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Chevron Environmental Management Company Soil and Groundwater Investigation Report Tracy Byron Road Project of trenching along the Byron Road corridor. This evaluation was included in the background section of the Workplan. Following an in-depth review of the above information sources, SAIC developed a conceptual site model of residual petroleum beneath the site and its known characteristics in the subsurface. Based on the properties(or characteristics) of the known contaminant, apparent data gaps identified in the vicinity of several rural properties adjacent to Byron Road, and RWQCB concerns along the corridor, a project scope of work was prepared. SAIC's proposed scope of work focused on primary assessment borings to be located in the City of Tracy Right of Way(ROW)with respect to several rural properties adjacent to the Byron Road corridor. The primary assessment borings were installed to characterize the lateral and vertical extent of petroleum- affected soil and groundwater in the vicinity of these rural properties. The RWQCB approved the Workplan in a letter dated September 8, 2003. The RWQCB requested information regarding off-site soil and groundwater conditions in the vicinity of Caldron's General Store, if available. If not available,the RWQCB requested an additional boring be placed adjacent to Caldron's property boundary in the City of Tracy's ROW. The RWQCB recommended additional soil borings be placed in the vicinity of borings B-10,B-14, and B-15 advanced as part of a Pacific Gas and Electric (PG&E) environmental investigation. The PG&E investigation extended northwest from approximately Bel Conte Drive to the border of the former McCormack property next to SAIC's borings SB-34 and SB-35 (ECM Group, 2003). Furthermore, as part of potential human health concerns,the RWQCB also recommended the sampling of private water supply wells identified in SAIC's well search conducted on June 26,2003. SAIC performed the preliminary assessment borings in the vicinity of the above-mentioned rural properties in accordance with the Second Draft Revised Technical Approach to Site Evaluation and Decision Making; Old Valley Pipeline Sites(CTA, 2002), and the approved Workplan. A copy of the RWQCB letter dated September 8, 2003 is included in Appendix A. 2. SITE DESCRIPTION The TBRP study area encompasses an approximate 7,000-foot long corridor along the south side of West Byron Road in Tracy, California. The corridor trends from northwest near the intersection of West Byron Road and Von Sosten Road, to southeast near the intersection of West Byron Road and Belconte Drive (Figure 2A and 2B). Currently, West Byron Road mainly serves residential properties and small businesses located to the north or to the south of the road. The study area contains the former Standard Oil of California Wait-Mendota-Richmond Pipeline (OVP) right of way(ROW) and Tidewater Associated Oil Company(TAOC)Pipeline ROW. The OVP was operated as a hot oil line from 1903 until the early to mid 1930s. The OVP lines north of Tracy were operated until the late 1960s. The TAOC pipeline system was constructed in 1907 and also operated as a hot oil line until the 1970s. The former old valley pipelines (hereinafter, OVP shall collectively refer to the OVP and TAOC pipelines unless otherwise stated)carried heated crude oil and Bunker C fuel oil. The OVP pipeline ROW extends to the south side of West Byron Road and the TAOC pipeline ROW is on the north side of West Byron Road in the Union Pacific Railroad(UPRR)ROW. 2.1 GEOLOGY AND HYDROGEOLOGY Regionally,the study area is encompassed within the Tracy Sub-basin(Groundwater Basin Number 5-22.15) and is defined by the aerial extent of unconsolidated to semi-consolidated sedimentary deposits that are bounded by the Diablo Range on the west,the Mokelumne and San Joaquin Rivers on the north, the San Joaquin River to the east, and the San Joaquin-Stanislaus County line on the south. The Tracy Sub-basin is located adjacent to the eastern San Joaquin Sub-basin on the east and the Delta-Mendota Sub-basin on the south(DWR,Revised Draft Bulletin 118). The above-mentioned sub-basins are located within the larger San Joaquin Valley Groundwater Basin. The Tracy Sub-basin is comprised of continental deposits of Late Tertiary to Quaternary age, which include the Tulare Formation, Older Alluvium,Flood Basin Deposits, and Younger Alluvium. The thickness of these formations ranges from a few hundred feet in the western foothills to about 3,000 feet 2