SITE INFORMATION AND CORRESPONDENCE

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Soil and Groundwater Investigation Report Mountain House Development Site#6 July 2008 2. BACKGROUND 2.1 LOCATION AND SITE DESCRIPTION The site is in an agricultural area northwest of the City of Tracy in San Joaquin County, California (Figure 1). The Mountain House study area is situated at elevations ranging from approximately 20 to 30 feet above mean sea level in relatively flat-laying areas. The site is located along the 0.5-mile stretch of West Byron Road between Wicklund Road and West Bethany Road(Figure 1). 2.2 HISTORICAL AND EXISTING PIPELINES The site includes rights of way(ROWs) associated with a former Standard Oil of California(Standard) Wait-Mendota-Richmond pipeline (the OVP), and the former TAOC pipelines. The OVP traverses the site immediately south and west of Byron Road. The OVP was installed between 1902 and 1904 as a"hot line"(i.e.,the oil was heated to facilitate transmission), and carried San Joaquin Valley crude oil(SJV crude)north from the Kern River Oil Fields (in and near Bakersfield)to Standard's Richmond Refinery. The OVP and associated pump stations operated from 1903 until the early to mid 1930s. The pipeline was again used during the early 1940s to primarily transmit Bunker C fuel oil from the Richmond Refinery to railroad hubs in Tracy. The OVP northwest of Tracy may have also been used to transport crude oil to various markets in the Bay Area until the late 1960s; it was reportedly abandoned in 1970. Where the pipeline was not abandoned in place, it was removed and the trenches likely backfilled with excavated native soil. The former TAOC pipelines ROW traverses the site immediately north and east of West Byron Road in the Union Pacific Railroad(UPRR)ROW. The TAOC dual-pipeline system was constructed in 1907 and transmitted heated crude oil from Bakersfield to the Bay Area. The pipelines were abandoned in the 1970s. Two active pipelines exist in the UPRR ROW: the Kinder Morgan Energy Partners (KM)pipeline and the Chevron Pipeline Company's Bay Area Products Line(BAPL). These lines carry refined petroleum products. 2.3 HYDROGEOLOGIC SETTING The site is in the San Joaquin Valley Groundwater Basin,which is divided into nine sub-basins. The site lies within the Tracy sub-basin(Groundwater Basin Number 5-22.15),which is defined by the areal extent of unconsolidated to semi-consolidated sedimentary deposits that are bounded by the Diablo Range to the west,the Mokelumne and San Joaquin rivers to the north,the San Joaquin River to the east, and the San Joaquin-Stanislaus county line to the south. The Tracy sub-basin is adjacent to the eastern San Joaquin sub-basin to the east and the Delta-Mendota sub-basin to the south(California Department of Water Resources [DWR],2003). The Tracy sub-basin is comprised of continental deposits of late Tertiary to Quaternary age,which includes 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 near the eastern margin of the basin. The Tulare Formation consists 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 at 15 to 250 feet below ground surface(bgs) and the lower aquifer is reported at 600 feet bgs (DWR, 2003). Given the location of the site within the sub-basin,the site is likely immediately underlain by Younger Alluvium, Older Alluvium, and/or Flood Basin Deposits. Data from previous investigations at an adjacent site indicate soils encountered at this vicinity are low- permeability,unconsolidated silts and clays with minor amounts of poorly graded sand and gravel. Groundwater was first observed at depths ranging from 7 to 17 feet bgs during the 2001 site investigation 2 = J= :: merit`& From Science to Solutions