Groundwater nitrate pollution risk assessment of the groundwater source field based on the integrated numerical simulations in the unsaturated zone and saturated aquifer.

•A method of assessing groundwater pollution risk in the water source is proposed.•The method integrates models of nitrate fate and transport in the vadose zone and aquifer.•Pollution risk is dominated by the mediate level in the aquifers.•Pollution risk in the confined aquifer is lower than that in the phreatic aquifer.•Groundwater polluted source intensity and nitrate attenuation process affect the risk.