What is a TMDL?
Total Maximum Daily Load refers to the maximum amount of a pollutant a water can receive and meet water quality standards.
A TMDL can also be defined as a reduction in pollutant loading that results in meeting water quality standards.
A TMDL document is developed that provides a framework water quality improvement plan for streams that have been determined not to meet water quality standards. In Montana, documents are developed for geographical areas called TMDL Planning Areas (TPAs). You will see some of those TPAs in the sidebar to the right.
The TMDL document will contain information that:
- Characterizes the stream
- Defines the extent of the water quality problem
- Determines the sources of the problem and how much each source is contributing
- Identifies the acceptable load of the pollutant that the stream can receive (the TMDL)
- Determines the amount of reduction needed from each source to satisfy the TMDL
- Most documents will also contain strategies and recommendations for reducing the amount of the pollutant entering the stream.
Schematic of TMDL Concept:
This schematic demonstrates both nonpoint (Sources X, Y, & Z) and point (Pt Sources A & B) source contributions as part of the Existing Load in the stream, in addition to the natural (also referred to as background) load. A reduction is needed in the existing load in order to meet Montana Water Quality Standards and also the determined TMDL.
For additional information on nonpoint source pollution, see DEQ's Nonpoint Source Web Page and Wiki.
Downloadable TMDL Pamphlet:
Understanding the TMDL Process (PDF 0.5MB)
Hard copies are also available. Please contact Christina Staten to obtain copies.
For Additional Information Please See the DEQ TMDL Web Page
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