From the 323 projects listed in U.S. EPA's MTBE Treatment Profiles dataset, 138 projects were identified where MTBE was treated using SVE. Information on the treatment of oxygenates other than MTBE during these 138 projects is limited. Two projects reported treating these other oxygenates: one project reported TBA and one reported ethanol.
Most of the 138 SVE projects were full scale (137 projects). In addition, most of the projects used SVE in conjunction with air sparging (74 projects) or SVE alone (20 projects); the remaining projects supplemented SVE treatment with bioremediation, ISCO, pump-and-treat, or multiple technologies.
The 138 SVE projects primarily used vertical wells; three projects used horizontal wells. Of the 23 projects for which information about the number of SVE wells was available, 20 used 2-8 wells per project, with an overall range of 1-16 wells. Of the 74 projects that used air sparging with SVE, the number of SVE wells used ranged from 1 to 23 wells per project, with 30 projects in the range of 2-5 wells per project. Four of these 74 projects reported the type of air emission treatment used, with two reporting use of GAC, one of catalytic oxidation, and one of thermal oxidation. Eight of the SVE projects reported the types of aboveground treatment technologies that were employed to treat off-gas containing MTBE and other oxygenates. For seven of these eight projects, thermal treatment was employed; six projects used catalytic oxidation and one project used thermal oxidation. One of the projects used catalytic oxidation and another project used GAC adsorption to treat the SVE off-gas.
24.5.5 Performance of SVE in Treatment of Oxygenates
Several approaches have been used to evaluate SVE performance for MTBE treatment, including analyzing the changes in MTBE concentrations in soil, soil vapor, or groundwater, or estimating the mass of contaminant removed. SVE is used to reduce the mass of contaminants that may leach or otherwise migrate from the vadose zone to the groundwater. This reduced leaching rate may result in lower concentrations of contaminants in groundwater, and the performance data provided are for MTBE concentrations in groundwater.26
The treatment performance data for the 19 completed projects presented in Table 24.9 show that SVE (either alone or in combination with other technologies) has been used to remediate MTBE in groundwater from concentrations >100,000 to <50 |^g/L and has achieved MTBE concentration reductions >99%. The median project duration for the 19 completed sites ranged from 3 months to 5 years.
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