USEPA’s 2021 Multi-Sector General Permit Updates – What it Means for the Primary Metals Sector

On January 15, 2021, the United States Environmental Protection Agency (USEPA) issued the 2021 Multi-Sector General Permit (MSGP) for industrial stormwater discharges. The MSGP became effective on March 1, 2021.


The USEPA established National Pollutant Discharge Elimination System (NPDES) permit requirements for industrial stormwater discharges in 1990; the agency first issued the MSGP for applicable facilities in 1995. The new MSGP requirements replaced the 2015 requirements on March 1, 2021.

The MSGP applies to facilities in areas of the country where USEPA is the NPDES permitting authority. This includes facilities in the following areas:

  • Four states: Massachusetts, New Hampshire, New Mexico, and Idaho
  • The District of Columbia
  • All U.S. territories except for the Virgin Islands
  • Federally operated facilities in Colorado, Delaware, Vermont, and Washington
  • Most Indian country lands
  • Other designated activities in specific states

While the MSGP is limited to these areas initially, many states are adopting significant elements of the MSGP as their individual state general permits get renewed.

From March 2, 2020, to June 1, USEPA offered a 90-day comment period for the proposed changes to the MSGP. During this same period, a total of 195 total comment letters and 1,895 unique comments were received and considered in the development of the new MSGP. The significant changes that were made to the 2021 MSGP process are highlighted below.

Significant General Changes in the 2021 MSGP

The following list summarizes the most significant changes to the 2021 MSGP:

  1. Streamlining of Permit: USEPA streamlined and simplified language throughout the permit to present the requirements in a more clear and readable manner.
  2. Public Sign of Permit Coverage: This requires MSGP operators to post a sign of permit coverage at a safe, publicly accessible location near the facility.
  3. Consideration of Stormwater Control Measure Enhancements for Major Storm Events: This requires that operators consider implementing enhanced stormwater control measures for facilities that could be impacted by major storm events, such as hurricanes, storm surge, and flood events.
  4. Monitoring Changes
    1. Indicator Monitoring for pH, TSS, and COD: A new provision requires operators to conduct indicator analytical monitoring of stormwater discharged to a water body for pH, total suspended solids (TSS), and chemical oxygen demand (COD) quarterly for the duration of the permit. This requirement applies to all operators in the following subsectors that do not have sector-specific benchmark monitoring requirements in the 2021 MSGP: B2, C5, D2, E3, F5, I1, J3, L2, N2, O1, P1, R1, T1, U3, V1, W1, X1, Y2, Z1, AB, AC, and AD. This monitoring requirement applies to Subsector F5 of the Primary Metals Sector (Sector F).
    2. Indicator Monitoring for Polycyclic Aromatic Hydrocarbons (PAHs): This new provision requires certain operations to conduct “report-only” indicator analytical monitoring for PAHs bi-annually during the first and fourth years of permit coverage. This applies to operators in all sectors with stormwater discharges from paved surfaces that will be sealed or re-sealed with coal-tar sealcoat, operators in sectors A, C, D, F, H, I, M, O, P, Q, R and S. This requirement includes the Primary Metals Sector (Sector F).
    3. Updating Benchmark Threshold Values: The benchmark monitoring thresholds for aluminum, copper for discharges to freshwater, selenium for discharges to freshwater, and cadmium is based on revised current Clean Water Act section 304(a) national recommended aquatic life water quality criteria. Additionally, the benchmark monitoring thresholds for magnesium and iron were suspended because of a lack of documented acute toxicity.
    4. Updating the Benchmark Monitoring Schedule: This requires that applicable operators conduct benchmark monitoring quarterly in their first and fourth years of permit coverage.
    5. Impaired Waters Monitoring: Operators discharging to impaired waters without an USEPA-approved or -established total maximum daily load (TMDL) must complete annual monitoring for discharges of certain pollutants to impaired waters. Monitoring is required for one year at each discharge point for all pollutants for which the waterbody is impaired, after which the operator can discontinue monitoring for the next two years for any pollutant that is not detected.
    6. Additional Implementation Measures (AIM): USEPA revised these AIM provisions to address concerns raised in public comments during the 2020 review period. The final MSGP requirements now provide a three-level structure of advancement and responses triggered by benchmark exceedances. The updated AIMs reduce costs and complexity by creating a stepwise, sequential advancement through the AIM levels with a clear “resetting” to baseline status if benchmark thresholds and responses are met within the required deadlines.

