Flow and transport in the vadose zone: Soil atmosphere boundary and capillarity effects

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Over the past few decades our ability to understand and model flow and transport processes in the vadose zone (subsurface above the groundwater table) has increased considerably. Evidence from the literature suggests, that a large number of conceptual models have been developed which can be translated to numerical models to study the transient variably saturated water flow, heat and solute transport in the vadose zone. This research aims to develop new and validate existing conceptual and numerical models for: (1) coupling of physical and chemical processes, and (2) integration of surface and subsurface processes. The crux of this research is to quantify the effect of soil-atmosphere boundary and concentration dependent capillarity on flow and transport in the vadose zone via interfacial phenomena. These phenomena have considerable influence on many geotechnical and geoenvironmental designs. This research will improve our understanding of the coupled, non-linear, physical and chemical processes operative in the vadose zone to improve our design capabilities. It is proposed to achieve this goal via a number of related studies, each with its own specific objectives. Design application 1. This study aims to quantify the effect of climate change on behavior of expansive soils also known as swelling and shrinking soils. These soils go through large volume change, with changes in soil water content. Climate is the primary factor that affects the behavior of expansive soils. Most of the populated area of prairie Canada is covered with thick glacial deposits that are expansive in nature. Shallow foundations and infrastructure (buried pipelines) in the city of Regina and Winnipeg have a long history of being affected by the swelling and shrinkage of expansive soils and will benefit from this research. Design application 2. As the climate change puts more pressure on the existing water resources, the use of grey water (GW) for irrigation and aquifer recharge is becoming increasingly common. GW refers to household wastewater form laundry and kitchen and contains large quantities of surfactants. Capillarity is the primary force that enables the soil to retain water and regulates its movement. GW effects capillarity by changing the interfacial properties such as surface tension and contact angle. This research will enhance our understanding of the fundamental processes in the flow and transport of GW in vadose zone. Design application 3. Soil covers are an important part of any waste management facility. A soil cover can be viewed as a thin interface placed between the atmosphere and the underlying waste. They separate the toxic waste from the atmosphere and climate is a primary design variable. They are expected to be functional for very long periods and are highly likely to be affected by climate change. The objective of the research is to develop design guidelines for soil covers by integrating the surface and subsurface processes.