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d � v <br /> v <br /> A S S O C I A r E S I N C . <br /> 4.0 SUMMARY OF SOIL AND GROUNDWATER CONDITIONS <br /> i <br /> 4. 1 Extent of Hydrocarbon-Impacted Soil <br /> The lateral extent of TPHg in soil is delineated by boring MW5 to the north, boring MW4 to the <br /> west, and borings MW6 and SB9 to the east. The highest concentrations of TPHg appear to be in <br /> the vicinity of the former USTs, from approximately 20 feet bgs to 30 feet bgs. TPHg was detected <br /> in soil samples at concentrations ranging from nondetect to 8,700 parts per million. The lateral <br /> extent of TPHg in soil is shown on Figure 7. <br /> The lateral extent of benzene in soil is delineated by boring MW5 to the north, boring MW4 to the <br /> west, and borings SB 10 and SB 11 to the east. The highest concentrations of benzene appear to be <br /> j 7 in the vicinity of the former USTs, from approximately 20 feet bgs to 30 feet bgs. Benzene was <br /> Jdetected in soil samples at concentrations ranging from nondetect to 35 parts per million. The <br /> lateral extent of benzene in soil is shown on Figure 8 . <br /> 4.2 Estimated Extent of Hydrocarbon-Impacted Groundwater <br /> The lateral extent of impacted groundwater has not been defined yet. Based on the analytical <br /> ] results from groundwater samples collected from wells MW1 through MW7 and CW and grab <br /> groundwater samples collected from borings SB10 and SB11 in March 1999, the estimated <br /> l lateral extents of groundwater impacted with TPHg and benzene are shown on Figures 9 and 10, <br /> J respectively. The highest concentrations of petroleum hydrocarbons are present in wells MWl <br /> and MW3 . The contamination beneath the site has migrated to the adjacent property east of the <br /> j site . <br /> 5.0 DESIGN PLANS AND SPECIFICATIONS <br /> � I <br /> The proposed soil and groundwater remediation systems will consist of combined vapor extraction <br /> —� and air sparge treatment systems. The systems will function as interim remedial measures for on- <br /> site hydrocarbon impacted soil and groundwater. <br /> j 5. 1 Design Parameters <br /> �j 5.1.1 Vapor Extraction - Wellhead Vacuum, Flow Rate, and Radius of Influence <br /> Uextraction pilot testing performed at the site indicated that a radius of influence (ROI) of up <br /> to 30 fe#t was achieved with air floWratb3^ mg f( `om 8 .3 to 12.2 cubic feet per minute (cfm) and <br /> wel ie <br /> ad vacuums ranging fr 6 21 .0 to 23 .4 inches' of-mercury. The actual radius of influence for <br /> each vapor extraction well Xvary depending on subsurface geologic conditions, the extent and <br /> distribution of hydrocarbon-impacted soil, the effect of concurrently operating the AS system, and <br /> w:\wordpro\62596\reports\irp.doc 4 <br /> �J <br />