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A S S O C I A T E S I N C 3.0 SUBSURFACE CONDITIONS' ' 331 Geology ' The site is situated at an approximate elevation of 5 ft. above mean sea level, in the Great Valley geomorphic province. The Great Valley province is a north-south elongated structural trough filled with sediment from marine and continental sources. The continentally derived sedimentary deposits comprise the upper portion of the valley fill, and were deposited in fluvial, alluvial, and lacustrine environments. ' The soils at the property have been mapped by the United States Department of Agriculture (USDA), Soil Conservation Service as the Jacktone Urban Land Complex. This nearly level map unit is in the basin. The annual precipitation is about 14 inches (USDA, 1992). ' The Jacktone soil is moderately deep to hardpan and is generally poorly drained soil. This soil consists of clay, silt and some sand deposited during flood stages of major streams in the delta area ' including mud, muck, loam and sand. Permeability is slow in the Jacktone soil. Available water capacity is moderate. The rate.of water intake in irrigated areas-is 0.1 inch per hour. Where the Jacktone complex is used for development, the main limitations are high shrink-swell potential, the slow permeability, depth to hardpan, and low strength (USDA, 1992). ' Soil in boring S137 consisted of fill to 7 ft. bgs. Alternating layers of silt, clay, and/or sand were encountered to depths between 50 ft. bgs to 55 ft. bgs. Soil between 55 ft. bgs and 66.5 ft. bgs, the maximum depth explored, consisted of clay with varying amounts of sand. 3.2 Hydrogeology Water level measurements were collected from soil boring SB7 on April 11, 2000. Groundwater was initially detected at 45 ft. bgs and subsequently stabilized at 36 ft. bgs. The site's underlying groundwater gradient could not be determined with a single measurement point, however regional groundwater flow is estimated to be eastward based on San Joaquin County Flood Control and Water Conservation District data (Lines of Equal Elevation of Groundwater, Fall 1997). ' 4.0 ANALYTICAL RESULTS 4.1 Soil Analytical Results The soil sample collected from boring SB7 at 10.5 ft., 15.0 ft., 35.5 ft. bgs contained detectable concentrations of gasoline range hydrocarbons. Additionally, MTBE was detected in the soil ' sample collected at a depth of 50.5 ft. bgs at a concentration of 42 parts per million (ppm). wA92054.000I VeportslsumsbT doc 4