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04 February 2000 AGE-NC Project No. 98-0433 ' Page 4 of 5 4.0. SUMMARY AND CONCLUSIONS 1 Based upon the data collected during the January 2000 monitoring event, AGE concludes: ' Ground water at the site was encountered at approximately 18.42 to 20.16 feet bsg. The prevailing ground water flow direction in this area of Jimco is generally toward the west and ' locally somewhat northwest and southwest. • The highest concentration of dissolved hydrocarbons quantified as TPH-g and TPH-d is in the area of monitoring well MW-1 located adjacent to the former UST area. TPH'g and TPH- d in ground water decrease eastward in the area of well MW-7 and decrease south of the former USTs, in the area of well MW-8. • Benzene was detected at the greatest concentration in well MW-1 at 820,ug/l. MTBE was detected in wells MW-I and MW-3 at concentrations ranging as high as 5,400 µg/l by EPA Method 8020; MTBE was detected in wells MW-1 through MW-4 at concentrations ranging as high as 7,400µg11 by EPA Method 8260. • DIPE was detected in well MW-8 at a concentration of 7.8 4g/l, and TBA was detected in MW-2 at a concentration of 21 ,ug/l. ' 5.0. RECOMMENDATIONS Based on the results of this investigation, AGE recommends the following: • Quarterly monitoring at the site should be conducted to coincide with.the monitoring ' performed at-the Ripon Farm Service site. The next monitoring event should be scheduled for April of 2000 and should include sampling of on-site domestic wells for analysis for constituents of concern. ' • A work plan for installation of necessary wells and to assess feasibility of various corrective action alternatives should be prepared. • A Corrective Action Plan (CAP) should be prepared upon completion of the .feasibility testing. The CAP should include remediation feasibility studies (e.g. in-situ air sparging pilot ' test, soil vapor extraction, soil excavation and bio-enhanced remediation or attenuation) to determine appropriate remedial options for the site. The CAP should also include a well receptor survey to determine if local domestic water wells, beyond the domestic well that ' serves the Jimco site, may be at risk from the dissolved petroleum at the site. Advanced GcoEnvironmental,Inc.