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1 ppb, respectively, which is marginally above the laboratory detection lima of 0.50 ppb Subsequent quarterly groundwater sampling of the monitoring wells has not detected petroleum ' hydrocarbon constituents above method detection limits Analytical results of the initial investigation and subsequent groundwater sampling are summarized in Tables 1 and 2, respectively On December 21, 1993, Wright Environmental Services, Inc (Wright), on behalf of THS, removed and disposed of a 1,000-gallon diesel UST from the subject site. No soil samples were ' collected from the UST excavation, however, obvious contamination was observed in the excavation at the time of the tank removal The open excavation was subsequently lined with ' 10 mil plastic sheeting and backfilled with 314-inch crushed rock and capped with asphalt The San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD)has requested additional work be performed at the subject site 3.0 HYDROGEOLOGIC SETTING The site is located at 315 East Eleventh Street (Business Loop 205), Tracy, California (Figure ' 1) The site is situated on level terrain underlain by flood basin deposits of Pleistocene and Holocene age that are composed of sediments similar to and probably conformable on underlying ' deposits of alluvium and Tulare formation The flood basin deposits consist of light to dark brown and gray clay, silty sand and organic materials with locally high concentrations of salt ' and alkali Stream channel deposits of sand and gravel are also present (Hotchkiss and Balding, 1971) The flood basin deposits of the shallow water beanng zone have well developed soil profiles and consequently poor permeability The quality of the shallow groundwater in the Tracy area is generally poor Regional groundwater within this zone occurs less than 10 feet below grade 1 over most of the Tracy area Regional groundwater gradient is to the north Local groundwater IP 150087/8 053194 FWL 2