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MW -9 through MW -12 were each completed to approximate depths of 65 feet and screened from approximately 40 to 65 feet bgs Elevated levels of fuel hydrocarbon constituents were detected in the 25, 40, and 45 -foot soil samples collected from well boring MW -10, and in the 50 -foot sample obtained from ' well boring MW -12 Low to non-detected levels of petroleum hydrocarbon constituent concentrations were detected in the remaining soil samples collected from well borings MW -9 through MW -12 Monitor ' well locations are illustrated on Figure 2 and data obtained during this assessment is summanzed in Table 1 Details of this assessment are presented in the Clearwater Site Investigation and Well Installation Report, dated August 28, 2001 4 3 Previous Site Characterizations — Groundwater In June and July 1995, TPE installed five monitor wells (MW -1 through MW -5) In December 1993, HET installed three groundwater monitor wells, designated as MW -6 through MW -8 In December 1994 and January 1995, BC installed one dual air sparge/soil vapor extraction well (AS-I/SVE-1) and two single completion soil vapor extraction wells (SVE-2 and SVE-3) Since 1994, the depth to groundwater has risen beneath the site from 80 to 50 feet bgs, significantly above the screened interval of wells MW -1 through MW -8 Therefore, in an effort to replace monitor wells MW -1 through MW -8, Clearwater Fhista;lecf iuur groundwater iiioitilvt v cntt with slfandWei SL eeaed intervals, dcsignatea u, ivl ,, -9 through MW -12 In December 2002, ATC Associates Inc (ATC) installed five groundwater monitor wells designated MW -13 through MW -17 in an effort to replace more of the occluded wells Monitor well construction details are presented in Table 2, Monitor and Remediation Well Construction Details ATC performed the most recent groundwater gauging and sampling event on January 16, 2003 During this ' gauging event, the depth to groundwater beneath the site ranged from 55 04 feet (MW -13) to 55 92 (MW - 14) feet During the most recent groundwater monitor event a hydraulic gradient of approximately 0 001 ' vertical feet to horizontal foot (ft/ft) trending towards the northwest was calculated Groundwater conditions are illustrated in Figure 3, Groundwater Summary Map - (January 16, 2003) Analytical results for past and current groundwater sampling events are summarized in Table 3, Historical Groundwater Elevations and Sample Analytical Results, and Table 4, Groundwater Sample Analytical Results for Fuel Oxygenates and Additives 4 4 Previous Pilot Testing and Site Remediation Activities In March 1995, BC conducted vapor extraction and air sparge pilot studies at the site Soil vapors were extracted from SVE-2 at flow rates ranging from 20 to 40 standard cubic feet per minute (scftn) at induced vacuums ranging from 64 to 110 inches of water column (inwc) Soil vapors were extracted from SVE-1 at flow rates ranging from 38 to 40 scfm at induced vacuums ranging from 108 to 116 inwc Air was infected into AS -1 at a flow rate of 8 scfm under pressures ranging from 26 to 38 pounds per square inch (psi) Based on the results of the vapor extractioniair sparge pilot studies, it was estimated that each vapor extraction/air sparge well would have an approximate radius of influence of 40 feet Details of this assessment are presented in the BC Corrective Action Plan, dated May 1995 '40 EZ 100966 CAP S 1EZ Serve\EZ I00966\Reports1100966CAP 4 ATC Associates hie ATC Project No 43 25827 0026