What is a TMDL?

A TMDL - or total maximum daily load &endash; is a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards. In other words, it is the sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources, and includes a margin of safety and consideration of seasonal variations. In addition, a TMDL contains the reductions needed to meet water quality standards and allocates those reductions among the sources in the watershed.

Who is responsible for establishing and implementing TMDLs?

States are responsible. If they fail to establish the TMDLs, EPA must do it. In the State of Wisconsin it is the Department of Natural Resources that is responsible for TMDLs.

How are TMDLs implemented?

TMDLs may be implemented in many ways: through state nonpoint source management programs; other federal laws and requirements, e.g., the Farm Bill, state and local laws and ordinances; as well as local or regional watershed management programs. The proposed regulations would require that some "reasonable assurance" of implementation be included in the TMDL. The EPA as well as the state have the discretion to designate certain dischargers causing significant water quality impairment as point sources requiring an discharge permit. Dischargers that may be designated include selected animal feeding operations, aquatic animal production facilities, and silvicultural operations.

When do TMDLs need to be established?

TMDLs should be established over a 15 year timeframe with water bodies determined to be higher priority waters established earlier in this timeframe. Priorities are based on the severity of the pollution and uses of the water body. The proposed changes would require that some impaired waters that are drinking water sources or have endangered species also be given priority.

What are the major causes of impairments in our water bodies?

Both the 1996 and 1998 section 303(d) impaired water lists, as well as the section 305(b) report, reflect similar patterns with sediments, nutrients, and pathogens being the top three causes of impairment. Other causes include: dissolved oxygen, habitat and flow alterations, pH, metals, mercury (including fish advisories), and pesticides. Tainter Lake, Lake Menomin and a portion of the Red Cedar River are on the state impaired waters list because of water quality problems due to high levels of phosphorus.

What is the relationship of TMDLs to the watershed approach?

Lasting solutions to water quality problems are best achieved by looking at all activities in a watershed. TMDLs are an important part of translating water quality standards into any point and nonpoint source load reductions needed to achieve healthy watersheds. EPA encourages watershed approaches in establishing TMDLs so that the cumulative and synergistic effects may be considered. TMDLs will be less expensive and more effective when bundled together to clean up an entire watershed. At the watershed level, TMDLs can structure innovative solutions, e.g., nutrient trading among wastewater dischargers and nonpoint sources; or the development of new point or nonpoint source technologies. The watershed action strategies developed in response to the Clean Water Action Plan are also a vital tool in meeting our clean water goals.