Modeling of Chlorinated VOCs Transport under Dual Bioreactions

Abstract

Once chlorinated volatile organic compounds (CVOCs) are released into the subsurface they are spread out through the porous soil matrix by complicated processes such as advection, dispersion, and sorption. CVOCs can be also biodegraded by indigenous microorganism via aerobic and anaerobic bioreactions, which generate distinct benign or harmful by-products. Heterogeneous subsurface characteristics and non-uniform distribution and consumption of oxygen in the subsurface may allow the dual bioreactions to coexist within a representative subsurface volume (RSV). The portion of each bioreaction within a RSV will depend on multiple factors such as oxygen, contaminant, and microorganism levels. Oxygen can be supplied into the contaminated zone through the dispersive and advective transport of oxygen in gas phase as well as the flow of the groundwater containing dissolved oxygen. As the dual bioreactions are coupled with multiple fluid flows (groundwater and gas) and multispecies transport, the analysis of the bioreactions is very complicated. However, the enhanced understanding of the dual bioreactions of CVOCs is required in accurately predicting the fate and transport of CVOCs at the contaminated sites. This study numerically investigates: the effects of dual bioreactions on the fate and transport of CVOCs in the variably saturated zone; and, the temporal and spatial evolution of bioreaction zones in the domain. Trichloroethylene is selected as a primary contaminant, and its sequential aerobic/anaerobic bioreactions are considered.