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URS <br /> Mr. Robert McClellon <br /> October 22,2004 <br /> Page 2 <br /> the north,east,and south.The site is undeveloped. This site was formerly permitted to World <br /> Enterprises from 1970 to 1978 as a debris disposal site(debris from demolished buildings to include <br /> wood,rubble,concrete,and other fill materials). The SJCEHD's site file contained several photographs <br /> of the site taken in 1978. The notes on some of these photographs indicate household garbage was <br /> intermixed with concrete,demolition debris, and construction debris. Records indicating the landfill's <br /> areal extent or its depth were not found. <br /> Geologic and Hydrogeologic Overview <br /> The following information provides a description of the site's geologic and hydrogeologic features. <br /> Regional Geology <br /> Regional lithology consists of alluvial fan deposits and interfan beds of the Victor Formation, which lie <br /> on the irregular upper surface of the Laguna Formation. Subsurface characteristics of the Victor <br /> Formation are unconsolidated discontinuous layers and lenses of gravel, sand, silt,and clay, which <br /> were laid down as alluvial deposits originating from erosion of the Sierra Nevada Range to the east. <br /> Local stream channel erosion and re-deposition of the Victor Formation is attributed to the formation <br /> of the shallow surface sand and gravel lenses. <br /> Site Geology <br /> Site-specific subsurface sediments generally consist of silty sand,clayey sand, sandy silt and sandy <br /> clay from near surface to the maximum depth explored of 20.5 feet below ground surface(bgs). The <br /> depth interval from approximately 0 to 9 feet bgs is dominated by silty sand. A fair amount of wood <br /> debris from the landfill was found to be present in this interval.The depth interval between 9 to 14 feet <br /> bgs is dominated by sandy silt. The depth interval between approximately 14 to 20.5 feet bgs is <br /> dominated by clay with a varying amount of sand. Groundwater was not encountered in any of the <br /> borings. <br /> Hydrogeology <br /> The depth to groundwater at the site was estimated to be approximately 25 to 30 feet bgs (based on <br /> information from other nearby sites,provided by SJCEHD). <br /> Hydrology <br /> The mean annual precipitation for City of Stockton is 10.58 inches. The French Camp Slough is <br /> located less than 1,000 feet west of the site. The Walker Slough is located less than 1,500 feet northeast <br /> of the site. The area surrounding the site is relatively flat. Some areas of the site are uneven,but the <br /> overall site appears to drain to the west. <br /> Summary of Previous Investigations <br /> The California Integrated Waste Management Board(CIWMB), SJCEHD,and URS Group,Inc. (URS) <br /> have conducted several landfill gas investigations at the site. Previous investigations included the <br /> following: <br /> K:\Wprocess\25532\WorldEnterprise\Remediation Plan\Letter.doc <br />