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' 28 May 1991 <br /> GeoAudi.t CV 43C4 . 1. 1 - Work Plan for Vacuum Extraction <br /> ' Page 3 of 10 <br /> The fresh water bearing formation, consisting of alluvial sediments <br /> ' occurs in a shallower depth. These two aquifers are hydraulically <br /> separated from each other. <br /> ' The ground water is considered as beneficial use and is used for <br /> irrigation, municipal and industrial purposes with moderate <br /> utilization for domestic use (California 's Groundwater, Department <br /> of Water Resources Bulletin no. 128) . <br /> 1 <br /> 1. 3 . SITE SPECIFIC SETTING <br /> ' This following site specific information is obtained from a report <br /> (Problem Assessment Report Continuing Subsurface Hydrocarbon <br /> ' Investigation) prepared by Groundwater Technology, Inc. (GTI) , in <br /> November 1988 : <br /> The prevailing soil profile consists of clean sandy fill from <br /> the surface to a depth of 15 feet, a layer of alternating <br /> sandy clay and clayey sand from 15 to approximately 32 feet, <br /> silty sand from 32 to 42 feet, and loose sand from 42 to 50 <br /> ' feet (bottom of profile) . Saturated conditions were <br /> encountered at 41 feet during the installation of monitoring <br /> wells in 1988 . <br /> ' When surveyed in 1988 , the water table was relatively flat, <br /> showing an average hydraulic gradient of 0. 007 . The prevailing <br /> ground water flow direction was to the north to north-east. <br /> 1. 4 . PREVIOUS INVESTIGATIONS <br /> A single 350 gallon gasoline tank was removed from the site on 21 <br /> September 1989. An unauthorized release of hydrocarbons was <br />' encountered following the removal. Further investigation was <br /> required by the San Joaquin County - Environmental Health Division <br /> (SJEHD) , the lead agency to enforce the State Hazardous Waste and <br /> Underground Storage Tank Laws for the site. <br /> The impact of this release on the vadose and saturated zones was <br /> investigated by Groundwater Technology, Inc. (GTI) . In conjunction <br /> With this investigation GTT drilled seven soil borings and <br /> subsequently converted these borings to ground water monitoring <br /> wells MW-1 through MW-7. The vadose zone contamination is <br /> restricted to the immediate area below the former tank location <br /> (MW-2) . Free product was encountered in two wells (MW-1 and MW-2) . <br /> Water samples from the remaining wells did not indicate the <br /> presence of free product or dissolved hydrocarbon contamination <br />