ARCHIVED REPORTS_2014_7 - Laserfiche WebLink

Home Browse Search

3-3 0 3.3 Geology and Site Soils 3.3.1 Regional Geology The Forward Landfill is located near the geographic center of the Great Valley geomorphic province in northern San Joaquin Valley. The Great Valley lies between the Sierra Nevada Range on the east and the Coast Range on the west. The Great Valley is an elongated asymmetrical structure trough filled with a thick sequence of flat -lying marine and continental sediments. Ground surface elevations at the site range from approximately 30 to 40 feet amsl, sloping generally to the west. Regional topography is shown on Figure 3. Figure 6 illustrates the surface outcropping of regional geologic units near the site. A brief summary of the type and origin of sediments underlying the region, from oldest to youngest, follows. Marine Sequence: The marine sediments of the Great Valley were deposited during the Cretaceous and Early Tertiary Periods (approximately 35 to 150 million years before present). These marine sediments were probably deposited in a miogeosyncline bound on the east by the developing Sierra Nevada Mountain range and on the west by the subducting Pacific Plate. This sequence of marine clays, silts, and sands includes (from oldest to youngest) undifferentiated upper Cretaceous sandstone and siltstone, undifferentiated Tertiary sandstone and shale, the Capay Shale, the Domengine Shale, the Nortonville Shale, and the Markley Formation. This sequence is approximately 5,250 feet thick under the site. Continental Sediment Sequence: The Great Valley in the area around Stockton was uplifted at the end of the Eocene and was eventually cut off from the Pacific Ocean on the west by subduction and/or accretion events which uplifted or emplaced the present day Coast Ranges. Sediments derived from the eroding Sierra Nevada in the east and the Coast Ranges in the west were deposited in the Great Valley by rivers and streams from about 35 million years ago to the present. In the vicinity of the Forward Landfill, the marine sediments are generally overlain by approximately 2,500 feet of unconsolidated Tertiary and Quaternary sediments of (from oldest to youngest) the Valley springs, Mehtren, Laguna, and Victor Formations. Sediments of these formations were deposited by the activity of the major streams in this area that meandered across the valley floor. The most recent deposit, the Victor Formation, is typically heterogeneous and laterally and vertically discontinuous, indicative of a fluvial depositional environment. The Victor Formation is generally coarse-grained, but is slightly clayey in the interfan sediment areas near Forward Landfill. In this area, the Victor Formation is approximately 100 feet thick. 3.3.2 Site Geology The geology and hydrogeology (discussed further in Section 3.7) of the Forward Landfill have Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\itd-5 yr pr 2013\text\sec 3_final.doc