What is a TMDL?

When the amount of chemical, physical or biological agents in the water violate standards, DEQ prepares a water quality restoration plan that describes the severity of the problem and what needs to be done. The difference between the water quality standard for a pollutant and the actual amount present in the water is the reduction target. The reduction target is often referred to as a TMDL. Several activities may contribute to poor water quality, so the plan will suggest alternatives to reduce pollution from each one.

The goal of a water quality restoration plan is to reduce pollution by a specified amount (TMDL) so that the water can be put to full beneficial use by agriculture, communities, households, recreationists and wildlife. Cooperation is the best way to find an effective, fair and economical way to reduce pollution. The legislature wanted people to take part in water quality restoration voluntarily--especially the people whose activities are causing the water quality problem. The best solution is one that restores water quality and benefits or modernizes an operation. It’s the best because it is most likely to be properly installed and maintained.

A Water Quality Restoration Plan is a technical and legal document that includes:

• A list of applicable water quality standards
• An assessment of the sources of pollutants
• A description of the impaired streams or lakes
• A target measurement for each pollutant (usually the water quality standard)
• Pollutant reduction targets (TMDLs)
• A margin of safety that accounts for the uncertainty in the data, and an analysis of seasonal variation and future development impacts
• A monitoring plan to determine when reduction targets are met.
• Public participation and documentation