The development of Total Maximum Daily Loads (TMDLs) has increased markedly in recent years and as of spring 2014, over 70,000 TMDLs have now been completed. For much of the TMDL Program's history, it has been difficult to analyze the program's environmental results because the entire sequence of TMDL development, TMDL implementation and impaired waters recovery often takes several years.

TMDLs are producing results that provide an opportunity to assess how well the TMDL Program is working. Results analysis involves assessing measures of environmental outcomes, their probable causes, and program progress in order to generate the insights needed to improve impaired waters programs. In 2010 a TMDL Program Analysis Project was undertaken to improve our understanding of TMDL-specific program results patterns, explain these patterns and develop appropriate technical, programmatic and policy actions to incorporate these findings at state, regional and national program levels.

The Clean Water Act's impaired waters program process (above) is a simplified graphical representation of how impaired waters are restored. The programmatic stages of this process are listed below:

• listing;
• planning;
• implementing;
• improving and
• recovery.

Although the primary role of EPA’s TMDL Program is limited by statute to the first two stages of the process, delegated state, tribal and territorial TMDL programs carry on the latter three stages with EPA assistance. The analysis project has intentionally focused on program results at all five stages to learn about progress and the effects of EPA’s programs at each stage.

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