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I <br /> =AWAW!'A7 <br /> Working to Restore Nature <br /> 1 <br /> The test indicated that a radius of influence of 19 feet and a sparge well spacing of <br /> approximately 38 feet be used to design the sparge well field for this site Due to the <br /> significant expense associated with installing sparge wells to the necessary depths of 70 to <br /> I 75 feet bsg, the installation of a limited number of sparge wells located where the majority <br /> of source gasoline is located, followed by system monitoring is a cost effective approach to <br /> address groundwater restoration If system monitoring during sparging indicates that the <br /> actual radius of influence is inadequate to provide the necessary remedial coverage, the <br /> installation of additional sparge wells should be evaluated <br /> A 19-foot radius of influence requires the installation of two additional air sparge wells (AS- <br /> I 2 and AS-3) to provide sparge coverage of the capillary fringe and groundwater zones that <br /> contain the most hydrocarbon mass These zones are located beneath and adjacent to the <br /> existing USTs The estimated radius of influence for the sparge wells is shown on Plate 6 <br /> I . To monitor sparge system performance, we recommend the installation of one additional <br /> sparge monitoring point (MS-4) <br /> 4.0 SUMMARY OF SOIL AND GROUNDWATER CONDITIONS <br /> 41 Extent of Hydrocarbons in Soil <br /> I The lateral extent of gasoline hydrocarbons in soil is delineated by borings B-8 and B-9 on <br /> the north, borings B-2 and B-22 on the west, boring B-14 on the south, and borings B-6, B- <br /> 12, and B-21 on the east (Plate 2) The highest concentrations of residual gasoline <br /> hydrocarbons are north, south, and west of the tank cavity and south of the dispenser islands <br /> I from approximately 15 feet bsg to the top of the groundwater surface (62 feet bsg) <br /> Residual gasoline hydrocarbons in soil east of the tank cavity and north and northeast of the <br /> dispenser islands are limited to 41 to 61 feet bsg Plates 5 and 6 show the estimated limits <br /> of residual hydrocarbons in the capillary fringe. <br /> 30003-13 6 <br /> I <br />