ARCHIVED REPORTS_XR0013116 - Laserfiche WebLink

Home Browse Search

2.0 SITE SETTING AND BACKGROUND INFORMATION The following sections provide a discussion of the setting and background information for the Site. 2.1 SITE LOCATION The Site is located at 502 E. Grant Line Road, in Tracy, California (Figure 1). The Site occupies approximately 5.22 acres of property and is bound to the north by the existing PG&E substation which supplies electricity to a majority of the Tracy area; to the south by Hines Field, a vacant lot; to the east by a recently constructed industrial park; and to the west by railroad tracks owned by Southern Pacific (Figure 2). There are also residential properties located southwest of the Site just beyond the Southern Pacific Railroad right-of-way. The Site is currently owned by PG&E and is used as a Service Center. The Site Assessor's Parcel Number is 250-270-08 and is shown on the Assessor's Parcel Map (Figure 3). 2.2 SITE SETTING 2.2.1 Topography and Drainage The Site is located in the northwest central portion of the San Joaquin Valley between the San Joaquin River (east), the Coastal Range (west), and the Old River, a former channel of the San Joaquin River (north), an area with very little topographic relief. The local topography slopes gently to the north-northeast at approximately a 0.4 percent (0.004 feet/foot) gradient (EDR, 2007). The Site drains to the west via concrete swales and asphalt that is graded toward the concrete swales. 2.2.2 Geology and Soil Types The Site is located within the southern portion of the Great Valley Geomorphic Province, which is a topographic and structural basin, bound on the east by the Sierra Nevada fault block and on the west by the Coastal Range. The basin is filled with a thick sequence of alluvial sediments and sedimentary rocks from Jurassic (approximately 200 million years ago) to recent Holocene deposits (PG&E, 1989). The alluvial materials were generated primarily from the Coastal Range with limited contributions from Sierra Nevada Mountains. The alluvial fan deposits are described as comprising a heterogeneous and discontinuous sequence of gravels, sands and clays. The alluvial fan deposits are approximately 100 feet thick in the vicinity of the Site (CDWR, 1967). The alluvial fan deposits are underlain by the Tulare Formation of Pliocene-Pleistocene age (approximately 700,000 to 5,000,000 years ago). This Formation is comprised of semi- consolidated deposits of clays, sands, and gravels that are lenticular and highly discontinuous. However, the Corcoran Clay, which is present in the upper portions of the Tulare Formation in the vicinity of the Site, is a major aquitard within the San Joaquin Basin. This aquitard varies in thickness from 0 to 150 feet thick in the vicinity of the Site and is encountered beginning at approximately 300 feet below ground surface (bgs) (Hotchkiss and Balding, 1971). PARSONS 10 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010