Impaired Waters Support

Under Section 303(d) of the Clean Water Act, all states, territories, and authorized tribes are required to develop a list of impaired waters.

Impaired waters have been degraded or polluted to the point where they do not meet established standards and beneficial uses. States are required to develop Total Maximum Daily Load (TMDL) for these waters, which is a calculation of the maximum amount of pollutant that a water body can receive and safely meet water quality standards and beneficial uses. The most common TMDLs are developed for sediment, nutrients, metals, and temperature, although other site-specific standards also exist.

WET has been involved with TMDL development since the early 2000’s and our environmental services staff has conducted TMDL assessment studies on behalf of Montana Department of Environmental Quality (MDEQ), numerous watershed groups, multiple conservation districts, and many other stakeholders. Past projects have included watershed-scale assessments for water quality sampling and stream habitat and major tasks of these assessments include background GIS analysis, field assessment and sampling, data management and analysis, and modeling pollutant reduction scenarios using selected Best Management Practices (BMPs).

Specific stream impacts that WET personnel have studied in detail include:

  • Heavy metals impacts from past mining activities
  • Nutrient impacts from point (wastewater discharge) and non-point sources (grazing, agriculture, or urban)
  • Streambank erosion studies from multiple land use impacts
  • Sediment delivery to waterbodies from unpaved road networks
  • Upland sediment delivery to waterbodies
  • Temperature monitoring and modeling to determine impacts from multiple sources (irrigation, riparian corridor management, shade, etc.)


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