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Site Background Information WELDON CHURCH PROPERTY ' 104 West Beverly Place, Tracy, California The site is located in a residential area of central Tracy,California,in San Joaquin County(Figure 1). One house and a detached garage/storage area are currently located on the property. An apartment complex is located immediately west of the former UST area; residences are located to the south and east of the site. One small.capacity(550-gallon)UST was installed at the site in the early 1980s. The tank was used to fuel vehicles associated with Church Refrigeration,a company owned and operated Iby Mr. Weldon Church. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The property is situated within the Great Valley Geomorphic Province of California, a large, elongate, northwest trending, asymmetric structural trough. The Great Valley Province has been filled with thick sequences of sediment ranging in age from Jurassic to Recent,creating a nearly flat- lying alluvial plain,extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The western and eastern boundaries of this province are the California Coast Range and the Sierra Nevada, respectively. Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origins. The northern and southern portions of the Great Valley Province have been designated the Sacramento and San Joaquin Valleys, respectively. ' The Modesto, Riverbank and Turlock Lake Formations and overlying recent alluvium are the principal source of domestic ground water in the 13,500-square-mile San Joaquin Valley Ground Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. Ground water Iis considered to be of beneficial use and is used for domestic, industrial and commercial purposes. ISTRATIGRAPHY Tan, silty clay soils were encountered from the surface to depths of approximately six feet bsg, in each boring. Gray, silty clay was encountered between six and ten feet bsg during the installation of the ground water monitoring wells and borings. Coarse sand was locally encountered below the clay, between 10 and 23 feet bsg in the borings established to that depth. Gravel occurred below the sand from 23 feet bsg to 25 feet bsg, in boring MW-6. Based upon soil samples submitted for geotechnical analysis, the upper clay layer appears to have a lower permeability than the saturated, sand and gravel locally encountered below approximately 10 feet bsg. Ground water is present in the sand, however it appears that the clay immediately overlaying the sand may retard the vertical migration of ground water and hydrocarbons. IAdvanced GeoEnvironmental,Inc.