How Does the Periodic Groundwater Table Fluctuation Impact on Chlorinated Vapor Intrusion?

Abstract

Periodic groundwater table fluctuations are found frequently in natural aquifers due to sea tides or seasonal recharge. However, their impact on the transport of volatile organic compounds in the vadose zone released from a groundwater contaminant source (i.e., vapor intrusion) has not been well known. A 2D numerical model was developed to explore vapor intrusion processes in the sandy vadose zone, subject to a fluctuating groundwater table with a range of fluctuation amplitudes and periods. A carcinogenic compound, Trichloroethylene (TCE), was chosen as the groundwater contaminant of interest in the current study and assumed to transport into the dwelling through a crack at the corner of the basement. Results showed that the resistant effect caused by high soil moisture contents in the thin capillary fringe is weakened by periodic groundwater table fluctuations, resulting in a higher concentration of gaseous TCE at the building foundation crack, in comparison with that under a static groundwater table. The increase of the gaseous TCE concentration was induced by the enhancement of diffusion and advection due to groundwater table fluctuations. Sensitivity analyses indicated that a higher amplitude and frequency of fluctuations lead to a higher TCE concentration at the crack under the dynamic equilibrium condition. Specifically, compared with the static groundwater table condition, the TCE concentration at the crack increased by one order of magnitude under the condition of groundwater table fluctuations with an amplitude of 0.2 m and a period of one day. The results obtained could provide insights into the importance of the amplitude and frequency of groundwater table fluctuations on vapor intrusion.

A Critical Review of Groundwater Table Fluctuation: Formation, Effects on Multifields, and Contaminant Behaviors in a Soil and Aquifer System

“…Behaviors of nitrogenous compounds and VOCs during GTF. , With the synergistic effects of microorganisms and oxygen content, nitrogenous compounds undergo nitrification and denitrification in unsaturated soil and saturated aquifers. ,,, VOCs migrate into the surface environment by virtue of the capillary fringe and air–water interfaces. − …”

“… The emission of VOCs is dominantly enhanced by the dynamic changes in groundwater diffusion and advection due to GTF. , The emission pathway length of the PCE is determined by the water table depth and amplitude of GTF, and the fluctuations of PCE emissions lag obviously behind GTF due to the damping effects of both the capillary fringe and soil sorption . Additionally, the effect of the capillary fringe was weakened by periodic GTF, a higher concentration of gaseous TCE in fractures appeared in the changing groundwater table compared to that in a stable state, and the concentration of gaseous TCE increased with the amplitude and frequency of fluctuations . A field investigation showed that GTF shortened or lengthened the transport pathway of VOCs and carried dissolved contaminants to unsaturated soil, which enhanced the volatilization potential of VOCs …”

“…120 Additionally, the effect of the capillary fringe was weakened by periodic GTF, a higher concentration of gaseous TCE in fractures appeared in the changing groundwater table compared to that in a stable state, and the concentration of gaseous TCE increased with the amplitude and frequency of fluctuations. 165 A field investigation showed that GTF shortened or lengthened the transport pathway of VOCs and carried dissolved contaminants to unsaturated soil, which enhanced the volatilization potential of VOCs. 166 The capillary fringe in the vadose zone promotes the redistribution of VOCs, and the location of VOCs is a primary factor affecting their release and migration (Figure 4).…”

“…GTF causes VOC flux levels to increase by >1 order of magnitude in a simulated sandy aquifer, and a larger fluctuation amplitude causes a larger VOC flux (Figure ). The emission of VOCs is dominantly enhanced by the dynamic changes in groundwater diffusion and advection due to GTF. , The emission pathway length of the PCE is determined by the water table depth and amplitude of GTF, and the fluctuations of PCE emissions lag obviously behind GTF due to the damping effects of both the capillary fringe and soil sorption . Additionally, the effect of the capillary fringe was weakened by periodic GTF, a higher concentration of gaseous TCE in fractures appeared in the changing groundwater table compared to that in a stable state, and the concentration of gaseous TCE increased with the amplitude and frequency of fluctuations .…”

New Perspective on the Mobilization of Microplastics through Capillary Fringe Fluctuation in a Tidal Aquifer Environment

“…Haberer et al, 22 meanwhile, experimented with a periodically changing boundary and found that, compared with steady-state conditions, highly dynamic variation of the water table enhances the mass transfer of oxygen from the atmosphere into the groundwater. Zhang et al 23 found that the concentration of trichloroethylene at cracks increased 1 order of magnitude compared with that at a static groundwater table when the groundwater table fluctuated by 0.2 m and a duration of 1 day.…”