SITE INFORMATION AND CORRESPONDENCE

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;t r 10 March 2000 AGE-NC Project No. 95-0137 Page 2 of 3 Estimated Volumetrics: 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 soil addressed by the remediation system is estimated to be 645 cubic meters based on the limited lateral extent of the vadose zone contamination and a depth to ground water or 17 feet to 20 feet below surface grade. The pore-volume exchange was estimated to be 0.47 pore-volumes per day. The pore-volume exchange (E) was estimated on a flow rate of 200 standard cubic feet per minute (scfm) for the overall soil vapor extraction system using the equation: E=25%porosity X 645 m31339.8 m'vapor/hour= 0.47 pore-volumes per day. Locally, the pore-volume exchange rate may vary due to variation of individual well-flow rates selected 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 (sand) and fine-grained (silt) soil and the possible fluctuation of ground water elevation at the site, a general clean-up rate, based on the pore-volume exchange in the inhomogeneous 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 ground water elevation changes over the remediation period. _tel 1l111tlmai` 0 .7ate ti)f 200 SC11i i5 prvYOstd fist till soil rem;dlatiCil l,:1t1.^,orof 211C COrleitl`r'C iilC3ac 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 coarse grained soil. Due to the inhomogeneous stratigraphy of the RFS site, 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. Advanced GeoEnvironmenw,Inc.