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Total Maximum Daily Loads (TMDLs)
TOTAL MAXIMUM DAILY LOADS (TMDLs)
When a lake or stream does not meet Water Quality Standards (WQS), a study must be completed to determine the amount of a pollutant that can be put in a waterbody from point sources and nonpoint sources and still meet WQS, including a margin of safety. A TMDL is used as a short hand acronym to describe the process used to determine how much pollutant load a lake or stream can assimilate.
Frequently Asked Questions
What are Water Quality Standards?
Water Quality Standards are state rules established to protect the Great Lakes, the connecting waters, and all other surface waters of the state. These rules define the water quality goals for a lake or stream. The goals are in three areas:
1. Uses of the lake or stream, such as swimming and fishing;
2. Safe levels to protect the uses, such as the minimum oxygen level needed for fish to live;
3. Procedures to protect high quality waters.
Why are TMDLs being developed?
TMDLs are required by the federal Clean Water Act for waterbodies that do not meet WQS. TMDLs are receiving more attention now because of the several recent lawsuits in federal courts.
How is it decided which waterbodies need TMDLs?
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.
Who is responsible for developing TMDLs in Michigan?
The Michigan Department of Environmental Quality is responsible for developing TMDLs.
How is a TMDL developed?
A TMDL is developed by determining the maximum daily load of a pollutant that a waterbody can assimilate and meet Water Quality Standards. This load is then allocated to point source discharges, nonpoint source discharges, and a margin of safety reserve (to account for technical uncertainties).
What is the role of Local Communities and Landowners in the development of TMDLs?
TMDL development is a public process that works best with the involvement of all affected parties. This is particularly important during the discussion on allocation and implementation issues. Participation by local communities and landowners leads to more representative TMDLs that can be readily implemented. This leads to quicker improvements in water quality.
What happens once a TMDL is developed?
Following development of a draft, a TMDL is noticed for public comment. After making any appropriate modifications in response to the public comment, the TMDL is sent to the United States Environmental Protection Agency for approval. Once approved, the state is required to implement the TMDL so the waterbody will meet Water Quality Standards. The TMDL is implemented through existing programs, such as NPDES permits for point source discharges and nonpoint source control programs, to achieve the necessary pollutant reductions.
What TMDLs have been developed and
Links to individual TMDLs are located within the Approved TMDL List.