State’s largest wastewater treatment plant to increase capacity by 25%
The Minnesota Pollution Control Agency (MPCA) today released an environmental assessment worksheet (EAW), draft air emissions permit, and State Implementation Plan (SIP) for a new proposed sewage sludge incinerator at the Metropolitan Council’s Metro Wastewater Treatment Plant near Pigs Eye Lake in St. Paul. The facility is the largest wastewater treatment plant in the state, handling more than 180 million gallons of wastewater and 850 tons of solids daily with its three incinerators.
The Met Council is planning to add a fourth incinerator to accommodate approximately 25% more wastewater created by expected population growth in the Twin Cities. Adding a new incinerator requires an amendment of the facility’s air emissions permit and site-specific State Implementation Plan, a requirement from the U.S. Environmental Protection Agency (EPA) due to the facility’s historic pollution of coarse particulate matter (PM10).
The EAW, air permit, and SIP all work together to assess the potential for significant environmental effects and put measures in place to protect the environment and nearby residents from air pollution generated by the new incinerator.
Environmental assessment worksheet
The EAW reviewed potential impacts on air, local geology, soils, groundwater, surface water, and other potential environmental impacts. Some key takeaways include:
- 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.
Air emissions permit and State Implementation Plan
Most air emissions from the proposed changes come from the incineration of sewage sludge. Since the fourth incinerator is similar in size and design to existing incinerators, the expansion is expected to create approximately 25% more emissions. The air permit requires the Met Council to install and maintain several controls to reduce emissions:
- 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 is also making minor changes to the State Implementation Plan, including specific air modeling. Historically, the concentration of PM10 in Ramsey County exceeded the 1987 federal limit. The EPA intervened and required a State Implementation Plan, which includes measures to improve air quality. The MPCA carried out a 20-year maintenance plan to meet these air quality requirements, and ambient air is now in compliance with EPA standards. The maintenance plan included issuing the Met Council air emissions permits and ensuring compliance. While the maintenance plan expired in September 2022, existing equipment at the facility must continue to adhere to the SIP conditions.
Community meeting to discuss changes
The public is encouraged to comment on the EAW, air permit, and SIP during the 45-day public notice period, starting July 11, 2023. The MPCA will host a public meeting for community members on August 14, 5:30-7:30 p.m., at Dayton's Bluff Recreation Center (800 Conway St., Saint Paul, MN 55106), with an open house and brief presentation on the draft permit, EAW, and SIP.
The MPCA invites residents, area businesses, and other interested parties to provide their valuable feedback during this public comment period. The agency encourages individuals to share their concerns, suggestions, and perspectives regarding the proposed fourth incinerator project and its potential impacts. All comments received will be thoroughly reviewed and considered as part of the decision-making process.
The public can review the draft EAW/air permit/SIP and submit public comments by visiting www.pca.state.mn.us/public-comments or by mail to:
- EAW: Minnesota Pollution Control Agency
c/o Katrina Hapka
520 Lafayette Road
St. Paul, MN 55155 - Air emissions permit: Minnesota Pollution Control Agency
c/o Bruce Braaten
520 Lafayette Road
St. Paul, MN 55155 - Site-specific State Implementation Plan: Minnesota Pollution Control Agency
c/o Megan Kuhl-Stennes
520 Lafayette Road
St. Paul, MN 55155
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