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monitoring wells, two (2) off-site monitoring wells, and one (1) on-site recovery <br /> (extraction) well. Several wells initially had free-product (up to 3.0 feet in thickness). <br /> �r <br /> Approximately 600 gallons of free-product hydrocarbons were initially removed by the <br /> ;. <br /> extraction system (in addition to an estimated 500 gallons of product recovered during <br /> tank excavation). In 1988, four (4) additional off-site wells were installed. All of the <br /> monitoring wells aria currently on a quarterly monitoring system, and maximum <br /> s quantities of detectable floating product arse currently reported as a film or tree. <br /> f Chevron Station No.94275 <br /> This Chevron station, located 700 feet ENE of the Exxon station, was remodeled in <br /> early 1989• All USTs were excavated and replaced. Petroleum hydrocarbons were <br /> detected in soils excavated from the UST pit. Five (5) monitoring wells were installed <br /> and are currently on a quarterly monitoring schedule. <br /> REGIONAL GEOLOGY/HYDROLOGY AND WATER USAGE <br /> Geologic Setting <br /> - ; - The site is located in the San Joaquin Malley portion of the Central Valley of <br /> California. The Central Valley lies east of the Coast Ranges and extends 650 km in a <br /> NW-SE orientation with an average width of 80 km. This basin is an asymmetric <br /> synclinal trough containing Jurassic to Holocene sedimentary rocks and sediments with a <br /> maximum thickness of 10,000m in the San Joaquin Valley (Repenning, 1960). The <br /> western part of the basin contains the thickest sedimentary section. In addition to this <br /> asymmetry,the basin also has a regional southward tilt. <br /> The Jurassic, Cretaceous and Tertiary sedimentary rocks and deposits consist of <br /> siltstone, claystone, sandstone, and conglomerate (m order of prevalence) thatare of <br /> predominantly marine origin (Heckel. 1966). The source area for these sediments was <br /> most probably the Klamath and Sierra Nevada Mountains (Bailey, et al., 1964). <br /> Pleistocene and Holocene sedimentation of predominantly fluvial and lacustrine <br /> mechanisms has resulted in generally unconsolidated sediments of 30m to 1000m <br /> thicknesses <br /> (Poland and Evensan, 1966). <br /> 2-5 <br /> 175-07.24 ,24/91 <br /> r' <br />