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Water: Water Quality Standards Academy

Basic Course: Supplemental Topics: The 303(d) List: Prioritizing Impaired/Threatened Waters

Listing Impaired Waters and Developing TMDLs

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After compiling the list of impaired/threatened water bodies, States/Tribes determine the priority ranking of waters for TMDL development. Under Section 303(d)(1) prioritizing the list must take into account the following for each water body (or segment):

  • Severity of the pollution.
  • Uses to be made of such waters.

States and tribes may consider other factors such as:

  • Risk to human health and aquatic life.
  • Degree of public interest and support.
  • Recreational, economic, and aesthetic importance.
  • Vulnerability or fragility as an aquatic habitat.
  • Immediate programmatic needs (e.g., wasteload allocations needed for permits coming up for revision or for new or expanding discharges).
  • Court orders and decisions relating to water quality.
  • National policies and priorities.
Resource. For more on considerations involved in prioritizing, see EPA's Guidance for Water Quality-Based Decisions, Chapter 2.

States/Tribes must develop a priority-ranked list of impaired or threatened waters. The regulation recognizes that not all water quality problems can be addressed at once. Nonetheless, the expectation is that over time a State/Tribe will develop and implement TMDLs for all impaired/threatened waters identified within its boundaries. Thus, each State/Tribe must establish multi-year schedules that address near-term development of TMDLs for high-priority waters as well as eventual TMDL development for other waters on the list.

Key Point. EPA recommends that rankings be either in the form of a scheduled TMDL completion date or a ranking such as high, medium, or low. With this type of approach, the most severe water quality problems or most toxic pollutants need not always be given the highest priority for TMDL development if circumstances warrant a lower priority (e.g., source identification analysis needs to be completed before TMDL is developed).
Key Point. The regulations require the State/Tribe to determine schedules for the development of TMDLs (40 CFR 130.7(d)(1)). EPA recommends, however, that the TMDLs be developed as expeditiously as practicable.
Key Point. The TMDL development schedule must identify high-priority waters that will be "targeted for TMDL development in the next two years" (40 CFR 130.7(b)(4)). While there is no time frame established by statute or the regulations for completion of TMDL development, EPA guidance recommends an 8-to-13 year time frame that runs from the water's initial listing as impaired or threatened.
Key Point. EPA has 30 days to approve or disapprove the state/tribe's 303(d) list submission. If EPA disapproves the list, the Agency has 30 days to establish the state/tribe's list.

For informational purposes only–Not official statements of EPA policy.

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