ARCHIVED REPORTS_XR0012524 - Laserfiche WebLink

Home Browse Search

r05 May 1997 AGE-NC Project No 95-0173 ' Page 14 of 29 ' 714 Feasibility The radius of influence for SVE is generally defined as the distance from an extraction well at which a vacuum of at least 0 1 inches of water is observed (EPA - A guide for Corrective Action Plan Reviewers) Generally, a vacuum of at least 0 10 inches of water is required to successfully volatilize subsurface hydrocarbons A vapor extraction feasibility test was performed at the site in July 1997 ' Based on a semi-logarithmic plot of induced vacuum measurements collected during the SVE pilot test from VW-1, VW-2 and MW-3 versus their distances to VW-1 (extraction well), a theoretical radius of approximately twenty-eight feet is estimated at a vacuum of 0 1 inches of water(Figure 3) ' Based upon the results of the pilot test, it appears that SVE would be an effective remediation alternative for soil at the site ' Based on the guide How to Evaluate Alternative Cleanup Technologies For UST Sites (October 1994)published by the United States Environmental Protection Agency (EPA) Office of USTs, the two most important factors that determine the effectiveness of SVE are permeability of the soil and 1 volatility of the contaminant The guide further states that intrinsic permeability between the magnitude of 10'2 and 10' and general volatility for gasolines are generally adequate for SVE • technology (Exhibit II-6 Intrinsic Permeability And SVE Effectiveness) Based on information gained through fate evaluation laboratory analysis, the average permeability at the site was approximately 5 X 10' Results of the fate evaluation laboratory analysis indicated permeability ' conditions at the site are adequate for SVE Based on geologic cross sections(Figures 3 and 4), soil beneath the former UST area has a relatively ' high sandy silt content in the upper thirty-five feet, potentially making SVE an effective remedial method in the vadose zone ' One negative aspect of SVE is that not all contaminated zones of soil are remediated effectively or at the same rate For example, a sandy soil zone will cleanup more quickly than a silty one SVE is not usually effective in soil with high clay content Other drawbacks of SVE include ineffective ' treatment of soil lying below ground water or within the capillary fringe or "smear" zone and ineffective treatment of longer-chain hydrocarbons Ground water remediation may have to be conducted concurrently with SVE to facilitate remediation of the smear zone 4 715 Duration Cleanup penods for soil vapor extraction typically range from several months to several years Based upon the volume of impacted soil,hydrocarbon concentrations and the presence of finer-grained soils ' (silty sands, sandy silts and clayey silts) at the site, 12 to 24 months are estimated for the duration of remediation ' Advanced GeoEnvironmental,Inc. 1