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SUPPLEMENTAL GROUNDWATER INVESTIGATION AND GEOMATRIX RECOMMENDATION FOR SITE CLOSURE Surland Homes Property Tracy, California 1.0 INTRODUCTION ' This report was prepared by Geomatrix Consultants, Inc. (Geomatrix), on behalf of Chevron Pipe Line Company(CPL),to present the results of a supplemental groundwater investigation performed by Geomatrix and our recommendation for site closure of the Surland Homes ' Property in Tracy, California(Figure 1). The purpose of the investigation was to gather data to evaluate whether groundwater at the site is affected by residual petroleum hydrocarbons. The work was performed in accordance with CPL'S 26 August 1998 work plan which was submitted to, and approved by, the San Joaquin County Public Health Services(SJCPHS). Background information, a summary of the investigation activities, a summary of results, and our conclusions and recommendations are presented below. Additionally, site conditions are compared to conditions at an adjacent CPL site(Dividend Property) and available regulatory 1 guidance in support of site closure. 2.0 BACKGROUND ' CPL's former Old Valley Pipeline(OVP)was located in a right-of-way along the southwest edge of the site. The former OVP transported heavy petroleum(crude and fuel oil) from Bakersfield to Richmond, California, from the early 1900s to the 1950s. 2.1 PREVIOUS ON-SITE SOIL AND GROUNDWATER INVESTIGATIONS ' Geomatrix performed a soil and groundwater investigation at the site on 8 July 1998 to assess the possible presence of petroleum hydrocarbons in the subsurface as a result of the former OVP. The work was performed using the approach outlined in the "Technical Approach to Site Evaluation and Decision Making, Old Valley Pipelines Sites, Central Valley Region" (Technical Approach), approved by the California Regional Water Quality Control Board—Central Valley Region(RWQCB) in March 1997 (Geomatrix, 1997),which is designed ' \\sf3\deptdata\Doc_Safe\4780.01\clsrrpcdoc 1