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The major disadvantage regarding the two ground-water remediation techniques discussed in the <br /> preceding paragraphs is the high cost associated with the installation and operation of each. In <br /> addition, pumping-and-treating in concert with air-sparging is effective when operating in <br /> conjunction with soil-vapor extraction. Since soil-vapor extraction is not recommended, pump- <br /> and-treat/air-sparging technologies are also not recommended at Village West. <br /> Intrinsic remediation involves quantifying hydrocarbon removal as a result of naturally-occurring <br /> attenuation by in-situ microbes. A site is monitored for a period of time, six months to several <br /> years, if needed, in order to determine the rate at which naturally-occurring microbes are <br /> removing hydrocarbons from impacted ground water and saturated zone soil. Plotting a <br /> stationary plume configuration will yield a first-order rate constant, which can be used to <br /> >' determine the time required for removal of hydrocarbons from the impacted ground water. This <br /> technique is usually employed in conjunction with source removal to stem continued hydrocarbon <br /> migration into the saturated zone. Intrinsic remediation can be extremely cost-effective for sites <br /> which exhibit less than 5000 µgIf of TPH-g, less than 500 µg/f of benzene, slow migration, and <br /> a remediation schedule where time is not overly critical. Current available field data and the <br /> site setting of Village West indicate that intrinsic remediation would be cost-effective in cleaning <br /> i`- up hydrocarbons adsorbed in the saturated zone. Microbes designed and grown specifically to <br /> alleviate gasoline impaction might be added to enhance the cleanup process. Irwin recommends <br /> intrinsic remediation for Village West. <br /> So, based on all known site data and the preceding discussion, soil bioventing and intrinsic <br /> remediation have been selected as the best available alternatives to remediate soil and ground <br /> water impaction, respectively, at Village West. <br /> REMEDIATION SYSTEM DESIGN <br /> As previously stated, W.W. Irwin, Inc. recommends in-situ bioremediation using bioventing and <br /> intrinsic remediation to remediate hydrocarbon-impacted soils and hydrocarbon-impacted ground <br /> water underlying Village West. Irwin recommends conducting an in-situ respiration test, <br /> installing five bioventing wells at locations depicted in Figure 4. The wells will be used to inject <br /> atmospheric air into the subsurface. The proposed wells will be screened from approximately <br /> 5 to 15 feet below surface grade (bsg). Detailed remediation system engineering design will be <br /> initiated upon completion of the in-situ respiration test data analysis. <br /> -_l <br /> W.W. Irwin, Inc. <br /> _ 1 Project No. 33016.07 <br /> December 1995 8 <br /> I'`I <br />