evaluate the extent of soil and groundwater affected by the COCs and recommend future assessment activities based on the results. The initial work plan for this investigation was submitted to the Central Valley Regional Water Quality Control Board(RWQCB) in July 2004 and accepted in a September 2004 letter to Chevron (RWQCB, 2004c; Appendix A). SAIC updated and submitted a revised work plan to the RWQCB in February 2007 (SAIC, 2007), after new methods were developed for Chevron's Historical Pipeline Portfolio (HPP) ' investigations (e.g.,collecting groundwater samples using pre-packed well screens, testing for General Minerals,etc). Investigation startup was deferred until access was gained to five of the nine proposed borings in March 2007. ' This investigation was also guided by the Technical Approach to Site Evaluation and Decision-Making, Historical Pipeline Portfolio, Central Valley Region(referred to as the Consistent Technical Approach [CTA])prepared by Geomatrix Consultants,Inc. (Geomatrix, 2005). The CTA specifies RWQCB Water ' Quality Objectives (WQOs; RWQCB, 2004b)as the health-based and aesthetic criteria for determining whether groundwater is affected,delineating the extent of any affected groundwater, and assessing whether further groundwater characterization is appropriate. U.S.Environmental Protection Agency (EPA) Region 9 Preliminary Remediation Goals(PRGs; EPA, 2004) and San Francisco Bay RWQCB Environmental Screening Levels (ESLs; RWQCB, 2007) were used to evaluate soil analytical data because the CTA does not prescribe the criteria by which affected soil is delineated. ' Soil and groundwater analytical results were also compared to ESLs,PRGs, and WQOs as a screening step to streamline the risk assessment process. The presence of a COC at a concentration above a screening level does not necessarily indicate a risk to human health or the environment; it simply ' indicates a potential risk,and that additional evaluation may be warranted. COC concentrations below screening levels may qualify the site for No Further Action Required(NFAR) status. ' 2. BACKGROUND 2.1 LOCATION AND SITE DESCRIPTION The project area encompasses an approximately 7,000 foot-long corridor along West Byron Road in Tracy, California. The work completed during this investigation was conducted at the western end of the West Byron Road corridor near the intersection of South Lammers Road and West Byron Road (Figures 2a through 2f). The corridor trends from the northwest near the intersection of West Byron Road and ' Von Sosten Road,to the southeast near the intersection of West Byron Road and North Corral Hollow Road. West Byron Road mainly serves residential properties and small businesses located to the north or to the south of the road (SAIC, 2004a). The study area is approximately 35 feet above mean sea level ' (MSL)and has relatively flat-lying topography. From Science to Solutions