Numerical Modeling of the Effect of Immobile Water Content on Nitrate Transport in an Unsaturated Porous System

Nitrate originating from wastewater applied on agricultural sites, is one of the most common pollutants in groundwater. It causes a prime risk for human health during the consumption of nitrate contaminated groundwater. In this present study, a numerical model is developed to understand and forecast the fate and transport of nitrogen species in an unsaturated porous media.In addition, the concept of mobile-immobile water content in an unsaturated zone is incorporated in the one-dimensional numerical model for nitrogen species transport. The mass transfer of contaminant in mobile-immobile zone is effectively carried out to predict the concentration of nitrogen species in unsaturated zone. The numerical results of water flow and contaminant transport model in unsaturated zone developed for this study have been validated with the available analytical/numerical solution. Results indicate that the immobile water content plays a predominant role in nitrogen species transport in an unsaturated zone. The simulation results also suggest that nitrogen species concentration travels to a low depth in mobile water zone compared to the immobile water content due to the exchange of contaminant mass from mobile phase to immobile phase. Moreover,the numerical results suggest that the mass transfer rate is an influencing parameter in the movement of ammonium nitrogen and nitrate nitrogen concentration in an unsaturated zone.