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10 April 2000 AGE-NC Project No. 95-0137 Page 2 of 4 • Toluene with an MCL of 0.15 mg/1 • Ethylbenzene with an MCL of 0.7 mg/l • Xylene with an MCL of 1.75 mg/1 • MTBE with a secondary MCL of 0.013 mg/l 2.0. ESTIMATED VOLUMETRIC CALCULATIONS The estimate of the mass of soil to be remediated is based on analytical data from soil samples, field observations, field screening data and the inferred lateral/vertical distribution of the contaminant mass in the soil. The hydrocarbon mass in contact with saturated soil (under the water table) will be variable due to natural ground water elevation variation and mechanical effects of air-sparging in the saturated soil. The volume of impacted soil addressed by the remediation system is estimated to be 645 cubic meters based on the limited lateral extent of the vadose zone contamination, the estimated radius of influence of the SVE well network and a depth to ground water of 17 feet to 20 feet below surface grade. The pore-volume exchange was estimated to be 51 pore-volumes per day. The pore-volume exchange (E) was estimated on a flow rate of 200 standard cubic feet per minute (scfrrl) for the overall soil vapor extraction system using the equation: E=25% porosity X 645 rn3/339.8 m3 vapor/hour= 0.47 hours per pore-volume exchanged. E daily= 24 hours/0.47= 51 pore-volumes per day. Note: 200 scfm x 0.02832 meters/fect3=5.664 cubic meters minute x 60 minutes hour=339.8 m3hr Locally, the pore-volume exchange rate may vary due to variation of individual well-flow rates to more effectively address local hydrocarbon concentrations and due to the response of the local soil composition and well-flow capacity. Due to site-specific stratigraphy comprised of interbedded coarse-grained soil (sand) and fine- grained soil (silt) and the probable fluctuation of ground water elevation at the site, a general clean- up rate, based on the pore-volume exchange in the nonhomogeneous soils is difficult to estimate and the mitigation period may be extensive in duration. The process and time period for ground water mitigation may extend well beyond that required for the soil remediation due to saturated soil behavior and variation ground water elevation during the remediation period. Advanced GeoEnvironmentid,Inc.