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•, Site"Backgrouind'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 I). One house and a detached garage/storage area are currently located on the,property.,An apartment complex is-located imnrzediately west of the former UST area; r"esidences 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 GEOLOGICMYDROGEOLOGIC SETTING The property is situated within- the Great-Valley Geomorphic.Province of California, a large, I '.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 Iin 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 defiried-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 13,56u--square-mile Sari Joaquin Valley Ground Water Basin(Basin 5-22). This basin is drained primarily by the San Joaquin River. Ground watery. 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 ap proximately 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 soifsarriples submitted'for.geotechnical analysis, the.upper clay layer.appears to have I, a lower ermeabili ' than the saturated;sand and ravel locall encountered below°a rox'imatel p ty ., g Y _ pp Y . . 1.0 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. Advanced GeoEnvironmenfai,Ine. . ,