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® Removal of top 18 to 24 inches of burned material, ash and visibly affected soil within gravel pit area Removal of localized areas of deeper soil containing elevated concentrations of metals or pyrolytic oil. Description of Environmental Setting: The project site consists of an approximately 50-acre former gravel pit situated in the central western part of the Great Valley of California geomorphic province. The valley is bounded by the Diablo Range or Coast Range geomorphic province to the west and Sierra Nevada geomorphic province to the east. The Site lies on the lower edge of coalescing alluvial fans deposited by intermittent streams originating from the Diablo Range. The site location is part of a synclinal trough that is filled with alluvial sediment from both the Coast Range and the Sierra Nevada Mountains (USGS 1971). The natural topography surrounding the gravel pit dips gently to the northeast and is approximately 165 feet above mean sea level. The nearest surface water in the vicinity of the Site consists of Delta Mendota Canal (located yz mile to the southwest)and California Aqueduct (located 1 mile to the southwest). Neither of these two water sources will be affected by remedial activities at the Site. A Banta Carbona Irrigation District Canal borders the gravel pit to the east and Corral Hollow Creek, an intermittent stream, is located 500 feet to the south. A unit of hard silt with varying amounts of clay, sand, and gravel commonly encountered at approximately 90 feet bgs represents the practical limit to which gravel can be mined in the area. The unit is commonly referred to as clay; however, discrete soil samples were collected and logged as silts by geologists in the State of California at two locations within one mile of the Site (E&EI 2000). A gravel road leads into the gravel pit from the northern corner of the Site. The road splits near the entrance and leads along several different routes to different regions of the Site. The topography of the ground surface is varied due to the former mining operations. The approximate elevation of the natural grade around the perimeter of the gravel pit at the project site is approximately 165 feet above mean sea level (msl). The elevation of the average depth within the gravel pit is approximately 110 feet msl. The lowest average elevation of the burn areas is approximately 100 feet msl. Based on recent well surveys and U.S. Geological Survey(USGS) data, the elevation of groundwater at the Site is approximately 65 feet msl, which results in approximately 35 feet of soil between the ground surface and groundwater in the areas intended for excavation (USGS 1995). It is anticipated that excavation of soil will not exceed 10 feet below ground surface. Analysis of Potential Impacts: Describe to what extent project activities would: a. Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault. (Refer to Division of Mines and Geology Special Publication 42) 27