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TETRA TECH, INC 2.0 SITE CHARACTERISTICS This Section describes the physical, geological, hydrogeological, and ecological characteristics, and discusses the current uses of the surrounding area. 2.1 TOPOGRAPHY,GEOLOGY,AND HYDROLOGY The Site is located on flat terrain along Byron Road in Tracy,approximately 25 feet above mean sea level (msl). The Site slopes slightly to the northeast. The following summary of soil types at the Site was obtained from the United States Department of Agriculture, Natural Resource Conservation Service Soil Data Mart(2007). The dominant soil component at the Site is listed as Capay clay and the surface texture of the soil is described as silty clay. Clay comprises 40 to 60 percent of the soil. The available water capacity is between 0.14 and 0.16 inch of water per inch of soil. Surface water runoff is high. The risk of corrosion is high for uncoated steel and low for concrete. The pH of the soil ranges between 6.6 and 8.4. The Site is located in the southernmost portion of the Great Valley geomorphic province. The Great Valley is a large,northwest trending,asymmetric structural trough that has been filled with as much as six vertical miles of sediment in the San Joaquin Valley (Page 1986). The Great Valley is bounded by the Sierra Nevada Range on the east and the Coast Ranges on the west. The main geological hazards or faults that are likely to affect the Site are surface rupture,ground shaking, liquefaction, lateral spreading, and settlement. Two regional faults of large reverse displacement include the Stockton Arch Fault and the Vernalis Fault.The entire area has been uplifted and tilted to the south by movement on the Stockton Arch Fault (Hoffman 1965). The most prominent regional folds are the Tracy-Vernalis trend and the Lathrop structure. The parallel northwest-trending Black Butte Fault and Black Butte Anticline are located approximately 2.5 miles southwest of the Site. The Black Butte Fault is apparently a reverse fault with small displacement, up thrown on the west side, located on the east side of the Black Butte Anticline(Hoffinan 1965). Hydrogeological data were obtained from the California Department of Water Resources (2004) Groundwater Bulletin 118, a statewide inventory of groundwater basins that includes individual hydrogeologic descriptions for each delineated groundwater basin and related subbasins in California. The Site is located in the San Joaquin Vally Groundwater Basin, specifically in the Tracy Subbasin. It is defined by the unconsolidated to semi-consolidated sedimentary deposits that are bounded by the Diablo Range on the west; the Mokelumne and San Joaquin Rivers on the north; the San Joaquin River to the east; and the San Joaquin-Stanislaus County line on the south. Water-bearing formations in the Tracy Subbasin are comprised of continental deposits of Late Tertiary to Quaternary age. These deposits include younger and older alluvium, flood basin deposits, and the Tulare Formation. The cumulative thickness of these deposits increases from a few hundred feet near the Coast Range foothills on the west to approximately 3,000 feet along the eastern margin of the basin. 2.2 ECOLOGICAL CHARACTERISTICS The Site is located within the Great Valley ecological region, specifically Westside Alluvial Fans and Terraces subsection(USDA 1998). Before land conversion and development,the Site probably consisted of riparian scrub and valley grassland, with Great Valley riparian forest along perennial stream corridors. Like surrounding parcels,the Site was then probably converted to row crop agriculture and orchards. Sampling Effort Work Plan page 2_1 Tracy Mansfield Property