Modeling Fate and Transport of Contaminants in the Vadose Zone: Vapor Intrusion and Nitrate-N Leaching Under Future Climate Scenarios

摘要

Understanding and predicting water flow and contaminant transport through the vadose zone is one of the major challenges in the field of hydrology. Lack of experimental data and theoretical understanding about the vadose zone has prevented accurate calculations of water flow and solute transport in this zone and reduced the efficiency of water management practices. Throughout the past few decades, conceptual and mathematical modeling approaches have been applied as useful tools to describe the complex process of flow and transport influenced by physical, chemical, and microbiological interactions within the vadose zone.;In this work, three-dimensional numerical models were developed to simulate water flow and solute transport in variably saturated porous media and were integrated with well-controlled field measurements to validate their performance.;This dissertation has two major parts. In the first part, the goal was to develop a 3-D numerical model to quantify vapor intrusion pathways into a slab-on-ground building under different pressure and ventilation site conditions. Mechanisms controlling vapor intrusion pathways were identified through comparisons between modeled and measured indoor air concentration, subsurface contaminant and oxygen distribution profiles, and diffusive and advective fluxes. The dependency on oxygen concentration in the biodegradation modeling was found to be very important to describe the biodegradation of volatile hydrocarbons.;In the second part, effects of climate change on the fate and transport of nitrate-N beneath a center pivot-irrigated corn field were evaluated. This study utilized a rich historic data set collected from 1993 to 1996 to develop a 3-D numerical model based on realistic sediment lithology to simulate water flow and nitrate transport in the variably saturated porous media. Using this model, future groundwater nitrate-N concentration was predicted from 2057 to 2060 using future climate data. Future groundwater recharge was predicted to decrease at the study area compared to the average historical groundwater recharge data. Nitrate-N leaching was predicted to decrease under the future climate scenario due to increasing evapotranspiration and decreasing mineralization rates.