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Working to Restore Nature <br /> fringe and saturated zone. The test indicated that a radius of influence of 19-feet can be <br /> achieved, a 19-feet radius of influence requires the installation of two additional air sparge <br /> wells to provide sparge coverage of the capillary fringe and groundwater zones that contain <br /> the majority of the hydrocarbon mass <br /> 7.0 CONCLUSIONS <br /> Based on results of the investigations, RESNA concludes that <br /> o Sediments beneath the site consist primarily of silt with lenses of sand and clay from <br /> the surface to 60 feet bsg and sand with lenses of silt from 60 to 78 feet bsg <br /> i <br /> o Groundwater was encountered at approximately 61 to 68 5 feet bsg during drilling <br /> in sediment consisting of sand under semi-confined conditions The water level in <br /> the water-table aquifer has ranged from approximately 60 to 66 feet bsg. The <br /> direction of groundwater flow has fluctuated from northeast to southeast <br /> o Residualgasoline hydrocarbons are present in soil beneath the site The vertical and <br /> lateral distribution of residual gasoline hydrocarbons in soil has been delineated <br /> The lateral extent of gasoline hydrocarbons in soil is delineated by borings B-8 and <br /> B-9 on the north, borings B-2 and B-22 on the west, boring B-14 on the south, and <br /> borings B-6, B-12, and B-21 on the east The highest concentrations of residual <br /> gasoline hydrocarbons appear to be north, south, and west of the tank cavity and <br /> south of the dispenser islands from approximately 15 feet bsg to the top of the <br /> groundwater surface (62 feet bsg) Residual gasoline hydrocarbons in soil east of the <br /> tank cavity and north and northeast of the dispenser islands appear to be limited to <br /> 41 to 61 feet bsg <br /> I <br /> o Dissolved gasoline hydrocarbons quantified as gasoline are present in onsite and <br /> offsite wells Benzene has been detected in wells onsite, but concentrations were <br /> below laboratory detection limits in offsite wells. Based on the relatively low <br /> concentrations of dissolved gasoline hydrocarbons detected in offsite monitoring <br /> wells, it is our opiruon that no additional assessment is warranted <br /> o Remediation of soil beneath the site is feasible using vapor extraction technology <br /> 3000 -� 11 <br />