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1• <br /> SITE ASSESSMENT WORK PLAN (OVEREXCAVATION) <br /> Conway Property - 381 West Taddei Road <br /> Acampo, California <br /> 1. 0 INTRODUCTION <br /> In accordance with a request from Mr. Ron Conway, Geological Audit <br /> Services, Inc. (GeoAudit) has prepared this work plan to perform <br /> overexcavation procedures at 381 West Taddei Road, Acampo, <br /> California (the site) . The location of the site is illustrated in <br /> Figure 1. A plan of the site is illustrated in Figure 2 . <br /> 2 . 0 BACKGROUND <br /> 2 . 1 Land Use <br /> The site is located in a relatively flat rural area of northwestern <br /> San Joaquin County (Figure 1) . The property is part of a small <br /> rural subdivision. The surrounding area is used primarily for <br /> agricultural purposes (grape vineyards) . The Mokelumne River lies <br /> approximately 1, 200 feet south and a slough lies approximately 500 <br /> feet north of the site. <br /> 2.2 Previous Work <br /> It is our understanding that one 500 gallon leaded gasoline tank <br /> and one 350 gallon unleaded gasoline tank were removed from the <br /> site on 31 October 1989. The tanks were owned and operated by Lodi <br /> Concrete Pipe Service, which was formerly located at the site. A <br /> slight hydrocarbon odor was noted in the soil under the tanks after <br /> the tanks were removed. <br /> Two soil samples were collected for analyses. TPH as gasoline and <br /> BTE&X were detected in both samples. An overexcavation of the tank <br /> pit was performed on 18 July 1990 and five soil samples were <br /> collected from the walls and floor of the excavation. Hydrocarbon <br /> odors were noted in two samples and laboratory analyses indicated <br /> significant levels of petroleum hydrocarbons (TPH as gasoline at <br /> 4 , 000 ppm and 10, 000 ppm) and purgeable aromatics (benzene at 62 <br /> ppm and 41 ppm; toluene at 87 ppm and 430 ppm; ethylbenzene at 35 <br /> ppm and 150 ppm; and xylene at 293 ppm and 850 ppm) in these <br /> samples. <br /> These results indicate that residual soil contamination remains. <br /> Mr. Harlin Knoll of the PHS/EHD has concluded that contaminated <br /> soil may have been in contact with seasonal high groundwater in <br /> 1986, and therefore a groundwater investigation was warranted. <br /> On April 9, 1993 , four soil borings were drilled at the site. <br /> Borings #1 through #3 were advanced to a depth of 38 feet and <br /> 1 <br />