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SOIL AND GROUNDWATER INVESTIGATION <br /> VERNALIS OFFSITE <br /> 1. INTRODUCTION <br /> Science Applications International Corporation(SAIC)prepared this report of a soil and groundwater <br /> investigation at the off-site portion of the former Vernalis Pump Station in Vernalis,California(Vernalis <br /> ' Offsite; see Figure 1)at the request of Chevron Environmental Management Company(CEMC). The <br /> previous site investigation along with semi-annual groundwater monitoring and sampling documented <br /> total petroleum hydrocarbons (TPH)and polynuclear aromatic hydrocarbons(PAHs)in groundwater <br /> extending onto Vernalis Offsite. The Vernalis Pump Station was part of the former Old Valley Pipeline <br /> ' (OVP) system that transported heated crude oil. Benzene,toluene, ethylbenzene, and total xylenes <br /> (BTEX) are minor crude oil constituents; however,they have been encountered in soil and groundwater at <br /> the Vernalis Pump Station and therefore are also constituents of concern (COCs). The purpose of this site <br /> investigation was to further evaluate the extent of soil and groundwater affected by the COCs and <br /> recommend future assessment activities based on the results. <br /> SAIC documented the presence of the COCs in subsurface media in the Soil and Groundwater <br /> Investigation Report, Vernalis Pump Station, Vernalis, California(the SGIR; SAIC, 2006a). The SGIR <br /> concluded that the extent of affected soil and groundwater is delineated at Vernalis Pump Station but not <br /> off site. The Regional Water Quality Control Board(RWQCB) accepted the conclusions from the SGIR <br /> ' and made recommendations for additional off-site investigation in a letter dated September 20, 2006 <br /> (Appendix A). In a letter dated February 14, 2007,the RWQCB also agreed to divide the project into two <br /> sites to facilitate future investigations and reporting: Vernalis Pump Station and Vernalis Offsite. <br /> ' This investigation was also guided by the Technical Approach to Site Evaluation and Decision-Making, <br /> Historical Pipeline Portfolio, Central Valley Region (referred to as the Consistent Technical Approach <br /> [CTA])prepared by Geomatrix Consultants, Inc. (Geomatrix, 2005). The CTA specifies RWQCB Water <br /> ' Quality Objectives(WQOs) as the health-based and aesthetic criteria for determining whether <br /> groundwater is affected,delineating the extent of any affected groundwater,and assessing whether further <br /> groundwater characterization is appropriate. <br /> ' The CTA does not prescribe the criteria by which affected soil is delineated; therefore,the United States <br /> Environmental Protection Agency (EPA)Region 9 Preliminary Remediation Goals (PRGs; EPA, 2004) <br /> and San Francisco Bay RWQCB Environmental Screening Levels (ESLs; RWQCB, 2007) were used to <br /> ' evaluate laboratory analytical data. Soil and groundwater analytical results were also compared to ESLs, <br /> PRGs (soil), and WQOs (groundwater; RWQCB, 2004) as a screening step to streamline the risk <br /> assessment process. The presence of a COC at a concentration above a screening level does not <br /> ' necessarily indicate a risk to human health or the environment; it simply indicates that potential risk may <br /> exist, and additional evaluation may be warranted. COC concentrations below screening levels may <br /> qualify the site for No Further Action Required(NFAR) status. <br /> 2. BACKGROUND <br /> 2.1 LOCATION AND SITE DESCRIPTION <br /> ' The former Vernalis Pump Station is located at 35500 Welty Road,Vernalis, San Joaquin and Stanislaus <br /> counties, California(Figure 1). The former pump station primarily consists of two properties: the Bellini <br /> ' property (formerly known as the Roberts property), and the Arcos property (Figure 2). The Bellini <br /> property (San Joaquin Valley Assessor's Parcel Number[APN] 255-260-03) is a triangular-shaped, 5.73- <br /> acre vacant lot located on the northern part of the pump station site. The Arcos property(Stanislaus <br /> County APN 016-038-003) is an irregularly shaped parcel on the southern part of the former pump station <br /> site, and is currently used as a storage facility for equipment and materials; a residence and an on-site <br /> office are also on the property. <br /> ' 1Ma <br /> mmor\1%mss <br /> From Science to Solutions <br />