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tJ <br /> soil to finish back filling the excavation. The excavation <br /> will be capped with asphalt prior to onset of the rainy <br /> season. <br /> 2.0 SITE DESCRIPTION <br /> 2.1 Topographic and Cultural Features <br /> } , The project site lies on generally flat cultural features <br /> including Highway 120, an orchard, and Building E. <br /> 2.2 Hydrogeologic Setting <br /> I . <br /> The project site lies at the northern end of the San Joaquin <br /> Valley, part of the large northwest trending asymmetric <br /> i- structural trough called the Central Valley. The San <br /> Joaquin Valley contains a thick sequence of sediment which, <br /> °+ in places, reaches a depth of 10 miles. These sediments <br /> range in geologic age from Jurrasic (205million years <br /> before present) ,.o Holocene (present time) and include both <br /> marine and continental rocks and deposits (Page, 1989), <br /> The project site is located on older alluvium, of <br /> Pleistocene and Holocene age. It consists of interbedded <br /> zones of gravel, sand, silt and clay, with some hardpan <br /> ha . <br /> The older alluvium ranges in thickness from about 0 to 400 <br /> feet in the Ripon area,. <br /> y't The water table beneath the site lies at about 45 feet below <br /> grade and flows southwest based on San Joaquin Flood Control <br /> and Conservation District data. The only surface water <br /> ip bodies within one-half mile of the site are irrigation <br /> canals. <br /> 3.0 CONCLUSIONS/RECOMMENDATIONS <br /> Field observations and laboratory results indicate that the <br /> subsurfara was impacted by spills caused by overfilling of <br /> the abssve-ground gasoline tank and possibly the underground <br /> gasoline tank. <br /> -� Excessive soil was excavated to ensure that all the <br /> contamination was removed. Because of the extensive <br /> excavation and laboratory results confirming removal of <br /> petroleum contaminated soils, it is WaterWork's opinion that <br /> the water table beneath the site has. not been significantly <br /> impacted by hydrocarbons. Groundwaterwas; not encountered <br /> in, the excavation which reached `approximately 28 feet below <br /> grade: However, due to groundwater being at less than 50 <br /> feet _below grade--the-San-Joaquin-_Public--Health--Services---- --- -- - -- <br /> -- would normally require a groundwater investigation. ' The <br /> installation of three monitoring wells to determine the <br /> local groundwater gradient is usually required, if ae <br /> 3 <br />