MPCA invites public to discuss Met Council’s plan to expand state’s largest wastewater treatment plant

The Met Council is planning to expand the wastewater treatment plant near Pigs Eye Lake, and the Minnesota Pollution Control Agency released data for the public to review on that project.

The MPCA released an environmental assessment worksheet (EAW), a draft of an air emissions permit and a State Implementation Plan (SIP) for a new proposed sewage sludge incinerator at the Met Council’s Metro Wastewater Treatment Plant near Pigs Eye Lake in St. Paul.

Those documents can be found by visiting the MPCA’s public comments website.

The public is invited to review these materials and speak during the public comment period on Aug. 14 from 5:30 – 7:30 p.m. at Dayton’s Bluff Recreation Center in St. Paul.

The wastewater treatment plant is the largest in the state, with more than 180 million gallons of wastewater and 850 tons of solid waste handled by the plant daily with its three incinerators.

The Met Council plans to add a fourth incinerator to accommodate the nearly 25% more wastewater created by the growing Twin Cities population. Adding another incinerator means the facility needs an amended air emissions permit and a site-specific State Implementation Plan to meet requirements from the U.S. Environmental Protection Agency. This is because of the county’s historic pollution of coarse particulate matter (PM10), according to a news release from MPCA.

The three documents are meant to assess all significant environmental impacts in order to protect the environment and nearby residents from air pollution generated by the new incinerator, MPCA said.

The EAW reviewed possible impacts on air, local geology, soils, groundwater, surface water and other potential environmental impacts. The EAW made the following discoveries:

  • The expanded facility will use an additional 58 million gallons of groundwater annually, staying within the permitted limit of 1.5 billion gallons per year.
  • The project will add 1.3 acres of paved surfaces at the site, which leads to increased stormwater runoff. The Met Council will reconfigure existing stormwater basins to increase capacity to collect and treat the runoff.
  • Currently, per- and poly-fluoroalkyl substances (PFAS) are found in the incoming wastewater, but the processes at Metro Plant do not contribute PFAS to the recycled wastewater. The exact level of PFAS in the recycled wastewater and the resulting air emissions from the incineration process is currently unknown. Since the project will not handle more wastewater until the population grows, it is not expected that additional PFAS will be introduced into the recycled wastewater stream soon.

MPCA expects the new incinerator, which is similar in design and size to the other incinerators, to produce about 25% more emissions. The new air emissions permit will require the Met Council to install and maintain several controls in order to reduce emissions. Those controls include:

  • Carbon injection (for mercury and dioxins/furans).
  • A fabric filter baghouse (for particulate matter and heavy metals).
  • A venturi scrubber (for acid gases, particulate matter, heavy metals, and dioxins/furans).
  • A wet electrostatic precipitator (for particulate matter and heavy metals).

The MPCA said it is also making “minor changes” to the State Implementation Plan, including specific air modeling. In 1987, the concentration of PM10 in Ramsey County exceeded the federal limit. The EPA then intervened by requiring a State Implementation Plan which includes measures to improve air quality. This was met by a 20-year maintenance plan to meet those air quality requirements, and ambient air is now in compliance with EPA standards. MPCA said that even though the plan expired in Sept. 2022, existing equipment at the facility must continue to adhere to the SIP conditions.