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� v <br /> A S S O C I A T E S I N C <br /> Based on groundwater elevations measured on June 8, 2000, the direction of groundwater flow is <br /> generally toward the northeast at an approximate gradient of 0 004 ft/ft The groundwater gradient <br /> measured on June 8, 2000 is shown on Figure 3 The direction of groundwater flow has ranged <br /> ' from east to northeast since groundwater monitoring was initiated in July 1997 <br /> 3.0 SUMMARY OF SOIL AND GROUNDWATER CONDITIONS <br />' 3 1 Extent of Hydrocarbon-Impacted Soil <br /> The lateral extent of total petroleum hydrocarbons as gasoline (TPHg) in soil is delineated by <br /> borings MW5 to the north, boring MW4 to the west, and borings MW6 and SB9 on the east The <br /> highest concentrations of TPHg appear to be in the vicinity of the former USTs, from <br />' approximately 20 feet bgs to 30 feet bgs TPHg was detected in soil samples at concentrations <br /> ranging from nondetect to 8,700 parts per million The lateral extent of TPHg in soil is shown on <br /> Figure 7 <br /> The lateral extent of benzene in soil is delineated by borings MW5 to the north boring MW4 to the <br /> g g <br /> west, and borings SB 10 and SB 11 on 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 35 parts per million The lateral extent <br /> of benzene in soil is shown on Figure 8 <br /> 3.2 Extent of Hydrocarbon-Impacted Groundwater <br />' Based on the analytical results from groundwater samples collected from wells MW1 through <br /> MW7 and CW and grab groundwater samples collected from borings SB 10 and SB 11 in March <br />' 1999, the lateral extents of groundwater impacted with TPHg and benzene are shown on Figures <br /> 9 and 10, respectively The highest concentrations of petroleum hydrocarbons are present in <br /> wells MW1 and MW3 The contamination beneath the site has migrated to the adjacent property <br />' east of the site <br /> 4 0 PILOT TESTING PROCEDURES AND RESULTS <br /> 4.1 Vapor Extraction/Air S ar a Testing— May 17 and 18 2000 <br />' 4 1.1 Methods and Procedures <br /> On May 17 and 18, 2000, ATC performed a long-term vapor extraction test and a short-term air <br /> sparge test followed by a combination vapor extraction/air sparge test The purpose of these tests <br /> l was to evaluate vapor extraction and air sparging as viable remedial options for impacted soil <br /> and groundwater at the site and to determine whether vapor extraction could sufficiently capture <br /> W 1625961reportslpilotcap doc 4 <br />