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Impaired Waters and TMDLs

Opti-Tool: EPA Region 1's Stormwater Management Optimization Tool

Opti-Tool is a spreadsheet-based optimization tool designed to assist stormwater (SW) managers and consulting engineers in preparing technically sound and cost-effective watershed SW management plans to achieve needed pollutant and volume reductions more affordably from developed landscapes throughout the New England Region*. The user-friendly tool is highly flexible with options to conduct both watershed-wide planning level analyses as well as detailed site specific analyses. Output from the Opti-Tool allows users to evaluate costs of various treatment options including the optimized best mix of structural Green Infrastructure (GI), Low Impact Development (LID) and other common categories of SW controls in a targeted geographic area. Opti-Tool is based on extensive research and modelling, makes use of EPA's SUSTAIN decision support system and incorporates best available information for estimating regional* long-term cumulative pollutant load and runoff volume reduction performances for 11 categories of structural SW controls. Other features of Opti-Tool include:

  • Allow the user to interact with the Excel platform for data input, and to direct Excel to call the external SUSTAIN module to simulate GI/LID/SW control performance for a user-selected time period, and provide optimization at a given assessment point in the watershed;
  • Automatically retrieve the optimization results and generate tradeoff curves between total SW control costs and the designated stormwater control targets (either pollutant load-based, or cost-based);
  • Incorporates best available information on SW runoff nutrient quality, including build-up/wash off processes, especially important in New England where storms are predominantly small events (e.g., 50% < 0.3 in.; 70% < 0.6 in.; 80% < 0.8 in.; and 90% < 1.2 in.);
  • Incorporate representative long-term time series of hourly runoff flow and selected pollutant concentrations, as well as regionally-calibrated GI/LID/SW control performance model parameters for total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), and Zinc (Zn); and
  • Provide regionally representative unit cost information as well as estimates of the level of effort (hours) for operation and maintenance of the selected SW controls.

*The Opti-tool can be easily adapted for use in other regions and locations.

  • A companion utility has been developed to allow users to develop input flow and pollutant load input files suitable for Opti-Tool using regional or local climatic data. The Utility is included as part of overall Opti-Tool package that can be downloaded, below.
  • Flow and pollutant load time series outputs from other watershed modelling applications already developed can be readily modified as input to Opti-Tool for conducting stormwater management optimization analyses.

For general questions, and to give us feedback or suggestions about the tool, please contact Mark Voorhees at ( We regret that we are not able to provide detailed technical assistance at this time.