MPCA Finalizes New Industrial Stormwater General Permit, Including First-Ever PFAS Requirements

Originally published in the July 2025 issue of Bench & Bar of Minnesota Environmental Law Update, Minnesota State Bar Association.

Co-authored by Allison Opheim, Summer Associate

Effective June 1, 2025, the Minnesota Pollution Control Agency (MPCA) finalized its 2025 Multi-Sector General National Pollutant Discharge Elimination System (NPDES)/State Disposal System (SDS) Permit MNR050000 regulating the discharge of industrial stormwater (general permit). The new general permit controls pollution generated from rain and snow melt runoff (i.e., stormwater) associated with industrial activities discharging into waters of the state of Minnesota.

The final version of the general permit contains notable changes from the former industrial stormwater general permit (issued in April 2020), including new water-quality monitoring requirements for certain per- and polyfluoroalkyl substances (PFAS). The final general permit also pulls back some requirements included in MPCA’s draft version of the permit, published on 1/27/2025. Most notably, the draft permit would have required entities seeking a no-exposure exclusion to monitor for PFAS compounds, which would have represented the first time no-exposure applicants would have been subject to stormwater sampling requirements. However, the final general permit does not require facilities seeking no-exposure certification to monitor for PFAS. (No Exposure Policy Change).

Background

Under the federal Clean Water Act, a NPDES permit is required for stormwater discharges associated with industrial activity for any primary SIC code and/or narrative activities and co-located industrial activities as defined in 40 CFR § 122.26 (b)(14)(i-ix and xi). See also Minn. R. 7090.3010, subd. 1 (NPDES/SDS permit requirement for industrial stormwater) and 7090.0080, subp. 6 (adopting federal definition of “industrial activity” by reference). MPCA implements the NPDES permit program in Minnesota. Twenty-nine industrial sectors are covered by the regulation, based on primary standard industrial classification (SIC) code. Entities within these 29 sectors must either obtain a NPDES general permit from MPCA or apply for a no-exposure exclusion.

A no-exposure exclusion is available where there is “no exposure” of industrials materials and activities at a regulated industrial site to “rain, snow, snowmelt, or runoff.” (Minn. R. 7090.3060). To qualify for a no-exposure exclusion, the owner/operator of a facility must certify that all industrial materials and activities at the facility are either indoors or under a storm-resistant shelter.

New Provisions Related to PFAS

The finalized general permit includes several changes from the 2020 version, including, for the first time, requirements to sample for PFAS compounds for select SIC codes within the 29 sectors of industry included in the general permit requirement. Now, roughly half of the industrial sectors regulated by the general permit (as listed in Appendix D of the permit) must complete and implement an Industrial Stormwater PFAS Monitoring Plan, following an MPCA template.

Facilities subject to the PFAS monitoring requirement under the general permit must collect stormwater samples for at least four calendar quarters following the permittee’s date of coverage (the quarters do not need to be consecutive). If the averaged result from four quarterly samples is at or greater than the thresholds set in the general permit, then the permittee must implement a PFAS Source and Exposure Reduction Plan (SERP). Sampling must be conducted in accordance with the U.S. EPA’s Method 1633.

The general permit’s PFAS threshold levels are lower for facilities within one mile of a Class 1 surface water (protected for domestic use) or a drinking water supply management area (DWSMA, as defined Minn. R. 4720.0221).

For facilities within one mile of a Class 1 Water or DWSMA, MPCA has established monitoring values for five PFAS compounds. The threshold is set at 4 ng/L for PFOS and PFOA, and 10 ng/L for PFHxS, PFNA, and HFPO-DA (aka GenX chemicals). For all other facilities, MPCA has established a 10 ng/L threshold for PFOS and PFOA but does not require monitoring of PFHxS, PFNA, and GenX chemicals.

While the Fact Sheet for the draft general permit indicated that entities applying for the no-exposure exclusion would be subject to PFAS monitoring, MPCA dropped this requirement in the final general permit, writing that “facilities with a SIC code associated with PFAS seeking no exposure certification are not required to monitor for PFAS at this time.”

New Provisions Unrelated to PFAS

Other notable provisions in the final general permit include but are not limited to the following:

• More Frequent Stormwater Pollution Prevention Plans (SWPPP) Updates: The final permit requires permittees to amend their SWPPP within 30 days upon the occurrence of specific events, including (a) a change in design, operation, or maintenance at the facility that affects stormwater management; (b) discovery that a monitoring location is within one mile of an impaired water; (c) additional stormwater control measures and best management practices are needed to meet applicable water quality standards or to address benchmark value exceedances; and (e) an unauthorized discharge from the facility.
• Management of runoff: Under the final general permit, permittees must install and maintain stormwater outlet protection measures to prevent erosion at all areas where stormwater is discharging from the Permittee’s operational control.
• SWPPP Requirements for Special and Impaired Waters: The SWPPP must contain volume reduction and/or pollutant concentration reduction best management practices, designed to restrict industrial stormwater discharges to the designated special and/or impaired water.
• More specificity on benchmark monitoring locations: The final general permit specifies that permittees must select benchmark monitoring locations that are (a) located after the final down-gradient best-management practice but prior to discharging from the permittee’s operational control; (b) minimizes or eliminates sampling of stormwater from off-site sources; and (c) yields a sample that best represents the contribution of pollutants the permittee is required to monitor and receives discharge from an area of industrial activities and significant materials exposed to stormwater.

For more information, please see MPCA’s final general permit, updates and new requirements document, and related materials, including information on applying for coverage through MPCA’s e-Services portal, on MPCA’s website, at https://www.pca.state.mn.us/business-with-us/industrial-stormwater.

For more information, contact Jeremy P. Greenhouse.