2021 MSGP Changes Impacting the Primary Metals Sector

Sector F – Primary Metals of the 2021 MSGP covers steel works, blast furnaces, rolling and finishing mills, iron and steel foundries, nonferrous metals, nonferrous foundries, primary smelting and refining of nonferrous metals, and miscellaneous primary metal products. Sector-specific requirements for the Primary Metals Sector are provided in Part 8, Subpart F of the 2021 MSGP. Key changes to the MSGP impacting the Primary Metals Sector are outlined below.

  1. Stormwater Control Measures for Major Storm Events: The requirement to implement enhanced stormwater controls for major storm events has been removed. The 2021 MSGP requirements allow facilities to consider implementing enhanced control measures for facilities that could be affected by major storm events, such as hurricanes, storm surge, and flood events. USEPA is not requiring operators to implement additional controls if the operator determines such controls to be unnecessary, but USEPA is requiring operators to consider the benefits of selecting and designing control measures that reduce risks to their industrial facility and the potential impact of pollutants in stormwater discharges caused by major storm events.
  2. Removal of Universal Benchmark Monitoring for pH, TSS, and COD: The requirement for universal benchmark monitoring for pH, TSS, and COD in the Primary Metals Sector has been removed. Instead, there will be non-benchmark (indicator) monitoring of those parameters required only for those subsectors that currently have no sector-specific benchmark monitoring requirements. Benchmark monitoring for pH, TSS and COD is required under Subsector F5 (Primary Smelting and Refining of Nonferrous Metals).
  3. Indicator Monitoring: Indicator monitoring for PAHs is required for all Primary Metals Sector (Sector F) facilities. Additionally, indicator monitoring for COD, TSS and pH is required for Subsector F5. PAH indicator monitoring includes the 16 individual PAHs identified at Appendix A to 40 CFR Part 423. The indictor monitoring is a “report-only” requirement. No thresholds or baseline values were established for these parameters.
  4. Modification of Copper Benchmarks: Benchmark monitoring for copper is required under the Primary Metals Subsectors F2, F3, and F4. The updated total recoverable copper benchmark for discharges to freshwater to 5.19 µg/L. The copper benchmark for discharges to freshwater were previously hardness-dependent.
  5. Modification of Aluminum Benchmarks: Benchmark monitoring for aluminum is required under the Primary Metals Subsectors F1 and F2 for discharges to freshwater. The updated benchmark for total recoverable aluminum was increased from 750 µg/L to 1,100 µg/L.
  6. Modification of AIM Requirements: The modification of the AIM requirements addresses some concerns posed during the comment period, by ensuring that a discharger has the opportunity to take compliance steps at one AIM level before being moved to the next level. All operators subject to benchmark monitoring requirements begin in the baseline status at the start of their permit coverage. An operator would progress linearly through the three AIM levels (AIM Level 1, Level 2, and Level 3) if an exceedance-triggering event occurs and continues. The operator is required to respond with increasingly robust control measures and continued benchmark monitoring with each subsequent AIM level. The following exceptions to the AIM requirements are offered in the 2021 MSGP for an exceedance-triggering event at any AIM Level:
    1. Natural background sources
    2. Run-on
    3. A one-time abnormal event
    4. A demonstration that discharges of copper and aluminum do not result in an exceedance of facility-specific criteria using the national recommended water-quality criteria in-lieu of the applicable MSGP benchmark threshold
    5. A demonstration that the benchmark exceedance does not result in any exceedance of an applicable water-quality standard
  7. Coal Tar Sealants: The restrictions on permit eligibility if a facility uses coal-tar sealants have been removed. The indicator monitoring requirements for PAHs apply to all facilities in the Primary Metals Sector with stormwater discharges from paved surfaces sealed or re-sealed with coal-tar sealcoat, or that use or store creosote or creosote-treated wood in areas exposed to precipitation. The indictor monitoring is a “report-only” requirement in the first and fourth years of permit coverage. No thresholds or baseline values were established for these parameters.

What’s Next?

EHS Support anticipates as State NPDES permitting authorities’ MSGPs expire and require updating, the State agencies will update their respective MSGP permits to be in accordance with the USEPA’s 2021 MSGP. EHS Support recommends facilities in the Primary Metals Sector prepare for permit updates by reviewing their stormwater program, monitoring results and Stormwater Pollution Prevention Plans to ensure that facilities have developed proactive stormwater management programs to comply with increasingly demanding stormwater permitting requirements.

Learn More:

Our team of compliance experts can assist you with preparing your facility for the updates in the 2021 MSGP and can answer any questions you may have about this update. Please reach out to Brianna Sadoski for:

  • Questions related to changes to the 2021 MSGP
  • Compliance concerns with the 2021 MSGP
  • Assistance navigating new AIM Requirements
  • Any other MSGP related questions!



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