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12 July 2001 <br /> AGE-NC Project No 98-0433 <br /> Page 4 of 5 <br />' 4.0. SUMMARY AND CONCLUSIONS <br /> Based upon the data collected during the April 2001 monitoring event, AGE concludes <br /> • Ground water at the site was encountered at approximately 18 65 to 20 36 feet bsg The <br /> prevailing ground water flow direction is generally toward the southwest with very low <br />' hydraulic gradients <br /> • The highest concentration of dissolved hydrocarbons quantified as TPH-g and TPH-d is in <br />' the area of monitoring well MW-1 located adjacent to the former UST area TPH-g and <br /> TPH-d concentrations in ground water decrease eastward in the area of well MW-7 and <br /> decrease south of the former USTs, in the area of well MW-8 <br />' 0 The greatest concentration of benzene was detected in well MW-1 Benzene was also <br /> detected in MW-2 The benzene plume is currently constrained by well MW-4 to the north, <br />' wells MW-3 and MW-5 to the west, well MW-8 to the south and well MW-7 to the east <br /> • MTBE was detected in wells MW-1,MW-2,MW-4 and MW-8 at concentrations ranging as <br /> high as 3,300 µg/1 The MTBE plume is generally defined by MW-8 (below California <br /> maximum contaminant levels)to the south,MW-7 to the east, wells MW-3 and MW-5 to the <br /> west and to the north by well MW-4 <br />' TBA was detected in wells MW-2 and MW-8 <br />' 5.0. RECOMMENDATIONS <br />' Based on the results of this investigation, AGE recommends the following <br /> • Quarterly monitoring at the site should continue at the site The next monitoring event <br />' should be scheduled for July 2001 and should again include sampling of on-site domestic <br /> wells for analysis for constituents of concern <br /> • A Corrective Action Plan(CAP) should be prepared upon completion of vertical assessment <br />' and analysis of feasibility testing The CAP should include remediation feasibility studies <br /> (e g in-situ air sparging pilot test, soil vapor extraction, soil excavation and bio-enhanced <br /> remediation or attenuation) to determine appropriate remedial options for the site The CAP <br />' should also include a well receptor survey to determine if local domestic water wells (beyond <br /> the domestic well that serves the Jimco site) may be at risk from the dissolved <br />' petroleum-hydrocarbon plume at the site <br /> Advanced GeoEnvironcnenW,Inc <br /> I <br />