High‐Frequency Continuous Monitoring to Track Vapor Intrusion Resulting From Naturally Occurring Pressure Dynamics

Abstract

Vapor intrusion characterization efforts can be challenging due to complexities associated with background indoor air constituents, preferential subsurface migration pathways, and response time and representativeness limitations associated with conventional low‐frequency monitoring methods. For sites experiencing trichloroethylene (TCE) vapor intrusion, the potential for acute risks poses additional challenges, as the need for rapid response to exposure exceedances becomes critical in order to minimize health risks and associated liabilities. Continuous monitoring platforms have been deployed to monitor indoor and subsurface concentrations of key volatile constituents, atmospheric pressure, and pressure differential conditions that can result in advective transport. These systems can be comprised of multiplexed laboratory‐grade analytical components integrated with telemetry and geographical information systems for automatically generating time‐stamped renderings of observations and time‐weighted averages through a cloud‐based data management platform. Integrated automatic alerting and responses can also be engaged within one minute of risk exceedance detection. The objectives at a site selected for testing included continuous monitoring of vapor concentrations and related surface and subsurface physical parameters to understand exposure risks over space and time and to evaluate potential mechanisms controlling risk dynamics which could then be used to design a long‐term risk reduction strategy. High‐frequency data collection, processing, and automated visualization efforts have resulted in greater understanding of natural processes such as dynamic contaminant vapor intrusion risk conditions potentially influenced by localized barometric pumping induced by temperature changes. For the selected site, temporal correlation was observed between dynamic indoor TCE vapor concentration, barometric pressure, and pressure differential. This correlation was observed with a predictable daily frequency even for very slight diurnal changes in barometric pressure and associated pressure differentials measured between subslab and indoor regimes and suggests that advective vapor transport and intrusion can result in elevated indoor TCE concentrations well above risk levels even with low‐to‐modest pressure differentials. This indicates that vapor intrusion can occur in response to diurnal pressure dynamics in coastal regions and suggests that similar natural phenomenon may control vapor intrusion dynamics in other regions, exhibiting similar pressure, geochemical, hydrogeologic, and climatic conditions. While dynamic indoor TCE concentrations have been observed in this coastal environment, questions remain regarding whether this hydrogeologic and climatic setting represent a special case, and how best to determine when continuous monitoring should be required to most appropriately minimize exposure durations as early as possible. ©2017 Wiley Periodicals, Inc.

Chlorinated vapor intrusion indicators, tracers, and surrogates (ITS): Supplemental measurements for minimizing the number of chemical indoor air samples—Part 1: Vapor intrusion driving forces and related environmental factors

“…Hosangadi et al. () also showed a strong relationship between indoor air TCE concentrations and subslab‐to‐indoor differential pressure when differential pressure is greater than zero ( r 2 = .6044); however, the study spans less than 10 days in early February and may not be representative of long‐term trends.…”

“…More recently, Hosangadi et al. () reported field observations of short‐term increases in indoor air TCE concentrations and subsurface‐to‐indoor differential pressure following a decrease in barometric pressure at a coastal Department of Defense site. Hosangadi et al.…”

“…More recently, methods that use a high‐volume soil gas sampling approach with continuous monitoring of FID or PID have been developed and employed at chlorinated hydrocarbon sites (Folson, ; McAlary, Nicholson, Yik, Bertrand, & Thrupp, ). Several publications have featured high temporal resolution, direct compound‐specific measurements of CVOCs with on‐site gas chromatographs (Holton et al., ; Hosangadi et al., ; Kram et al., ; U.S. EPA, , ).…”

Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated‐Solvent Plume Site

“…Assessment of the vapor intrusion (VI) pathway generally follows a multiple‐lines‐of‐evidence (MLE) approach utilizing indoor air, subsurface soil gas, and groundwater concentration data, and consideration of subsurface characteristics and screening‐level modeling (ITRC ; NJDEP ; USEPA , ). It is known that volatile organic chemical (VOC) concentrations in indoor air and soil gas change with time (Folkes et al ; Luo ; Holton et al ; Johnson and Gibson ; Hosangadi et al ), reflecting changes in building dynamics, for example, bi‐directional subslab (SS) soil gas‐indoor air exchange; indoor–outdoor temperature difference; wind speed; heating, ventilation, and air conditioning operation (Hubbard et al ; Luo ; Yao et al ; Holton et al ; Shirazi and Pennell ); and VOC emission flux from groundwater. In theory, changes in VOC flux to indoor air can result from changes in soil properties (e.g., moisture due to precipitation), reaction along the subsurface transport pathway, and changes in groundwater concentration and separation distance (Lowell and Eklund ; Abreu and Johnson ; Tillman and Weaver ; Bozkurt et al ; Shen et al ; USEPA ).…”

Vapor Intrusion Monitoring Method Cost Comparisons: Automated Continuous Analytical Versus Discrete Time-Integrated Passive Approaches

“…Recent innovative developments have resulted in significantly reducing time and cost elements for continuous monitoring. These include multiplexing (allowing for monitoring up to 30 data collection points [DCPs] with a single device) and integration with automation software to not only collect and rapidly analyze samples (e.g., within minutes of collection) but also to instantly visualize results through a web browser and trigger alerts and responses within a few seconds of detection of a risk threshold exceedance (Hosangadi et al., ; Kram, , 2016). These technological advances have significantly reduced costs previously attributed to discrete time‐integrated sampling, laboratory analysis, and labor‐intensive consultant data‐processing and ‐reporting requirements.…”