Total Maximum Daily Loads

This page contains introductory information regarding total maximum daily loads (TMDLs). For more specific information, including regional issues and congressional activities, see the menu to the right.


Total Maximum Daily Load (TMDL) Program

New Hampshire Department of Environmental Services.

"The term 'total maximum daily load' (TMDL) refers to the calculation of the maximum amount of a pollutant that a waterbody can receive, and attain or maintain water quality standards for its designated use. The TMDL calculation allows for the determination of a carefully identified allowable pollutant load equivalent to the sum of the waste load allocations (WLA) for point sources, load allocations (LA) for nonpoint sources and naturally occurring background sources, and an allocation of that load among the pollutant's sources. The TMDL calculation is required to account for seasonal variations and it must include a margin of safety (MOS) that accounts for uncertainty and any lack of knowledge concerning the relationship between effluent limitations and water quality."

Waste lagoon TMDL Final Rule (PDF | 543 KB)

Environmental Protection Agency.

Provides the text of the Jul 13, 2000 Federal Register notice that contains the total maximum daily load final rule. See also the final rule fact sheet (PDF | 25 KB).

Impaired Waters and Total Maximum Daily Loads Program

Environmental Protection Agency.

Includes access to the documents, Approach for Using Load Duration Curves in the Development of TMDLs (PDF | 3.3MB) and Twenty Needs Report: How Research Can Improve the TMDL Program (PDF | 1.1MB). Also provides details about TMDL meetings and training courses, including Watersheds 103: TMDL Training for Practitioners, and links to EPA Regional TMDL (and other) Web sites.

Total Maximum Daily Load Research

USDA. National Agricultural Library.

Searches for TMDL-related citations in AGRICOLA, NAL's catalog of books and articles. Some full text materials are available.

Minnesota's Impaired Waters and TMDLs

Minnesota Pollution Control Agency.

"The federal Clean Water Act requires states to adopt water quality standards to protect lakes, streams, and wetlands from pollution. The standards define how much of a pollutant (bacteria, nutrients, turbidity, mercury, etc.) can be in the water and still meet designated uses, such as drinking water, fishing, and swimming. A water body is “impaired” if it fails to meet one or more water quality standards."

TMDLs and Agriculture in the West (PDF | 197 KB)

Environmental Protection Agency.

A brochure focusing on watershed-level approaches useful in the western United States. "A TMDL is the basis on which strategies to improve and protect water quality are developed. The agricultural community is being called on to use Best Management Practices (BMPs) in their operations to prevent water pollution."


New Mexico Environment Department.

Current state resources on TMDLs and related regulations. "A TMDL is defined as “a written plan and analysis established to ensure that a waterbody will attain and maintain water quality standard including consideration of existing pollutant loads and reasonably foreseeable increases in pollutant loads." (EPA 1999).

TMDLs: Frequently Asked Questions

Michigan Department of Environmental Quality.

A question-and-answer fact sheet. Each state identifies waterbodies within its boundaries which are not meeting Water Quality Standards and the reason why (for example, excess nutrients). To identify these lakes and streams in Michigan, we rely on water quality data that is less than five years old, and make sure the data is reliable.

Total Maximum Daily Loads (TMDLs)

Ohio State University Extension.

A fact sheet covering the definition of TMDLs and the procedures for development. "While pollution loads from point sources are generally known from NPDES (National Pollutant Discharge Elimination System) permits, pollution loads from nonpoint sources and background sources must be estimated. Because these sources are difficult to identify precisely, TMDLs will focus on estimating total, or aggregate, loads from nonpoint and background sources for the waterbody under consideration."