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Site Background Information WELDON CHURCH PROPERTY 104 West Beverly.Place, Tracy, California The site is locatedina residential area of central Tracy,California,in San Joaquin County(Figure Il). + ` One house and,.a-detached garage/storage area are currently.located on the`praperty..An apartment complex is'located irnmediately 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 GEOLOGIG/HYnRO.GEOLOGIC.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 nears flat- lying 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 th'e 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, is considered to be ofben`eficial iise anci.is used far doine5tic, iridixstrial and comrnercial,purposes., • I . STRATI . , GRAPHY .. _ . . Tan, silty clay soils were encountered from the surface to depths of,approximately six feet bsg;irC each boring. Gray, silty,clay was encountered between six and ten feet'bsg during the installation of the groundwater 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. firorri 23 feet.bsg to 25 feet bsg;iri boring,MW-6. , Based upon soil samples submitted for ge'otechnical.analysis;the upper clay" layer appears to have ' a;lower 'permeability.than the saturated 'sand and avel-locall encountered below'a roxirriateI Y, . pp. Y 10 feet bsg. Ground water is present.in the sand,`however"it appears that the clay immediately, Ioverlaying the sand may retard the vertical migration of ground water and hydrocarbons Advanced GeoEnvironmental,Inc.- •