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In July 1999, we drilled an additional monitoring well (MW-12) and a vapor boring to 80 feet, which <br /> was completed for a vapor extraction well , (VW-7). They were reported in our report dated August <br /> 5 , 1999. <br /> In December 2000, we drilled one additional monitoring well (MW-13) which was placed near <br /> (MW-8) so that the slotted casing would be located at a shallower level than (MW-8). <br /> In August 24, 2005, we drilled two monitoring wells (MW-14 and MW- 16) which were placed near <br /> the east side of the station and across Charger Way and Grant Street. In this report we also <br /> described the finding of the boring (B-4) at the southeast side of the station . <br /> C . GEOLOGY <br /> The site and all nearby terrain are underlain by non-marine sediment which are tentatively <br /> assigned to the Modesto Formation of Pleistocene age. The materials penetrated at this site are <br /> clay, silty clay and clayey silt. Sandy strata are present between 25 and 30 feet and below 50 feet <br /> interbedded with silts and silty clay. Bedding is absent or non-distinct but appears to be <br /> essentially horizontal . <br /> D. Surface Water <br /> The closest surface water is the Stockton River channel about 1 mile northwest of the site . The <br /> San Joaquin River Walker Slough is about 2 miles south of this site. <br /> E . Local Land Use <br /> The property is a commercial gas station . The site west of this site is a restaurant and to the east <br /> is a hardware store. South of Charter Way is a series of small commercial buildings and north of <br /> this site is a residential area. <br /> Groundwater Concepts <br /> The Hydraulic Conductivity of the groundwater was tested on April 30, 1993 in wells MW-4, MW-5 <br /> and MW-6. The conductivity was found to be 2 . 94 feet/day. The depth of the water table is 33 <br /> feet and the soil unit was silty sand . This sand extends from the western well MW-9 to just beyond <br /> well MW-8. The average gradient for this site is to the northeast at 0. 00345 and the velocity is <br /> calculated to be 0. 07203 feet per day. During any quarter the water will travel about 6. 3 feet. <br /> III Nature and Extent of Contamination <br /> The vadose soil under the station contains gasoline and oxygenates and still remains. The soil <br /> zone extends to about 30 feet below the surface. There are pockets of contamination in the <br /> vadose zone around all the wells on site. <br /> 4 <br />