Assessing the Impact of Hydraulic Hysteresis with Air Entrapment Consideration on Water and Salt Transport in the Vadose Zone

ABSTRACT: Brine-produced in oilfields is a major source of saline water, leading to the contamination of soil and groundwater. The interaction of meteoric water and atmospheric evaporative energy with the unsaturated soils controls the water balance at the ground surface, hence dictating the water movement and salt/solute transport in the subsurface. Considering that unsaturated soils typically undergo frequent cyclic drying and wetting events, hydraulic hysteresis, including air entrapment consideration, plays an important role in the movement of water and solutes within the vadose zone. In most instances, hysteresis in hydraulic functions is ignored, and land-climate interaction analysis is carried out, solely by representation of soil water characteristics by either the initial or the main drainage curve, even to represent intermittent cycles of climatic drying and wetting. This research utilizes a variably saturated flow and transport model to study the impact of hydraulic hysteresis on the salt transport in the subsurface using multiyear climate data for varying climatic conditions across the province of Alberta. The hysteretic soil water characteristic curves used for assessment also consider the air entrapment, which is usually excluded in hysteretic analysis. The results show that the inclusion of hysteresis in the land-climate interaction analysis, results in dissimilar solute distributions in the subsurface when compared with non-hysteretic analysis. Furthermore, the relative impact scale of hysteresis on the solute transport is the function of climate type and degree of air entrapment. In addition, the results also show that excluding air entrapment in hysteretic analysis underestimates the advective flux of the solute and can potentially lead to improper assessment of the fate of solute.