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Although the acronym has been in place for several decades, Manitowoc County soil and water department director Jerry Halverson described it as 'a new concept' in an update report at the county forage council's summer field day.

Halverson was referring to TMDL, which stands for the total maximum daily loading of phosphorus and sediment runoff that is acceptable for avoiding a state of Wisconsin Department of Natural Resources designation of a river, stream or lake as an 'impaired body of water' because of low water quality. There are nearly 1,300 of those designations within the state.

What's new is that TMDL is set to be applied more extensively, particularly in the Manitowoc River basin which includes most of Manitowoc County and parts of Calumet, Fond du Lac, Brown and Kewaunee counties, Halverson explained.

In the past, only the identified 'point sources' of discharges to bodies of water faced mandatory limits, Halverson observed. What's new is that 'non-point sources' will also be targeted in the future rather than merely being encouraged to carry out voluntary practices.

Historical review

The concept of TMDL is based in the federal Clean Water Act of 1972, Halverson said. Starting in the late 1970s, it led to the development and funding for vegetative areas, grass waterways and barriers around livestock facilities to reduce runoff of contaminants to bodies of water.

Both point (constructed sites) and non-point (agricultural and other open land) sources are now being checked for their contributions to TMDL, Halverson noted. Urban stormwater runoff is also subject to the TMDL guidelines.

Satellite imagery is being used to identify new probable problem sites, Halverson said. He predicted that this research and the related creation of models would take three to four years and would require adequate funding in order to enforce compliance.

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