An official website of the United States government.

We've made some changes to If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Polluted Runoff: Nonpoint Source (NPS) Pollution

Spreadsheet Tool for Estimating Pollutant Loads (STEPL)

The 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).
On this page:


STEPL provides a user-friendly Visual Basic (VB) interface to create a customized spreadsheet-based model in Microsoft (MS) Excel. It computes:

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)HelpUniversal Soil Loss EquationAn equation used to predict the average rate of erosion of an area on the basis of the rainfall, soil type, topography, and management measures of the area. 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.

Top of Page

Model Download and Documentation


(Last updated: 03/15/2018)

Note: This update includes new BMP types (cropland and pastureland) and this version of STEPL has been upgraded to be compatible with Windows 10 and Excel 2016. It is also compatible with Windows 7 and Excel 2013.

STEPL 4.3b

(Last updated: 01/16/2017)

  • STEPL 4.3b Installation Package (.zip) - Note: This download contains a 'setup.exe' file that installs STEPL version 4.3 for full functionality on a customizable number of watersheds; however, it requires Administrator Rights for model installation.

Note: This version of STEPL has been upgraded to be compatible with Windows 10 and Excel 2013.

Input Data Server for STEPL

The Input Data Server for STEPL uses the ArcGIS Viewer for Flex 2.1. You must have Adobe Flash Player version 10.1 or higher installed to use the data server.

Key features of this data server include:
  • More stable GIS platform using a simple and modern Web 2.0-style user interface.
  • Additional map layers:
    • Street map.
    • Aerial map.
    • Elevation map.
    • Boundaries and places.
    • State and County boundaries.
    • Watershed boundary dataset (HUC12, HUC10, HUC8, HUC6, HUC4, and HUC2).
    • NHDplus catchments.
    • NHDplus flowlines and waterbodies.
  • Updated datasets:
    • 2011 Landuse area distribution at the Subwatershed (HUC12) level.
    • 2012 Agricultural animal count at the Subwatershed (HUC12) level.

Top of Page

Training Materials

Top of Page