About TMDLs

Impaired Waters
Federal standards exist for basic water pollutants such as sediment, bacteria, nutrients and mercury. A water body is considered "impaired" by the Environmental Protection Agency (EPA) if it fails to meet one or more of these water quality standards. The federal Clean Water Act (CWA) requires the Minnesota Pollution Control Agency (MPCA) to identify and restore impaired waters in our state.

Minnesota's impaired waters list identifies waters that do not meet water quality standards. Once a water body is placed on the list, the CWA requires the completion of a TMDL study.

Total Maximum Daily Loads (TMDLs) - The Process
The term TMDL isn't as intimidating as people think. It's basically just a formula or mathematical equation. The process involves a technical study with extensive stakeholder and public input as well as intensive water monitoring. The process is typically:

1. Assess water quality
2. List water bodies that do not meet standards as impaired
3. Create a TMDL Report to identify sources and reductions needed
4. Develop Implementation Plan to identify best management practices and begin restoration activities
5. Re-evaluate water quality

TMDLs - The Number
A TMDL number is a calculation of the maximum amount of a pollutant a water body can receive and still meet water quality standards. It involves runoff calculations as well as waste water load allocations for sanitary treatment centers and can involve many other factors. The TMDL is a measurement based on the rivers capability to handle whatever the nutrient and still maintain recreational suitability for swimming, fishing, and other community water uses. If a TMDL for sediment is 75 tons per day, that means that water samples being taken throughout the river cannot exceed that limit or it will be impaired. These limits typically are reinforced by state or federal statute.

Developing a TMDL Report & Implementation Plan
The TMDL process results in a pollution reduction plan. The plan identifies all the sources of pollutants in the watershed, either natural or human-caused, and allocates needed reductions among them. Seasonal variability in water conditions is taken into account when calculating the TMDL.

Once a TMDL is completed and approved by the EPA, a detailed implementation plan is completed which identifies practical management measures needed for the water body to meet the water quality standards.

Please see the Projects section for more specific information about the Fecal Coliform and Turbidity TMDLs in the Pomme de Terre Watershed.