Total Maximum Daily Load (TMDL)

General Information: A Total Maximum Daily Load (TMDL) is the maximum amount of a single pollutant that can enter a waterbody, from both point and nonpoint sources, with that waterbody still meeting water quality standards set by the state. Water quality standards are based on the intended use, such as drinking water, aquatic life habitat, or recreational usage. In establishing a TMDL, a margin of safety must be included according to that intended use for the waterbody. A TMDL must allow for seasonal variations in the waterbody as well (EPA, 2001a).

The TMDL program and water quality standards were established in the 1972 Clean Water Act, section 303, but only recently have they begun to be implemented. The EPA issued regulations in 1985, amended in 1992 (40 CFR part 130, section 130.7), to implement TMDL programs. New recommendations were designed in 1999 (EPA, 2001a).

States are required to submit a list to the EPA of waterbodies not meeting local water quality standards and prepare TMDLs for those waterbodies. The EPA then accepts or rejects the list. If rejected, the EPA is responsible for developing the list (EPA, 2001a).

For up-to-date information, visit the EPA's TMDL Program.

Other TMDL Links:

• Capitolink
• National Forest Service
• National Wildlife Federation - Factsheet on TMDLs
• New Mexico Environment Department, Surface Water Quality Bureau
• State of Michigan, Department of Environmental Quality
• National Corn Growers Association, Conservation and the Environment, TMDL

NCSU Water Quality Group

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