An important aspect of diffuse (nonpoint) pollution transport in the subsurface is the movement of contaminants through the unsaturated zone.

CV-GNLM (Groundwater Nitrate Loading Modeling) and CV-SWAT (Soil & Water Assessment Tool) are two different approaches to estimate nitrate loading leaching rates to groundwater

After the water leaves the root zone, it percolates to the water table, mostly vertically down.  From the water table it travels laterally and vertically through groundwater along groundwater flow paths.