A new approach in Modeling Colloid Transport in unsaturated porous media under transient flow

Colloid transport models have typically assumed colloidal particles to be in two or three phases including mobile in porewater, immobile and attached to soil grains, or trapped into the air-water interface in case of the presence of unsaturated porous media. However, new studies show that in transient flow conditions, new pools of colloidal particles become availableas a result of the additional shear stress due to higher flow rates (e.g. Lehart and Saiers 2003). This behavior has typically been modeled by considering the detachment rate as a function of the flow rate. However, this approach does not take into account new sources of colloidal particles becoming available for detachment as a result of higher flow rates. In this research, a new modeling approach is presented in which immobile colloidal particles are considered to be in multiple domains in terms of their availability for detachment. For this purpose, the rate of detachment of colloidal particles in each domain is considered to be a function of the flow rate and the functional forms of the relationships between the release rates of colloidal particles are considered such that the immobile colloidal domains corresponding to lower availability for detachment only becomes available at higher flow rates. This model also considers the rate of capture of colloidal particles by the soil grains to be a function of flow rate. The model is validated and calibrated using the data published by Lehart and Saiers,2003 and shows good agreement between the model prediction and the observed data.