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27 March 2000 AGE-NC Pi-C ect No. 98-0450 Pagc 7 of' ]9 of the contaminant ]Hass 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 et)ects of air-sparging in the saturated soil_ The volume of soil addressed by the remediation system is estimated to be 2.000 cubic ]peters based on the defined lateral extent of the vadose zone contamination and a depth to ground water ol'45 feet below surface grade. The pore-volume exchange rate was estimated to be 10 pore-volumes per day. The pore-volume exchange (1=.) was estimated on a flow rate of 200 standard cubic feet per minute (selin) for the overall soli vapor extraction system usiM-1 the equation: F— 40% porosity X 2,000 iii' / 339.8 iiV vapor/hour- 2.35 hours per pore-volumes exchange. 1 24 hours per day x 2.35 hours 13er pore-volumes exchange = ]0 pore valume per day 200 sctin N 0.02832 rectlmetcr - i.664 cubic Icc( minute s 60 Minutes hour=339.8 m'hr 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 wclI-floNV capacity. Due to the site stratigraphy comprised of'coarse sand at 40 feet bsg to 55 feet bsg and fine-grained soil (silt) above 40 feet bsg and the possible fluctuation of ground water elevation at the site, a general clean-up rate, based on the pore-volume exchange in the nonhoniogeneous soil is difficult to estimate and the mitigation period may be extensive in duration. The process and time period for ground water mitigation ]nay- extend well beyond that required for the soil remediation due to saturated soil behavior and ground water elevation changes over the remediation period. 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 minimization of'channeling in the fine-grained soil. Due to the nonliotnogcneous stratigraphy of the site, unequal remediation response is anticipated fi-om the soil. in other words, fine grained soil will require a greater quantity of mitigation ener' y, and therefore, a longer time period to meet the corrective action goal for impacted ground water mitigation. IloNvever, ground water occurs within coarse-grained soil and is anticipated to respond well to the remediation effort. -]rhvrvrr°ed Grok:n�irunnrcntat.]nc.