ARCHIVED REPORTS_SOIL AND GROUNDWATER INVESTIGATION WORK PLAN

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' SOIL AND GROUNDWATER INVESTIGATION WORK PLAN VERNALIS OFFSITE ' 1. INTRODUCTION At the request of Chevron Environmental Management Company(CEMC), Science Applications ' International Corporation(SAIC)presents this work plan for additional investigation on the Bogetti property in Vernalis, California(Figure 1). The previous site investigation documented total petroleum hydrocarbons(TPH)and polynuclear aromatic hydrocarbons(PAHs)in groundwater extending onto the ' Bogetti property from the former Vernalis Pump Station,which was part of the former Old Valley Pipeline (OVP)system that transported heated crude oil. Although benzene,toluene, ethylbenzene, and xylenes(BTEX)are minor crude oil constituents,they are also constituents of concern(COCs)because they have been encountered in soil and groundwater at the Vernalis Pump Station. As the off-site extent ' of petroleum-affected groundwater is not delineated, CEMC wants to further assess subsurface conditions. ' Most recently, SAIC documented the presence of the COCs in subsurface media in the Soil and Groundwater Investigation Report, Vernalis Pump Station, Vernalis, California(the SGIR; SAIC, 2006a). In the SGIR, SAIC concluded that the extent of affected soil and groundwater is delineated at Vernalis Pump Station but not off site on the Bogetti property. In a letter dated September 20, 2006,the ' Regional Water Quality Control Board(RWQCB)accepted the conclusions and recommendations for additional investigation on the Bogetti property(Appendix A). To facilitate future investigations and reporting, the RWQCB also agreed, in a letter dated February 14, 2007,to divide the project into two ' sites: Vernalis Pump Station and Vernalis Offsite. An investigation to evaluate the extent of affected groundwater off site on the Bogetti property will be performed in accordance with this work plan. This investigation will also be 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]; Geomatrix Consultants,Inc. [Geomatrix], 2005). The CTA specifies RWQCB Water Quality Objectives(WQOs)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. Although the CTA does not prescribe the criteria by which affected soil is defined,U.S.Environmental ' Protection Agency(EPA)Region 9 Preliminary Remediation Goals(PRGs;EPA,2004)and San Francisco Bay RWQCB Environmental Screening Levels(ESLs;RWQCB,2005)will be used. Analytical results will also be compared to ESLs,PRGs(soil), and WQOs(groundwater)as a screening ' step to streamline the risk assessment process. The presence of a constituent at a concentration above a screening level does not necessarily indicate an impact to human health or the environment. It simply indicates that a potential for risk may exist and that additional evaluation may be warranted. Based on ' comparison of analytical results to the screening levels, the Bogetti property may qualify for No Further Action status. 2. BACKGROUND 2.1 LOCATION AND SITE DESCRIPTION ' The former Vernalis Pump Station is located at 35500 Welty Road,Vernalis, San Joaquin and Stanislaus counties, California(Figure 1). The former pump station primarily consists of two properties: the Bellini property(formerly known as the Roberts property) and the Arcos property(Figure 2). The Bellini property is a triangular-shaped, 5.73-acre vacant lot located on the northern part of the pump station site. ' The Arcos property is an irregularly shaped parcel on the southern part of the former pump station site, which is currently used as a storage facility for equipment and materials; a residence and an on-site office 1 aa—Z_ as _= ..WA.. ' From Science to Solutions