Welcome to the Montana Department of Environmental Quality's
Total Maximum Daily Load (TMDL) Home Page.

DEQ Environmental Specialist examining bug collection from river.

DEQ is required to develop Total Maximum Daily Loads (TMDL) for all water bodies on the 303(d) list. A TMDL is the total amount of a pollutant that a water body may receive from all sources without exceeding water quality standards. A TMDL can also be defined as a reduction in pollutant loading that results in meeting water quality standards.  Montana’s approach is to include TMDL as one component of a comprehensive water quality restoration plan.

Developing a TMDL water quality restoration plan is often a challenge. There are many legal, technical, social, economic and natural variables to consider. It is not always easy to link a particular cause of impairment to a specific source. Rivers, lakes and streams change from one season to the next; one year to another.  The plan must account for seasonal variations in flow and include a margin of safety. The margin of safety addresses uncertainties about the link between pollutant loads and impairments. Many TMDL plans rely on adaptive management to fine tune the targets and load allocations in response to monitoring data.

The Department of Environmental Quality is using a watershed approach to facilitate development of water quality restoration plans. DEQ has divided the state into 91 watershed planning areas and adopted a schedule for completing TMDL restoration plans for all areas by December 2012.