How 2NFORM Calculates Runoff and Pollution Reductions

This article explains how 2NFORM uses your stormwater program data to quantify runoff and pollutant load reductions in a way that is consistent, transparent, and defensible.

In this article:

• Overview
• What Data Goes In
• How TELR Processes the Data
• What You Get Out
• Why It’s Useful
  
  

Overview

2NFORM, powered by the TELR model, transforms the stormwater program data you already collect into measurable reductions of runoff and pollutants. By systematically applying your structural and non-structural practices to a modeled baseline, TELR shows how much cleaner your MS4’s discharges are today (current condition) and what could be achieved with planned improvements (potential condition).

This approach gives municipalities a consistent and repeatable way to measure progress toward compliance targets, including TMDL wasteload allocations, while also supporting local planning and investment decisions.

What Data Goes In

2NFORM is prepopulated with relevant local and regional datasets necessary to defensibly estimate stormwater runoff and pollutant load generation.

• Landscape and hydrology data (applied automatically via TELR):
  
  • Rainfall, soils, land cover, impervious surfaces
  • Empirical pollutant concentrations by land use

2NFORM pulls the information you collect and manage in your compliance workflows that improve stormwater quality and reduce negative impacts.

• Non-structural practices (entered via inspections & maintenance modules)
  
  • Street sweeping
  • Catch basin cleaning
  • Impervious disconnection and other good site design applications
• Structural BMPs (from asset inventories and inspection data):
  
  • Decentralized green infrastructure (i.e. bioretention, infiltration features, permeable pavement, etc)
  • Centralized or regional treatment facilities (i.e Detention basins, wet ponds, infiltration basins etc)
    
    

How TELR Processes the Data

TELR applies a systematic, grid-based accounting framework:

1. Start at the baseline. Calculate runoff and pollutants as if no practices were in place.
2. Apply non-structural BMPs first. Adjust pollutant loads (e.g., cleaner streets = lower runoff concentrations).
3. Route runoff through structural BMPs. TELR models water movement across the 30m grid, sequentially routing flows through decentralized controls upstream into larger centralized systems downstream.
4. Apply nationally derived treatment performance. Structural BMP performance is matched with effectiveness curves based on scientific literature and available recent asset condition assessments.
5. Account for drainage connectivity and timing. Catchment and drainage runoff and pollutant loading estimates are aggregated and summarized, adjusting where necessary for connectivity to receiving waters.

What You Get Out

2NFORM presents the results in clear formats designed for program managers:

• Runoff volume reductions — how much less water is discharged from each catchment and drainage as a result of land and stormwater management practices..
  
  
• Pollutant load reductions — how much cleaner the water is discharged from each catchment and drainage.
  
  
• Scenario comparisons — ability to compare the current progress from existing investment with the future potential reductions should planned investments be implemented.
  
  
• Maps, charts, and tables — reductions by stormwater asset, treatment practice, catchment drainage, and city-wide totals.
  
  

Why It’s Useful

• Compliance. Provides the numbers to evidence progress toward MS4 and TMDL requirements for any drainage:

  • a defensible baseline of uncontrolled loads,

  • a current loading reflecting actual progress, and

  • a potential loading to forecast the impact of planned controls.

• Transparency. Creates a defensible record of how each practice contributes to outcomes.

• Efficiency. Use mapped runoff and loading to focus resources where risk and reductions are greatest.

• Communication. Converts technical modeling into visuals leadership, regulators, and the public can grasp.

Compliance Note

EPA requires MS4 permits to be consistent with TMDL WLAs. 2NFORM’s TELR-powered accounting supplies the defensible baseline-to-current-to-potential trajectory you need to show progress, track incremental reductions, and build trust with regulators.

If you’d like to talk methods with our science team, contact Support and we’ll connect you.