Our hydrologists designed three mass-balance spreadsheet computer models that can be used to quantitatively predict the impact of residual or excess farm-field soil nitrate or mass balance residual on the concentration of nitrate in underlying shallow groundwater.
A version of the model also helps us to back-calculate how much nitrate reached groundwater to produce a particular nitrate concentration reading. All three models allow the user flexibility in defining site-specific model variables.
The report, Spreadsheet Models for Determining the Influence of Land Applications of Fertilizer on Underlying Groundwater Nitrate Concentrations, presents these models and discusses assumptions and limitations. The spreadsheet itself is included as an appendix in the publication summary webpage for this report.
The models are useful as an educational tool, but are not a substitute for actual groundwater field sampling, due to the complexity of chemical, biological, and hydrological reactions in the subsurface.