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(bgs). Below this depth, a fine to coarse sand and silty clay are present. Similar soils were <br /> reportedly observed to a depth of 15 feet bgs during the 1990 UST removal at the AASF. With <br /> the exception of the former UST location adjacent to the OMS, Versar's PA/SI investigation <br /> exploratory borings were advanced to a maximum depth of 15 feet, and were predominantly 5 <br /> feet in depth or less. At the OMS former UST location, Versar's borings (B-26 and B-27) were <br /> advanced to a maximum depth of 25 feet bgs. Soils encountered by Versar comprised clayey <br /> silt, with localized areas of sandy silt, and silty clay. <br /> 1.3 HYDROLOGY AND HYDROGEOLOGY <br /> The Site has been graded and modified to promote surface drainage. Catch basins collect <br /> rainwater for flow north through underground pipes into the adjacent airport storm water system. <br /> Eventually, surface drainage is to Little John Creek, a water course oriented east to west <br /> approximately 1.5 miles north of the Site. Little John Creek flows into French Camp Slough and <br /> eventually into the San Joaquin River. <br /> Groundwater has been measured at the AASF at depths ranging from 37 to 44 feet bgs. Based <br /> on water level measurements, the water table beneath the AASF has been determined to be <br /> essentially flat with an average hydraulic gradient of 0.004 foot/foot(ft/ft) to the northeast. The <br /> first groundwater encountered beneath the Site is considered by the State Regional Water Quality <br /> Control Board(SRWQCB)to be an aquifer of beneficial use. <br /> 2 <br /> 3027-03/104700.4766.230/JUL23'03 <br />