Aitkin Agri-Peat Mercury Pollution

Minnesota Peat Mining

Peatlands are one of Minnesota’s most extensive ecosystems, covering over seven million acres – more than 10 percent of the state. These peatlands have been about 6,000 years in the making, and many are located in northern Minnesota. Peat functions as a natural water filter and prevents flooding. Peat bogs sequester carbon, mitigating climate change. Peat bogs also sequester mercury deposited from air emissions. When peat is excavated, this mercury can be released to nearby waters, becoming a source of methylmercury that contaminates fish.

As of January 2020, the Minnesota Department of Natural Resources (DNR) reported nine active peat mining leases with 8,176 acres of active peat mine leases.

Peat mining in Minnesota. The Regulatory Review photo.

Aitkin Agri-Peat Mercury Limits

The Aitkin Agri-Peat mine in Cromwell, Minnesota, requested a permit from the U. S. Army Corps of Engineers to reopen hundreds of acres of bogs and wetlands for peat mining in the Mississippi River Watershed. In connection with the re-opening of the Agri-Peat Cromwell mine on June 7, 2011, the Minnesota Pollution Control Agency (MPCA) gave notice of its intent to issue a National Pollutant Discharge Elimination System/State Disposal System (NPDES/SDS) water pollution permit for the peat mine.

The proposed permit would have allowed re-opening of a peat mine without setting any limits for mercury discharge. WaterLegacy’s research disclosed the following:

  • The prior permit for the Aitkin Agri-Peat mine had contained a water quality based effluent limit (WQBEL) for mercury.
  • The Aitkin Agri-Peat mine had a history of violating mercury standards.
  • The waters into which the Aitkin Agri-Peat mine discharges are waters already impaired for mercury, so that fish already have excessive mercury contamination.
  • The federal Clean Water Act prohibits “backsliding,” namely weakening of water quality permits, such as removing a mercury limit from a permit like the Aitkin Agri-Peat permit.
WaterLegacy submitted comments and exhibits requesting mercury limits and worked with U. S. Environmental Protection Agency (EPA) staff to advocate for limits on Aitkin Agri-Peat mercury discharge.

Success in limiting mercury: As a result of WaterLegacy’s advocacy and the work of EPA permit program staff, MPCA conducted an analysis and determined that Aitkin Agri-Peat mining had the reasonable potential to cause exceedances of mercury in surrounding waters.

When the Aitkin Agri-Peat water pollution permit was issued in 2013, it contained water quality-based limits on mercury. As a result, the peat mine was redesigned with sedimentation basins to reduce mercury discharge.

Impact on Mercury Limits for Other Permits

American Peat Technology

When the American Peat Technology peat mine water pollution permit was proposed by MPCA in 2016, MPCA performed an analysis and determined that American Peat had the reasonable potential to cause exceedances of mercury standards. The MPCA required mercury limits, and WaterLegacy’s advocacy was limited to requesting more frequent monitoring and averaging to determine compliance.

PolyMet NorthMet Copper-Nickel Mine

When the MPCA proposed the draft water pollution permit for the PolyMet NorthMet copper-nickel mine in 2018, WaterLegacy and tribal allies raised concerns about mercury that would be released when mine site wetlands and peatlands were excavated. MPCA did not perform a reasonable potential analysis to determine if mercury limits were needed or if additional methods were needed to mitigate mercury discharge at the mine site.

Based on EPA staff experience beginning with the Aitkin-Agri Peat water pollution permit, EPA program staff comments on the draft PolyMet permit highlighted this deficiency:

[T]he stormwater general permit would authorize discharge from the draining of over 900 acres of wetlands, which are dominated by peat bogs. This activity is expected to release significant amounts of mercury into downstream navigable waters. While MPCA has acknowledged and addressed such discharges in its peat mining permits (and in verbal comments regarding this project), nothing in the permitting record demonstrates that this issue has been addressed or even considered. There is no provision in the construction stormwater general permit for addressing specific water quality standards issues. Thus, the draft permit (and associated permitting scheme) appears to leave mercury from this aspect of the project wholly unregulated. We suggest identifying what is intended to be covered under the stormwater general permit and evaluate whether there is reasonable potential for discharges from activities covered under the stormwater general permit to cause or contribute to excursions from water quality standards. If there is such reasonable potential, coverage under the stormwater general permit would not be appropriate. Rather this discharge, with appropriate WQBELs [water quality-based effluent limitations], could be covered under the NorthMet permit or another individual permit.
One of the issues currently in litigation is whether MPCA’s failure to require water quality-based effluent limits for mercury in the PolyMet NorthMet water pollution permit violated the federal Clean Water Act.