It estimates the depth of the center of mass of a non-polar chemical as a function of time after application. It also calculates the relative amount of chemical in the soil profile as a function of time. The model assumes that chemicals move only in the liquid phase in response to soil-water movement. All of the water in the soil is active in the flow process. Water already in the profile is pushed ahead of the inflowing water in a piston-like manner.
Water is lost from the root zone by evapotranspiration and deep percolation.
Movement of the chemical is retarded by its sorption on the solid soil surfaces. The linear, reversible, equilibrium model is used to describe this sorption process. Dispersion of the chemical is ignored. The soil profile can be divided into 20 layers with different properties in each layer. Soil and chemical properties are uniform within a layer.