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Section t Introduction and Background • California Department of Water Resources. June 1991. California Well Standards. Bulletin 74-90. 1.3 SITE SOILS, GEOLOGY, AND HYDROGEOLOGY 1.3.1 GEOLOGY The California Department of Mines and Geology(CDMG) Geologic Map of the San Francisco —San Jose Quadrangle indicates that the project area is underline by the Quaternary Dos Palos Alluvial (Basin Deposits) characterized as floodbasin deposits. The CDMG Map Showing Recency of Faulting indicates that the Holocene (active) Vernalis fault is located approximately 1.5 miles to the southwest of the Main Stone Property. Active faults are defined as those which have showed displacement over the past 10,000 years. No other active faults were identified within 10 miles of the project area. Other faults(Pleistocene and later) within 10 miles of the project area include the Stockton Fault approximately 7 miles to the north and northwest, the San Joaquin Fault approximately 8.5 miles to the southwest, and the Black Butte Fault located approximately 10 miles to the southwest. 1.3.2 SHALLOW SOILS COVERAGE Georeferenced shallow soils coverage data were obtained from the National Resources Conservation Service(Soil Survey). According to this source, soils underlying the Main Stone Property are composed primarily of the Columbia(680 acres) and Merritt(352 acres) Series (Figure 2). The Columbia is described as a fine sandy loam, subdivided based largely on drainage and flooding potential. The Columbia is further characterized as being partially drained to drained, locally channelized, occurring on 0 to 2 percent slopes, and in some areas, frequently flooded. The Soil Survey estimates the saturated hydraulic conductivity of the Columbia as between 1.4 x 10-3 to 4.2 x 10-3 cm/sec. The Merritt is described as a silty clay loam that is partially drained on 0 to 2 percent slopes with an estimated saturated hydraulic conductivity of between 1.4 x 10-4 to 1.4 x 10-3 cm/sec. The Columbia and Merit soils are scattered throughout the entire project area(Figure 2). The Willows clay(132 acres)and to a lesser extent the Pescadero clay(17 acres)underlie the southern to southwestern most portion of the property(Figure 2) and are described as being partially drained. The estimated saturated hydraulic conductivity of the Willows clay is between 1.0 x 10-6 to 4.2 x 10-5 cm/sec. The estimated saturated hydraulic conductivity of the Pescadero clay is between 1.0 x 10-6 to 4.0 x 10-4 cm/sec. Another soil present within the project area (generally found in the central to south central portion of the property)is the Grangeville(66 acres), described as a partially drained clay loam(0 to 2 percent slopes)with a estimated saturated hydraulic conductivity of between 1.4 x 10-4 to 4.2 x 10-3 cm/sec. According to the Soil Survey,the remainder of the property is designated largely as water. The soil descriptions and physical properties are provided in Appendix A of this report. May 2006 Main Stone Property 1-2 Effluent Storage and Disposal Site Hydrogeologic Investigation Workplan