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Fall 2001 Issue

Total Maximum Daily Loads (TMDL) Defined

State adopts standards to protect our waters

Erosion brings nutrients and sediment into Sucker Creek, which in turn transports them to Little Rock Lake in Benton County.

The TMDL defines how much of a pollutant would be the maximum amount that could be discharged daily into a water resource from all sources in a surrounding area, while still allowing the water to be used for drinking water, fishing, swimming and other purposes.

For example, data from the Swan River, located in Todd and Morrison counties, indicated the presence of fecal coliform bacteria exceeding the TMDL standard. This type of bacteria is found in human and animal wastes and can signal the presence of infectious diseases including dysentery, salmonellosis and hepatitis. Simply stated, the water is unfit for human contact.

The MPCA, the two counties, Little Falls High School's River Watch Program and area citizens are conducting a TMDL study on the Swan River. Such a study is required by the Clean Water Act for each pollutant (in this case, fecal coliform) that causes a water resource to fail to meet the state's water quality standards.

During a TMDL study, both point and nonpoint sources are assessed. (A point source is a discharge from pipes or other discrete points. Nonpoint sources include diffuse sources such as erosion, atmospheric deposition and runoff.) Water-quality sampling and computer modeling determine how much each pollutant source must reduce its contribution to assure the water quality standard is met. Regulators then allocate how much each source must cut back on the pollutant to bring the water resource back in line.

The Swan River TMDL study is looking at all activities that could contribute to the high fecal coliform bacteria count. This includes wastewater treatment plant discharges (point sources), and feedlot runoff and individual septic treatment system failures (nonpoint sources). Land-use assessments and cost-share funding for best management practices are also considered.

More information about TMDLs is available on the MPCA's Web site.

- Kelli Huxford

(Contact the author at 218-828-6088 or by e-mail at kelli.huxford@pca.state.mn.us)