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TMDL overview
Overview of TMDLs.
TMDL development
TMDLs in development.
TMDL approvals
List of TMDLs approved by USEPA.
TMDL implementation
TMDL implementation.
Wastewater, Storm Water, CAFOs
Point source issues in TMDLs.
Nonpoint source
Runoff and stormwater related to TMDLs.
TMDL map and projects
Map of TMDL Projects and New Project Pages.
Contact information
For information on tmdls, contact:
Kevin Kirsch
Water Quality Bureau

What is a Total Maximum Daily Load (TMDL)?

Waldo Tributary

Waldo Tributary.

Impaired waters in Wisconsin are addressed through an analysis, known as a Total Maximum Daily Load (TMDL). A TMDL is the amount of a pollutant a waterbody can receive and still meet water quality standards. Basically it is a pollution "budget" for a water body or watershed that establishes the pollutant reduction needed from each pollutant source to meet water quality goals.

Section 303(d) of the Clean Water Act requires all states to develop TMDLs for waters on the Impaired Waters List. A TMDL is the amount of a pollutant a water can receive and still meet water quality standards. The analysis can be expressed as a formula:

TMDL = Wasteload Allocation (WLA) + Load Allocation (LA) + Margin of Safety (MOS).

The WLA is the total allowable pollutant load from point sources (municipal and industrial wastewater facilities, CAFOs, and MS4s). The LA is the load assigned to nonpoint sources (agricultural runoff, non–regulated urban areas). The MOS is the margin of safety which accounts for any uncertainty in the analysis and modeling.

To establish a TMDL, Wisconsin’s numeric water quality standards or applicable water quality targets based on narrative water quality standards are used. Water quality monitoring and measured flow in the watershed quantify current pollutant loads to the impaired water. To calculate the pollutant loads, computer models are used. Specific information for the model is needed such as: weather, topography, soil types, and land use. With these and other data inputs, the model simulates physical processes associated with the flow of water, sediment movement, nutrient cycling, crop growth, etc. Models can also be used to predict impacts of changes in land use, climate, and management practices on water quality. TMDL modeling determines the existing load and the target load to calculate the load reduction needed from each pollutant source.

Public input is very important during the development of TMDLs. All TMDLs require a minimum 30–day public comment period and public informational meeting or hearing. Once comments are addressed, the TMDL is approved by the State of Wisconsin and the US Environmental Protection Agency. Once approved, TMDLs are automatically amended to the Areawide Water Quality Mangement Plan. TMDL Implementation occurs through other programs such as the WPDES program and NPS program.

Last revised: Wednesday December 04 2019