Impaired Waters and TMDLs

Impaired Waters and Stormwater

Throughout the United States there are thousands of waters listed for impairments from stormwater sources. The most common pollutants coming from stormwater sources include sediment, pathogens, nutrients and metals. These impaired waters need a Total Maximum Daily Load (TMDL), which identifies the total pollutant loading that a waterbody can receive and still meet water quality standards, and specifies a pollutant allocation to specific point and nonpoint sources.

The TMDL is implemented in part via the National Pollutant Discharge Elimination System (NPDES) stormwater permitting system. States and EPA Regions have used a variety of methods to develop stormwater-source TMDLs during the past decade. With the expansion of NDPES stormwater regulations to smaller municipalities and smaller construction activities, there has been increasing demand for more detailed quantification of stormwater allocations in TMDLs that are more useful for implementation in NPDES permits.

Resources for Developing Stormwater-Source TMDLs

TMDLs to Stormwater Permits Draft Handbook, November 2008
Currently there are thousands of Clean Water Act section 303(d) waters listed as impaired for stormwater-source pollutants such as pathogens, nutrients, sediments and metals. The draft handbook provides a technical reference for TMDL practitioners and permit writers on current methods being used to develop more detailed stormwater-source TMDL allocations, TMDL implementation plans including best management practices, and methods for translating TMDL allocations into NPDES stormwater permit requirements.

Total Maximum Daily Loads with Stormwater Sources: A Summary of 17 TMDLs, July 2007, EPA 841-R-07-002
This document summarizes 17 TMDLs that have been developed for stormwater-source pollutants in 16 states, representing a range of pollutants, models used and different allocation and implementation methods.

Total Maximum Daily Loads and National Pollutant Discharge Elimination System Storm Water Permits for Impaired Water Bodies: A Summary of State Practices, Sept. 15, 2007
This EPA report summarizes information on TMDL-stormwater practices in 10 states, provides specific TMDL and permit language, and identifies some specific technical and programmatic challenges.

TMDL-Stormwater Permit Case Studies:

These two case studies describe activities linking stormwater-source TMDLs currently being developed with applicable stormwater permits:

Innovative TMDLs using Surrogates for Stormwater Pollutants

Three states in EPA Region 1 have developed TMDLs using impervious cover and flow as surrogates for stormwater-source pollutants in streams listed for biological impairment.

Impervious Cover:


Archived Versions of TMDL Webcasts

National Association of Counties (NACo) "Stormwater Runoff for Counties" Webinar, November 12, 2009

This Webinar, with a targeted audience of NACo members and funded in part by EPA, describes how counties protect vital waterways, lakes, ponds and drinking water from pollutants on streets, driveways and roofs.

TMDL-Stormwater Technical Resources

Revisions to the November 22, 2002 Memorandum “Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Stormwater Sources and NPDES Permit Requirements Based on Those WLAs,” November 26, 2014
This memorandum clarifies aspects of EPA’s November 22, 2002 memo regarding water quality-based effluent limitations, disaggregating WLAs in TMDLs and designating additional sources of stormwater.

Incorporating Green Infrastructure into TMDLs
This fact sheet provides examples of how some states describe green infrastructure and low impact development activities in their TMDL implementation sections to address stormwater-source impaired waters.

Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and NPDES Permit Requirements Based on Those WLAs, Nov. 22, 2002
This memo clarifies existing EPA regulatory requirements for, and provides guidance on, establishing wasteload allocations (WLAs) for storm water discharges in TMDLs.

An Approach for Using Load Duration Curves in the Development of TMDLs, Aug. 2007
This document shows how duration curves can be used for developing TMDLs and includes one case study.

Options for Expressing Daily Loads in TMDLs, June 22, 2007
This draft document provides technical options for developing daily load expressions in TMDLs calculated using time frames beyond daily allocations (e.g., annual, monthly, seasonal).

Stressor Identification Guidance Document (PDF) (228 pp, 1.9 MB, EPA 822-B-00-025, About PDF)
This document provides a formal process to identify stressors causing biological impairments in aquatic ecosystems and a structure for organizing the scientific evidence supporting the conclusions.

An online application that helps scientists and engineers in the Regions, States and Tribes find, access, organize, use and share information to conduct causal evaluations related to stressor identification in aquatic systems.

TMDL Model Evaluation and Research Needs, 2005
This document provides a comprehensive review of available models for developing TMDLs.

These short fact sheets for state permitting authorities, municipalities and others describe developing and implementing stormwater management programs and linkage to TMDLs:

Other EPA Stormwater Resources

Nonpoint Source Urban Website. Provides technical information on control of urban nonpoint source pollution.

Stormwater Program. Contains technical and regulatory information on the NPDES Stormwater program and provides stormwater outreach materials.

Stormwater Discharges from Construction Activities. Provides general information and guidance for construction activities.

Stormwater Discharges from Industrial Facilities. Provides general information and guidance for industrial facilities.

Stormwater Discharges from Municipal Separate Storm Sewer Systems (MS4s) Program. Includes permit requirements and guidance for MS4s.

Stormwater Best Management Practices Calculator. Provides easy access to more than 220 studies assessing the performance of over 275 best management practices (BMPs).

Managing Wet Weather with Green Infrastructure. Summarizes common Green Infrastructure approaches and key resources for research, funding and partnerships.

Bioassessment and Biocriteria. Hosts introductory, technical and guidance documents on the use of biological assessments and data.

Top of Page