Simplified Model of Nitrogen Transformation and Transport

The simplified model consists of three components (flow model, transport model, and nitrogen (nitrate (NO3) and ammonium (NH4)) load estimation) implemented in six separate modules as follows:

  • The proto-module (0-Preprocessing) aids in preparing soil datasets derived from the Soil Survey Geographic Database (SSURGO), which includes hydraulic conductivity, porosity, texture, and spatial distribution.

  • The first module (1-Groundwater Flow) consists of a simplified flow model that uses smoothed topography to approximate the water table and calculate the magnitude and direction of groundwater seepage velocity.

  • The second module (2-Particle Tracking) calculates flow paths based on the first module’s results of velocity direction and magnitude results.

  • The third module, the Vadose Zone MODel (3-VZMOD), is optional and estimates the vertical soil flow and nitrification and denitrification of ammonium (NH4) and nitrate (NO3) within the Vadose Zone below the OSTDS based on the number of OSTDS points, soil conditions, and depth between the drainfield and the water table.

  • The fourth module (4-Transport) uses an analytical solution to the advection-dispersion equation to simulate the movement of NH4 and/or NO3 plumes. The Transport Module warps plumes along their paths.

  • The fifth module (5-Load Estimation) calculates the NH4 and/or NO3 mass load-input, -output, and -removal for both surface water bodies and plumes that fall short of water features.

The modules are each described in detail below.

Subsections: - 0-Preprocessing for preprocessing steps. - 1-Groundwater Flow for understanding groundwater flow. - 2-Particle Tracking on particle tracking. - 3-VZMOD for vertical zone modeling. - 4-Transport for transport modeling. - 5-Load Estimation for load estimation techniques.