Development and Application of an ArcGIS-Based Model for Estimating Phosphate Load from OSTDS to Surface Water Bodies

This paper presents the development and validation of the phosphorus reactive transport module within the ArcNLET-Py, which is an ArcGIS-based Nutrient Load Estimation Toolbox written using Python for ArcGIS Pro. ArcNLET-Py was designed to simulate nitrogen transport from Onsite Sewage Treatment and Disposal Systems (OSTDS) to surface water bodies. The new feature of phosphate reactive transport modeling enables ArcNLET-Py to simulate nutrient (nitrogen and phosphorus) reactive transport from OSTDS drainfields to surface water bodies through the vadose zone and groundwater surficial aquifer. ArcNLET-Py was evaluated and validated by using the monitoring data of hydraulic head and nutrient concentrations at the Turkey Creek Sub-Basin of the Indian River Lagoon in Central Florida. An ArcNLET model was developed and calibrated to simulate nutrient concentrations and loads. Results demonstrated that the calibrated ArcNLET-Py model can reasonably simulate the monitoring data. ArcNLET-Py can be used as a valuable tool for assessing and managing nutrient load from OSTDS to groundwater and surface water bodies.