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21 March 2006 <br /> AGE-NC Project No 97-0290 <br /> Page 2 of 15 <br />' the north The western and eastern boundaries of this province are comprised of the California Coast <br /> Range and the Sierra Nevada, respectively The province is subdivided Into two mayor divisions, <br /> designated the Sacramento and San Joaquin Valleys According to the Geologic Map of California, <br /> published in 1977 by the State of California Department of Mines and Geology, the subject site is <br /> underlain by Pleistocene and Holocene alluvium composed of unconsolidated to semi-consolidated <br /> alluvial, playa, lake, and terrace deposits <br /> 23 LOCAL GROUND WATER SETTING <br /> IHistoric depth to ground water at the site has ranged from approximately 3 5 feet below surface grade <br /> (bsg) in 1971 to 55 feet bsg in 1993 and 1996, based upon ground water maps prepared by the San <br /> I Joaquin County Flood Control and Water Conservation District between 1971 and 1996 Ground <br /> water currently occurs at a depth of approximately 43 feet bsg <br /> Current ground water flow direction at the site is toward the south Historical flow directions may <br /> have varied due the influence of the pumping of municipal wells near the site Historic operation of <br /> nearby municipal wells may account for the deeper northerly and easterly extent of contaminants <br /> Nfrom the site <br />' 2 4 UNDERGROUND STORAGE TANK REMOVAL <br /> AGE has been Informed that four underground storage tanks (USTs) and one 55-gallon drum were <br /> removed from the site on 21 September 1987 by Jim Thorpe Oil The USTs ranged in volume from <br /> 250 to 2,000 gallons and were used to store gasoline and waste oil Petroleum hydrocarbons were <br /> detected in soil samples collected beneath the USTs at concentrations as high as 1,300 parts per <br /> million (ppm) <br /> 25 EXCAVATION OF HYDROCARBON-IMPACTED SOIL <br /> I On 25 February 1989,impacted soil was excavated from the former UST area by Warren E Gomes, <br /> Inc of Rio Vista The excavation reportedly encompassed an area of approximately 40 feet by <br /> 40 feet and extended to a depth of approximately 22 feet bsg The excavation was backfilled to grade <br /> with sandy loam <br /> On 13 October 1989, soil was excavated at the southeast corner of the property to confirm the <br /> Iremoval of impacted soil during the February 1989 excavation The second excavation addressed an <br /> area approximately 8 feet by 12 feet and extended to a depth of 26 feet bsg One sample was <br /> Advanced GeoEwnronmentai,Inc <br /> I <br />