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Spreadsheet
Tool for Estimating Pollutant Load (STEPL) employs simple algorithms to calculate nutrient
and sediment loads from different land uses and the load reductions that
would result from the implementation of various best management practices
(BMPs).STEPL provides a user-friendly Visual Basic (VB) interface to create
a customized spreadsheet-based model in Microsoft (MS) Excel. It computes
watershed surface runoff; nutrient loads, including nitrogen, phosphorus,
and 5-day biological oxygen demand (BOD5); and sediment delivery based on
various land uses and management practices. For each watershed, the annual
nutrient loading is calculated based on the runoff volume and the pollutant
concentrations in the runoff water as influenced by factors such as the
land use distribution and management practices. The annual sediment load
(sheet and rill erosion only) is calculated based on the Universal Soil
Loss Equation (USLE) and the sediment delivery ratio. The sediment and
pollutant load reductions that result from the implementation of BMPs are
computed using the known BMP efficiencies.
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Region 5 Model is an Excel workbook that provides a gross estimate
of sediment and nutrient load reductions from the implementation of
agricultural and urban BMPs. The algorithms for non-urban BMPs are based on
the "Pollutants controlled: Calculation and documentation for Section
319 watersheds training manual" (Michigan Department of Environmental
Quality, June 1999). The algorithms for urban BMPs are based on the data
and calculations developed by Illinois EPA. Region 5 Model does not
estimate pollutant load reductions for dissolved constituents.
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