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3-4 been detailed in several reports including Kleinfelder & Associates (1991) and California Department of Water Resources (2003). These studies confirm that the geologic and hydrogeologic conditions at the Forward Landfill are consistent with regional conditions. As determined in exploratory boring and well installation programs performed at the site, geologic materials beneath the site occur as lenticular units composed of clay, silt, and sand with minor amounts of gravel. Bedding is typically discontinuous over distance and ranges in thickness from a few inches to approximately 20 feet. This variability is consistent with deposition in a fluvial environment where the course of rivers or streams meanders and is subject to frequent flooding. The sediments observed in borings at the site appear to correspond with the Pleistocene age Victor Formation and can be divided into three large groups based on gross lithology and pervasive distinctions in color. Group A. Surface to approximately 28 to 40 feet below ground - Highly interbedded sandy silt, clayey silt, silt, and clay. A few layers of sand. Generally sands are fine grained. Most of the sediments have an oxidized appearance as an orange brown color. Group B. Top: 28 to 40 feet deep, to bottom: approximately 55 to 75 feet deep (25 to 35 feet thick) - Interbedded sand, silty sand, silt, and a little clay. Sands are fine grained. Overall a little sandier than Group A. Sediments are distinctly less oxidized than Group A showing a gray brown color. Group C. Top: 55 to 75 feet deep, bottom: approximately 110 feet deep - Sediments dominated by fine- to medium -grained sand; some coarse-grained or gravelly layers. A few layers of silt and clay material occur. Color is generally light brown to yellow brown. Grains are large enough to assess that the sediments appear to be granitic in origin. A few monitoring wells downgradient of the former Austin Road Landfill, drilled to deeper levels up to 160 feet below ground surface (bgs), encountered a 40 -foot thick unit of clay at approximately 120 and 160 feet bgs. This clay unit could represent an effective aquitard (barrier to flow of groundwater), insulating the upper Victor Formation Saturated Sediments with residual volatile organic compound (VOC) contamination from migrating to the aquifer materials below the 160 -foot depth. However, as there is a limited set of deepwells reaching this formation, the continuity of the potential aquitard unit is not known. 3.4 Faulting and Seismicity The Forward Landfill is located in an area of relatively low seismic activity. It is not located in an area of rapid geologic change. The nearest known fault to the site, the Tracy -Stockton Fault Zone, passes through the City of Stockton, approximately 6.5 miles northwest of the site. This fault zone is the closest known to the landfill and does not show evidence of Holocene displacement. No special setback requirements are therefore needed for the landfill to Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\jtd-5 yr pr 2013\text\sec 3—final.doc