Groundwater Nitrate Contamination Risk Induced by Irrigation from Polluted River Water

Groundwater contamination experiments using irrigation water from the polluted Kuihe River were conducted at the Hanwang hydrological field station, near Xuzhou City. As part of this study, a numerical model was developed on the basis of a mathematical equation with a finite-difference approximation. The model is capable of simulating nitrogen transformation processes during subsurface transport. Numerical simulations were conducted to estimate nitrogen species concentrations along a flowpath during irrigation. Because of the complex field irrigation conditions, uncertainties of the model input parameters were analyzed and probability density functions (PDFs) of the model input parameters were constructed using the available field data or professional judgement. The PDFs and a Monte Carlo simulation technique were used in this study for the evaluation of risk of groundwater contamination. The results of this study demonstrated that the nitrate mass leaching into groundwater with a 25 and 75% probability would be no less than 0.46 and 0.27 times that in irrigation water, respectively, when the Kuihe River irrigation water was used for the first day and clean drinking water was used in the next $30\text{days}$ . Therefore, utilization of the polluted Kuihe River water for irrigation would likely result in groundwater nitrate contamination.