Total Maximum Daily Loads (TMDL)


In Idaho, State Water Quality Standards have been established and approved by the U.S. Environmental Protection Agency (EPA). These standards, required under the Clean Water Act, are designed to protect, restore and preserve water quality in areas designated for specific uses including drinking water, swimming, recreation, fishing, cold water fisheries (e.g. salmon and trout habitat), etc. Appropriate "designated uses" have been identified for each water body within Idaho.

When a lake, river or stream fails to meet the water quality standards that support its designated use, specific actions are required under State and Federal law to ensure that the "impaired" water body is restored to a healthy fishable, swimmable condition. Almost 1,000 sections of rivers, streams and lakes have been identified as impaired in the State of Idaho.

The State of Idaho and the EPA have a legal, court-ordered responsibility to ensure that these impaired waters be dealt with in a timely manner. In technical terms, this means that a "TMDL" must be developed for each impaired water body.

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What is a TMDL?

A TMDL (Total Maximum Daily Load) is a written, quantitative assessment of water quality problems and contributing pollutant sources. It specifies the amount of pollution reduction necessary to meet water quality standards, allocates the necessary pollutant limits among the various sources in the watershed and provides a basis for taking actions needed to restore a waterbody. TMDLs range from ten to over 100 pages in length, depending on the complexity of the issues. The goal of a TMDL is to attain state water quality standards.

A TMDL is a technical and legal document which must include:

The EPA has the responsibility to approve or disapprove TMDLs.

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What types of pollutants are at issue?

Pollutants of concern vary from watershed to watershed. In much of rural Idaho, water quality concerns center around excess sedimentation, elevated temperatures and nutrient overloading. In developed areas, concerns may focus on fecal coliform, oil and grease or dissolved oxygen. In industrial areas, heavy metals such as lead, zinc and copper or organic chemicals such as benzene, napthelene or chloroform may be at the top of the list.

In general, watersheds are subject to two broad categories of pollution: Point Source and Non-point Source. Point Source Pollution is typically associated with industrial discharges, municipal waste treatment facilities and animal feedlots. The effects can be directly traced to a particular source or facility. Point source pollution can often be measured at an outfall or pipe. Non-point Pollution, on the other hand, is more difficult to identify. It includes, among other things, the cumulative effects of fertilizers and pesticides that farmers and homeowners may use, oil that is carelessly poured down storm drains, and land use practices of urban development, agriculture and forestry.

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Who is responsible for Watershed Management?

The short answer is anyone living within the watershed. Watersheds include the surrounding land, the rivers and the streams that eventually drain into lakes, underground aquifers and ultimately the ocean. Many human activities (farming, forestry, and urban development among them) have the potential to adversely affect the quality of our water. Recovery plans for impaired waters require the participation of the key players in any given watershed.

Who writes the TMDL?

TMDLs are written by technical experts in water quality and related fields. Watershed Advisory Groups (WAGs) provide information, advice and local knowledge for the decision makers. Typically, Idaho Division of Environmental Quality (IDEQ) does the bulk of the writing. On reservations EPA is likely to take the lead with considerable help from the State, the Tribes and other agencies. When a particular member of the TAG has expertise in a given area, they are likely to play a key role in writing the portion of the TMDL that applies to their expertise.

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What happens after the TMDL is complete?

When the TMDL is completed, the task is to implement its recommendations and meet its goals. State and Federal government can often assist in this process by providing technical assistance and grants, but it is the residents of the watershed, the businesses and the land owners who will determine success. The Watershed Advisory Groups are in a key position to lead the implementation plan. And, of course, it is not the plan, but the results of that plan that will return our waters to a healthy state for both humans and aquatic species that will support swimming, recreation and fishing. Clearly, communities need to be involved in solving the problems, and clearly communities will benefit from the end results.

Whom do I contact for more information?

The Idaho Department of Environmental Quality has more TMDL information, and contacts and links to statewide implementation plans, or contact the US Environmental Protection Agency, (208) 378-5746. The EPA has a national index page for TMDLs and extensive additional information for the Pacific Northwest (Region 10).

The Idaho DEQ has more background information on TMDLs on its website, with links to reports and implementation plans.

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