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Statewide Mercury Total Maximum Daily Load (TMDL)

The U.S. Environmental Protection Agency approved Minnesota's Statewide Mercury Total Maximum Daily Load study in March 2007. Since then, the MPCA has worked with stakeholders representing a broad range of interests to identify strategies and timelines that would be included in an implementation plan. The stakeholders' recommendations, completed in June 2008, are contained in the Strategy Framework for Implementing Minnesota's Statewide Mercury TMDL .

The impaired waters TMDL process consists of data collection and assessment, listing those waters not meeting water quality standards, developing a pollution reduction plan, implementing the plan, and then evaluating the implementation by collecting more data.

The Statewide Mercury TMDL

There is a strong connection between the Minnesota Department of Health Fish Consumption Advisory (FCA) and MPCA’s impairment determination. When the FCA limitation is more restrictive than one meal per week, the water body is impaired.

There are strong regional differences between northeastern (NE) Minnesota, dominated by forests and wetlands, and the rest of the state, with the NE having significantly higher mercury concentrations in fish.

Atmospheric deposition of mercury is uniform across the state and supplies more than 99.5% of the mercury getting into fish. Agency research has demonstrated that 70% of current mercury deposition in Minnesota comes from anthropogenic [people] sources and 30% from natural sources, such as volcanoes. There are no known natural sources in the state that emit mercury directly to the atmosphere.

There is a slight general downward trend in fish tissue mercury concentrations, but lakes still remain impaired. About 90% of the mercury deposition in the state originates from outside the state, so the first cut allocation is a 90% federal share and a 10% state share; the federal government will be responsible for meeting its reduction goal, developing schedules and meeting reasonable assurance requirements of the Clean Water Act (CWA).

The long-term goal of the mercury TMDL is for the fish to meet water quality standards; the approach for Minnesota’s share is mass reductions from state mercury sources. This mercury TMDL establishes that there needs to be a 93% reduction in state emissions from 1990 for the state to meet its share. Water point sources will be required to stay below 1 percent of the total load to the state and all but the smallest dischargers will be required to develop mercury minimization plans. Air sources of mercury will have a 93% emission reduction goal from 1990 levels. Air sources will be divided into three sectors: products, energy, and mining.

By the numbers

The 2014 Revision to the TMDL included:

  • 43 new waterbodies added Appendix A, the list of lakes and stream segments included in the TMDL
    • 14 stream segments
    • 29 lake basins
  • An updated Appendix B, the list of 935 water point sources which contribute mercury to the waterbodies identified in Appendix A

The Statewide Mercury TMDL now contains:

  • 1272 total impairments for mercury
    • 1250 for mercury in fish tissue
    • 22 for mercury in the water column
  • 880 lake basin impairments
  • 392 stream segment impairments
  • Impairments close to evenly split between the southwest and northeast parts of the state

Revisions to the TMDL

Every two years, the MPCA updates information in the approved statewide mercury TMDL. Mercury impairments in the state are mainly for fish tissue concentration exceedences but can also be for water column mercury concentration exceedences. These impairments are listed in Appendix A of the Impaired Waters List. Fish tissue impairments in the List have mercury concentrations greater than 0.2 mg/kg and equal to or less than 0.572 mg/kg. Greater concentrations are not assigned to the mercury TMDL and result in inclusion in the TMDL List. It is important to note that the mercury TMDL documentation and reduction goals are NOT being changed with Appendix A revisions. The last revision was to the 2014 Appendix A and was approved by EPA on September 24, 2014. To see the 2014 draft Impaired Waters List and draft Appendix A, please visit the Impaired Waters List webpage.

Contact Information

Miranda Nichols
Minnesota Pollution Control Agency
520 Lafayette Road N
St. Paul, MN 5515-4194
651-757-2614; 800-657-3864

Last modified on September 11, 2015 09:57