Under Section 303(d) of the Clean Water Act, all states, territories, and authorized tribes are required to develop a list of impaired waters.
These waters have been degraded or polluted to the point where they do not meet established standards and beneficial uses. These jurisdictions are required to develop Total Maximum Daily Loads (TMDLs) for these waters. A TMDL is a calculation of the maximum amount of pollutant that a water body can receive and still safely meet water quality standards. The most common TMDLs encountered are sediment, nutrients, metals, and temperature, although other site specific standards (ex: pathogens, pH, pesticides, etc.) may be required.
WET has been involved with TMDL development since the early 2000’s. Our environmental services staff has conducted many TMDL assessment studies on behalf of the Montana DEQ, watershed groups, conservation districts, and other interested stakeholders. Assessments have included pollutants of concern including sediment, nutrients, metals, and temperature, and typically include the following major tasks: watershed assessment and background GIS analysis, field assessment/sampling, data analysis/modeling, and development of 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 source (grazing, agriculture, urban) impacts;
• Streambank erosion studies from multiple land use impacts;
• Sediment delivery to waterbodies from unpaved road networks;
• Upland sediment delivery to waterbodies; and
• Temperature monitoring and modeling to determine impacts from multiple sources (irrigation, riparian corridor management, shade, etc.).
