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Chevron Environmental Management Company Soil and Groundwater Investigation Report Tracy Byron Road Project near the eastern margin of the basin(DWR,Bulletin 118). The Tulare Formation is comprised of semi- consolidated,poorly sorted, discontinuous deposits of clay, silt, and gravel. The Corcoran clay is situated near the top of the Tulare Formation, separating groundwater in the basin in what has been reported as two primary aquifers. The upper aquifer is reported to range in thickness from 15 to 250 feet bgs and the lower aquifer is reported at a depth of 600 feet bgs. Generally, depth to groundwater in the Tracy Sub- basin varies from 5 to 10 feet bgs. Locally,the study area is situated at an approximate elevation of 35 feet above mean sea level (MSL) and topographically is relatively flat lying. Groundwater in the upper water-bearing zone flows in a northerly direction and is hydraulically controlled by low-permeable unconsolidated sediments. Soils encountered appear to be fine-grained unconsolidated sediments, consisting mainly of silts and clays with minor amounts of poorly graded sand and gravel. Typical soil observed in a boring from the west end of the study area,north of Byron Road, consisted of silty clay(CL) from ground surface to an approximate depth of 15.5 feet bgs, overlying a lens of poorly graded sand(SP)from approximately 15.5 feet to 16 feet bgs, overlying a silty clay(CL)to a total depth of 16.5 feet bgs. Typical soil observed in a boring from the east end of the study area, south of Byron Road consisted of silt(ML) from ground surface to approximately 2.5 feet bgs,underlain by silty clay(CL) from 2.5 feet to a total depth of 25 feet bgs. 3. PREVIOUS ENVIRONMENTAL WORK Several private properties have undergone soil and groundwater investigations to facilitate development adjacent to the West Byron Road corridor and the former pipeline ROW. These properties include: the Cintra Property, the Dividend Property, the Dobler Property,the Filios/Mansfield Property, the McCormack Property, the Monterosso Property, the Nicholaw/Souza, and the Surland Homes Property. SAIC presented a historical review of these properties and past environmental investigations in SAIC's Workplan dated August 18, 2003. As a result of past investigations,the RWQCB and/or the SJCEHD issued"No Further Action"letters for the referenced properties, except for the Surland Homes Property. The Surland Homes Property continues to be evaluated for closure. Additional historical details can be found in SAIC's Workplan(August 2003). 4. FIELD ACTIVITIES 4.1 PRE-FIELD GOALS The Workplan identified areas along the former OVP ROW where data gaps existed. These data gaps included the agricultural property west of Interstate 205, and the rural properties located adjacent to the City of Tracy's ROW along West Byron Road. The Workplan proposed the installation of seven soil borings on 200-foot centers adjacent to the agricultural land west of Interstate 205 to evaluate the lateral and vertical extent of petroleum-affected soil and groundwater along this portion of West Byron Road. The Workplan also proposed at least one soil boring in front of each rural property placed on approximately 150-foot centers in the City of Tracy ROW east of Interstate 205, including soil borings in the vicinity of Caldron's General Store and in the vicinity of former borings SB-10, SB-14, and SB-15 advanced during the PG&E March 2003 investigation. These borings were placed to evaluate the lateral and vertical extent of petroleum-affected soil and groundwater east of Interstate 205. Additional data gaps identified in the Workplan included the absence of groundwater analytical data from several water supply wells identified at the rural properties. 4.2 PRE-FIELD ACTIVITIES Prior to the initiation of field activities, SAIC obtained Encroachment Permit number#03806 to perform work in the City of Tracy ROW, along the south shoulder of Byron Road. Soil boring permit number #0035559 was obtained from SJCEHD for the installation of 36 soil borings. Copies of the permits obtained for this investigation are included in Appendix B. 3