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On February 8, 1993, Western Geo-Engineers (WEGE) completed monitoring well MW- <br /> 8 to a depth of approximately 60 feet bgs. The well is approximately 8 feet downgradient <br /> and southeast of the tank field. <br /> On March 14, 1995, WEGE completed a one day vapor extraction treatability test, using <br /> monitoring wells MW-4, MW-8, S-1, and S-2. <br /> USA retained The Park Corporation (Park) to prepare a Remedial Action Plan (RAP). <br /> The rational and design of the necessary environmental remediation and sampling <br /> activities at the site were presented in Park's November, 1995 RAP and in February 28, <br /> 1996 letter to the County. <br /> In October 1997, USA excavated and proceeded to remove the three 12,000 gallon <br /> underground storage tanks (UST's), associated piping, and dispenser islands from the <br /> station. Soil samples were collected from the bottom of the UST complex and submitted <br /> for laboratory analysis. The samples indicated hydrocarbon contamination. <br /> 2.2 Site Geology and Hydrology <br /> The site soils consist of sand layers separated by thin silt and clay units beneath the <br /> northern part of the site that grade into silt and clay beneath the southern part of the site <br /> (Figure 3). Sand units beneath the northern part of the site consist of sands at <br /> approximately 6 to 18 feet bgs, approximately 22 to 30 feet bgs, and approximately 40 to <br /> 60 feet bgs. <br /> Groundwater elevation at the site is approximately 38 feet bgs. The predominant <br /> groundwater flow direction has been to the south and southwest, although occasional <br /> reversal in flow direction has bee observed. Historically groundwater has ranged between <br /> 38 and 53 feet bgs. <br /> 2.3 Local Presence of Water Ways and Off-site Wells <br /> The subject site is flanked by the South Main Canal directly to the east. The South Main <br /> Canal is used seasonally for the transportation of irrigation water from the Mokelumne <br /> River. In addition, there are two off-site wells that are downgradient of the site. One <br /> well is approximately 500 feet east of the site and the other is approximately 2,000 feet <br /> southeast of the site <br /> E.SI:\E:IUSA100651REPORTS\0065P201.DOC-98Vsg:1 Rev.0,1/26/99 <br /> 20A41-007.001 2-2 <br />