Using 2NFORM Analytics to Comply With TMDL Requirements with Confidence

How TELR’s location-specific accounting turns MS4 data into defensible progress toward WLAs.

In this article: 

• TELR Overview
  
• Why TMDLs Matter
  
• How 2NFORM Helps
• The Value for MS4s
• Learn More About The Calculations
• Peer Reviewed Publications
  
  

TELR Overview

2NFORM turns your MS4 program data into clear, defensible accounting of stormwater runoff and pollutant reductions. Powered by the 2NDNATUREs Tool to Estimate Load Reductions (TELR) model, it shows how much your MS4 contributes to regulated receiving waters and how much those contributions decline as practices are implemented. This gives municipalities a credible way to demonstrate progress toward meeting TMDL wasteload allocations (WLAs), set realistic targets, and build confidence with regulators.

Why TMDLs Matter

A Total Maximum Daily Load (TMDL) sets the maximum amount of a pollutant a waterbody can receive while still meeting standards. Each TMDL allocates portions of that allowable load to sources. For MS4s, this is a wasteload allocation (WLA)—your jurisdiction’s share of the reduction needed. EPA requires stormwater permits to be consistent with TMDLs, so permittees must demonstrate reductions aligned with their WLA.

How 2NFORM Helps

2NFORM, powered by TELR, provides the data-driven foundation municipalities need to meet TMDL obligations:

• 30 m grid-based modeling. TELR estimates runoff and pollutant loads at high spatial resolution, capturing soils, land cover, imperviousness, and rainfall patterns across your city.

• Direct linkage to receiving waters. TELR routes runoff from the landscape to structural BMPs and then to outfalls, quantifying the pollutant load delivered from your MS4 to regulated receiving waters.

• Scenario-based accountability. Compare baseline (no practices), current (your actual practices), and potential (planned/optimized practices) for a transparent record of progress and a forecast of what’s achievable.

• Defensible compliance reporting. TELR’s peer-reviewed, spatially explicit methods yield credible, repeatable accounting regulators trust.

The Value for MS4s

• Demonstrate progress. Show reductions in runoff and pollutant loads relative to baseline.

• Meet WLAs with confidence. Align outcomes with TMDL requirements.

• Set realistic targets. Clarify proportional contributions in larger watersheds and establish achievable goals.

• Strengthen regulator relationships. Provide transparent results that build accountability and trust.

Learn More About the Calculations

Go deeper into the TELR methods behind 2NFORM:

• [What Is a Baseline and Why It Matters]

• [How 2NFORM Calculates Runoff and Pollution Reductions]

• [Structural BMP Performance in 2NFORM]

• [Tracking the Impact of Street Sweeping]

Peer-Reviewed Publications

• Beck, N.G., Conley, G., Kanner, L., Mathias, M. (2017). An urban runoff model designed to inform stormwater management decisions. Journal of Environmental Management, 193, 257–269.

• Conley, G., Beck, N., Riihimaki, C.A., Tanner, M. (2020). Quantifying clogging patterns of infiltration systems to improve urban stormwater pollution reduction estimates. Water Research, 100049.

• Conley, G., Beck, N., Riihimaki, C.A., Tanner, M. (2021). Assessing the feasibility of a cloud-based, spatially distributed modeling approach for tracking green stormwater infrastructure runoff reductions. Water, 13, 255.

• Conley, G., McDonald, R.I., Nodine, T., and Beck, N.G.. (2022a). Assessing the influence of urban greenness and green stormwater infrastructure on hydrology from satellite remote sensing. Science of the Total Environment, 817, 152723.

• Nodine, T, Conley, G. Riihimaki, C.A., Holland, C and Beck N.G. (2024) Modeling the impact of future rainfall changes on the effectiveness of urban stormwater control measures. Nature Scientific Reports, 14: 1482.

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