ARCHIVED REPORTS HUMAN HEALTH SCREENING EVALUATION

Home Browse Search

' Human Health Screening Evaluation Surland Homes—Bridle Creek February 12,2009 continue to depict the ROW as SPRR. The Laurelbrook subdivision consists of more than 100 single-family homes over approximately 15 acres, and is one of several tracts of land north of the former OVP ROW that have been recently developed into residential homes. The former OVP transported heavy petroleum (crude and fuel oil) from Bakersfield to the Richmond Refinery from the early 1900s to the 1960s. The former Tidewater Associated Oil Company (TAOC) dual-pipeline system was also located along the southern boundary of the UPRR ROW. The former TAOC pipelines transmitted heavy crude from the Central Valley to the Bay Area from the early 1900s to the 1970s, when it was decommissioned. Where the pipelines were not abandoned in place, they were removed and the trenches were likely backfilled with native soil. The former OVP was reportedly removed along most the alignment, while the former TAOC pipelines were generally left in place. Specific ' information regarding locations where the pipelines remain in place or have been removed is not available. The area north of the UPRR ROW is currently a residential development(Figure 2). A property between a portion of the site and the residential development to the north is reportedly owned by the Tracy West Side Irrigation District. This property has been referred to as a ditch in the past; however, field observations revealed that it is actually a grassy area. The UPRR ROW is currently undeveloped. A small ditch runs along the south side of the wall separating the UPRR ROW and the residential development to the north,but does not appear to be related to the Tracy ' West Side Irrigation District property. Byron Road is located to the south of the UPRR ROW, and there is a residential neighborhood along the south side of Byron Road. The closest surface water is the Lower Main Canal, located roughly 1/z mile south of the site. 1.2 REGIONAL HYDROGEOLOGY Regionally, the site is located within the San Joaquin Valley Groundwater Basin. This basin 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 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 located adjacent to the eastern San Joaquin Sub-basin to the 1 east, and the Delta-Mendota Sub-basin to the south. 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 1 250 feet below ground surface (bgs), and the lower aquifer is reported at 600 feet bgs. Given the location of the site within the Sub-basin, the site is likely immediately underlain by Younger Alluvium, and Older Alluvium and/or Flood Basin Deposits. From Science to Solutions