Soil Vapor Extraction Pilot to Prevent Vapor Intrusion - Preliminary Results

摘要

Soil vapor extraction (SVE) is widely used to remediate volatile organic compounds (VOCs) from soil. In SVE vacuum blowers and wells screened across the vadose zone are used to extract VOCs from unsaturated soil. Practitioners have postulated that this applied vacuum could reduce or prevent vapor intrusion (VI) into nearby buildings - similar to subslab depressurization (SSD) technologies. Conceptually SVE could prevent VI through multiple mechanisms: depressurization across the slab, lowering soil gas concentrations, removal of vadose zone sources, and/or interception of VOCs migrating from groundwater. Although SVE is well established for cleaning up VOC-contaminated soil, and has been applied to control VI, its applicability to VI needs further refinement and validation. Also, SVE engineering offers established monitoring/modeling techniques that may be useful for VI assessments. To investigate and further develop the application of SVE to VI, EPA has funded an SVE pilot study to investigate and optimize how SVE works to control and mitigate VI and to begin to assess whether SVE could serve as a viable neighborhood scale VI mitigation technology. Study objectives include 1) monitoring the effectiveness of the SVE system in reducing/preventing VI in 7 neighboring buildings; 2) determining how long the SVE system needs to be operated to achieve "remedial success" from both the SVE and VI perspectives; 3) determining how far this SVE system can prevent VI in neighboring buildings and the percent reduction of VOCs in indoor air; 4) determining how SVE rebound tests influence VI and whether they provide mass flux measurements useful for VI assessments; and 5) comparing SVE costs over time with conventional SSD. To achieve these objectives, a pilot study was designed employing 10 indoor and 10 subslab locations, along with external soil gas and groundwater samples. Initial results are promising for VOC mass removal and the influence of SVE on subslab soil gas and indoor air.