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Note This calculation presents a maximum residual diesel fuel volume The area used for <br /> calculation of the residual diesel is bounded by analytical results below detection limits The <br /> average residual insitu diesel fuel concentration should be significantly less than the <br /> maximum diesel fuel content used in this calculation Due to this fact the residual diesel fuel <br /> is likely to be significantly less than the maximum volume calculated This calculation <br /> should be considered an order of magnitude estimate only <br /> 8.0 Extent of Petroleum Hydrocarbons in Groundwater <br /> No groundwater has been encountered during any excavation, soil boring, or vapor extraction <br /> effort at the site to the maximum explored depth of 45 feet below grade <br /> Analysis of a groundwater sample collected in October, 1993 from areexistin n <br /> p g onsite water <br /> well (located approximately 50 feet southwest of the former tank location) revealed no <br /> detectable petroleum hydrocarbon concentrations This well reported intersects an aquifer 135 <br /> feet below grade Table 2 contains groundwater analytical data <br /> 9.0 Remediation Activities and Effectiveness <br /> 9.1 Soil Remediation <br /> Soil Remediation activities performed at the site have occurred in three separate mobilizations <br /> which include <br /> 1) tank and soil excavation and disposal 4188 <br /> 2) soil vapor extraction 5191 - 8/91 <br /> 3) overexcavation and disposal 11/94 <br /> In April 1988 <br /> p , a 1,000 gallon underground storage tank, formerly containing diesel fuel, and <br /> the surrounding fill material (approximately 18 yd or 25 tons) were excavated and disposed <br /> With the removal of this tank, the primary source for any continued petroleum impact to soil <br /> was removed <br /> In January 1991, a soil vapor extraction system consisting of four interconnected vadose zone <br /> wells and an attached blower, were installed at the site in an effort to address residual diesel <br /> fuel concentrations in soil The system was operated a total of 66 days and during that time <br /> removed an estimated 0 5 gallons of diesel Subsequent soil testing data indicated the lack of <br /> MZ/O!-27-95/UST/95-0011 nbr 11 <br />