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15 January 2001 AGE-NC Project No 98-0433 Page 4 of 5 ,y • Ground water at the site was encountered at approximately 18 50 to 22 20 feet bsg The prevailing ground water flow direction is generally toward the southwest with very low hydraulic gradients • 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 concentrations 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 • The greatest concentration of benzene was detected in well MW-1 Benzene was also detected in MW-2 The benzene plume is fully defined by MW-4 to the north, MW-3 and MW-5 to the west, MW-8 to the south and MW-7 to the east • MTBE was detected in wells MW-1, MW-2, MW-3 and MW-4 at concentrations ranging as R high as 8,400µg11 The MTBE plume is generally defined by MW-8 to the south, MW-7 to the east, wells MW-3 and MW-5 to the west and to the north by well MW-4 (MTBE detected at 6 5 µg11) • D1PE and TBA were detected in well MW-8 at concentrations of 3 5 µgll and 11 ug/l, respectively = S.U. RECOMMENDATIONS Based on the results of this investigation AGE recommends the following • Quarterly monitoring at the site should continue to coincide with the monitoring performed at the Ripon Farm Service site The next monitoring event should be scheduled for January 2001 and should again include sampling of on-site domestic wells for analysis for constituents of concern • A work plan for installation of necessary wells to assess feasibility of various corrective action alternatives should be prepared The work plan should also detail procedures to assess the vertical limit of dissolved MTBE in the ground water At a minimum two soil borings ' should be advanced, with appropriate technology„to sample discrete ground water zones • A ,Corrective Action Plan (CAP) should be prepared upon completion of the feasibility testing and vertical assessment 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 hydrocarbon plume at the site ` N Adiarreed(.eoEiivir1)IImcilial Inc 1