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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 by 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 that extends from the Tehachapi Mountains in the south to the Klammath Mountains in the north. The California Coast Range and the Sierra Nevada form the western and eastern boundaries of this province. Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origin. 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. STRATIGRAPHY Soil consisting of brown- to tan-colored clay, clayey silt, or clayey fine sand were encountered from surface grade to between 13 and 17 feet below surface grade (bsg). Between 13 and 17 feet bsg, the soil is composed predominantly of fine to coarse sand and gravel. Laterally, the coarser-grained soil appears to be localized in a northerly trend along the east side of the property. Two soil samples, one from the uppermost, fine-grained layer and one from the underlying sand and gravel layer, were collected from soil borings B18 and B17, respectively, and analyzed for geotechnical properties. The fine-grained sample, collected from 5 feet bsg at boring B18, was described as a mottled brown clay and clayey sand, with 40% porosity and a low organic content (1.5%). The sand sample, collected from 15 feet bsg in boring Advanced GeoEnvironmental,lite.