Citation:

Stewart, L., C. Lutes, R. Truesdale, B. Schumacher, J. Zimmerman, AND R. Connell. Field Study of Soil Vapor Extraction for Reducing Off‐Site Vapor Intrusion. Groundwater Monitoring & Remediation. Wiley-Blackwell Publishing, Hoboken, NJ, 40(1):74-85, (2020). https://doi.org/10.1111/gwmr.12359

Impact/Purpose:

Vapor intrusion has been identified as an important human exposure pathway and people may come into contact with hazardous vapors while performing their day-to-day indoor activities. he challenge of this VI effort was to assess the effectiveness of mitigation systems to reduce or eliminate VI over a wide area (i.e., neighborhood instead of individual home) while at the same time, remove the source of the contamination. A soil vapor extraction (SVE) system was installed and operated at a Superfund site in California. Soil gas and indoor air samples were collected at various times throughout the year from homes and buildings surrounding the site to determine the presence or absence of volatile organic compounds (VOCs). The results of our research will be used to support of updating Regional guidance documents and by OLEM in their initial and updated vapor intrusion guidance documents. Remedial Project Managers are anticipated to use our research results in selecting remedial alternatives at various Superfund sites as well as methods for sampling soil gas and indoor air VOC concentrations.

Description:

Soil vapor extraction (SVE) is effective for removing volatile organic compound (VOC) mass from the vadose zone and reducing the potential for vapor intrusion (VI) into overlying and surrounding buildings. However, the relationship between residual mass in the subsurface and VI is complex. Through a series of alternating extraction (SVE on) and rebound (SVE off) periods, this field study explored the relationship and aspects of SVE applicable to VI mitigation in a commercial/light‐industrial setting. The primary objective was to determine if SVE could provide VI mitigation over a wide area encompassing multiple buildings, city streets, and subsurface utilities and eliminate the need for individual subslab depressurization systems. We determined that SVE effectively mitigates offsite VI by intercepting or diluting contaminant vapors that would otherwise enter buildings through foundation slabs. Data indicate a measurable (5 Pa) influence of SVE on subslab/indoor pressure differential may occur but is not essential for effective VI mitigation. Indoor air quality improvements were evident in buildings 100 to 200 feet away from SVE including those without a measurable reversal of differential pressure across the slab or substantial reductions in subslab VOC concentration. These cases also demonstrated mitigation effects across a four‐lane avenue with subsurface utilities. These findings suggest that SVE affects distant VI entry points with little observable impact on differential pressures and without relying on subslab VOC concentration reductions.

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