Protecting Off-Site Populations and Site Workers from Vapor Discharges during Shallow Soil Mixing at the North Carolina State University National Priorities List Site

Abstract

Although vapor monitoring is generally a component of remedial action activities, most sites do not have routine gaseous releases or vapor clouds erupting from the soil during implementation of the cleanup process (or during cleanup of the site). At the North Carolina State University Lot 86 National Priorities List Site, over 8410 m³ (11,000 yd³) of chemical waste was disposed at the Site, including organic solvents and shock-sensitive and airand water-reactive compounds. During the Remedial Action, it was imperative to protect site workers and off-site populations from potential inhalation exposures. Engineering controls were incorporated into the shallow soil mixing process to limit the release of gaseous compounds. To quantify potential exposures to on-site and off-site receptors, modeling was conducted to evaluate potential exposure routes and migration pathways. To demonstrate acceptable levels of airborne constituents, a multifaceted air sampling and monitoring program was implemented. To ensure that potential exposures could be quantified, passive dosimeters, continuous real-time monitoring, time-weighted whole air sampling, and grab samples of vapor clouds were all critical components of the air monitoring program. After the successful completion of the Remedial Action, the pre-Resource Conservation and Recovery Act (RCRA) chemical waste generated from the University’s educational and research laboratories was entirely encapsulated and neither on-site workers nor off-site populations were exposed to analyzed compounds above any health-based action level (i.e., 15-min short-term exposure limit [STEL], 8-hr threshold limit value, or time-weighted average permissible exposure limit)