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k 10 April 2000 AGE-NC Project No. 95-0137 Page 3 of 4 A minimal flow rate of 200 scfm is proposed for the soil remediation portion of the corrective action plan. This flow rate will allow for mass reduction in the vadose zone, mass recovery from air- sparging of the ground water and minimize the tendency for channelization in the soil. Due to the nonhomogeneous stratigraphy of the RFS site, an unequal remediation response is anticipated from the soil, in other words, fine grained soil will require a greater quantity of mitigation energy, and therefore, a longer time period to meet the corrective action goal for impacted ground water mitigation. 3.0. SOIL VAPOR EXTRACTION WELL CONSTRUCTION As discussed above, the nonhomogeneous stratigraphy will probably cause an unequal remedial response to mitigation effort on the impacted soil. For ground water mitigation, soil vapor recovery wells will need to be installed at the water table. To best assess shallow vapor extraction well depths and screen placement, additional soil cores will be required. To best characterize the vertical and horizontal distribution of fine grained and coarse grained soil underlaying the site, four soil borings will be continuously cored, in conjunction with the installation of in-situ air-sparging wells. After the soil types are determined two well sets will installed according to the procedure outlined in the RWAP. One set of vapor recovery wells will be installed with screens from 15 feet bsg to 20 feet bsg to collect actively sparged soil gas/vapor from the water table. Other wells will be installed above 15 feet bsg, with screen intervals, of less than five feet, in selected soil horizons based on the soil composition and observed hydrocarbon concentrations. 4.0. PROGRESS MONITORING Monitoring the progress of the remediation effort will consist of the ground water monitoring, field monitoring of the extracted soil vapor and laboratory analysis of extracted soil vapor and treated soil vapor. Quarterly ground water monitoring and sampling will be performed at the site on monitoring wells MW-I through MW-8 throughout the remediation period to monitor remedial progress. All approved ground water monitoring points will be monitored as described in quarterly reports predating this addendum, and in accordance with established guidelines. Influent vapor concentrations, effluent vapor concentrations at the thermal oxidizer unit and the operational parameters (combustion temperature, volume of processed vapor, oxygen level and the lower explosive limits (%LEL) or organic vapor level will be monitored on a weekly basis to ensure optimal destruction of recovered hydrocarbon vapor and to monitor cleanup progress. Depth to Advanced GeoEnvironmental,Inc.