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the borings ranged from approximately 90 to 137 feet NGVD. A silty clay layer at the surface extended to depths of two to 12 feet bgs. The remainder of the subsurface profile is dominated by dense, red brown clayey and silty gravels. Relatively thin lenses of silty clay and silty or clayey sands were encountered in each of the borings. The thickest layers I! k (6 to 12.5 feet thick) of silty clay were encountered in borings A-2, B-1, and B-3. Boring B-4 encountered numerous thin layers of sand, silt; and clay '(refer directly to the Kleinfelder report for additional information on the sampling results). it Groundwater was not encountered in any of the borings, including the borings located near the project site boundaries closest to the Delta Mendota Canal (Cl through C4) and California Aqueduct (A-1) which indicates that perched groundwater conditions were not present (Such conditions could be an indication of significant seepage from these water conveyance structures.) Local Soils Soil, as described in this section, is the natural formation of mineral and organic material !, Soils can develop on unconsolidated sediments and weathered bedrock. The development of a soil is typically dependent on five major influences: climate,. topography, biologic activity, parent material, and time. Differences .in soil types are, therefore, caused by changes in these influences.-At the project site and within the site vicinity, different soils have been identified by the U.S. Soil Conservation Service.(USDA,:1992) on the basis of .I characteristics that reflect relatively subtle but important changes in the soil formation ! factors. In general, the topography is relatively 7flat, the climate is similar, and biological activity is comparable. Two soil mapping units have been identified at the project site (USDA, 1992). The majority FI ,. of the site is mapped as Zacharias gravelly clay loam. The northern portion of the project ' - site contains Zacharias clay loam. The major difference in the two soil types is that the !I . surface soil (uppermost horizons) for the clay loam is thicker and more fine-grained. it The Zacharias soils are deep, well-drained soil that is developed on nearly level surfaces underlain by alluvial sediment deposits. Runoff is moderately slow on these surfaces and the erosion hazard is slight. The permeability is moderately slow and the available water �I capacity is high. The shrink-swell potential is moderate. The organic content is relatively low, one to two percent. The Zacharias soils are well-suited for agriculture, particularly when irrigated. Agriculture on these soils throughout the region includes irrigated row, field, and orchard crops and I' some dryland grain crop production. When irrigated,-the gravelly clay loam has moderate limitations to its use for agriculture due to its gravelly texture (Capability Class FIs-4). The clay loam has few limitations for agricultural use (Capability Class 1)when irrigated. Both of these soil mapping units, where irrigated, are considered "Prime f=armland" by the U.S. Soil Conservation Service and the California Department of Conservation. (For additional �! discussion of farmland impacts, refer to Section 4.3.) i E Draft Environmental Impact Report 4-11 ER-96-3 l