Spokane River snippet

Spokane dissolved oxygen TMDL

What does the TMDL do?

Total Maximum Daily Loads (TMDLs), also known as water quality improvement projects, are required by the Clean Water Act (CWA) to return water bodies on the Water Quality Assessment (303[d]) list to a healthy condition. TMDLs established today can also help manage water quality on a watershed scale to prevent the loss of beneficial uses in the future.

A TMDL includes:

  • An assessment of the water quality problems.
  • A technical analysis to determine how much pollution must be reduced from all sources to meet water quality standards.
  • The selection and implementation of appropriate control measures.
  • Follow-up monitoring to determine the success of the effort.

TMDLs are established for each water quality problem to protect all designated “beneficial uses” of the river, which include swimming, boating, fishing, providing aquatic habitat, providing aesthetic value and supplying drinking, irrigation, and industrial water.

TMDLs have been established in the Spokane River for metals (lead, cadmium, and zinc) and for phosphorus (a nutrient that feeds plants) to control excessive algae blooms in Lake Spokane. The 2010  Spokane Dissolved Oxygen TMDL replaces the total phosphorus TMDL developed in the late 1980s.

What the 2010 Dissolved Oxygen TMDL requires

The 2010 Spokane River Dissolved Oxygen TMDL requires the following improvements over a ten year time period:

  • Removal of >90 percent of total phosphorus in NDPES wastewater treatment plants (point sources) in Washington.
  • Reduction in nonpoint sources of phosphorus (Hangman Creek and Little Spokane River) of up to 50 percent based on a low flow year (2001).
  • Improvement of dissolved oxygen (DO) conditions in Lake Spokane by Avista Utilities.

For NPDES permit holders, they will meet their obligations primarily through enhanced treatment technologies. Agricultural nonpoint sources will be reduced through government cost-share programs working with farmers and conservation districts. Nonpoint source reductions are also expected in the city of Spokane stormwater discharges (in part due to recently issued municipal stormwater NPDES permits) and from septic tank removals in Spokane Valley. Avista will meet its DO obligations through numerous actions identified in a DO Water Quality Attainment Plan.

To meet these ambitious targets, stakeholders on the Spokane River have had regular meetings as an advisory committee since 2011 to discuss progress and develop tools to meet these three primary goals. NPDES permit holders are exploring other methods, such as extending treatment season windows, to meet their goals in addition to treatment technologies. Local conservation districts and other organizations are continuing to pursue nonpoint source reduction projects through government cost-share programs. A system to track nonpoint source reductions throughout the 6,000 square mile watershed is being pursued by Ecology and other groups.

By 2021, a ten-year assessment will be developed to determine the success in meeting these goals through numerous measures. While it is early in the process, such measures will likely include but not be limited to: meeting water quality standards throughout the river, showing improvements in aquatic habitat, evaluating the performance of advanced wastewater treatment facilities, and the effort and water quality impacts of reducing the nonpoint sources described above.

See “Implementation Schedule and Actions” for more information on specific activities to implement the TMDL.

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Last updated December 2012