Environmental Permitting, Special Topics in Environmental Management

EPA Finalizes 2021 Multi-Sector General Permit for Stormwater Discharges

On January 15, 2021, the EPA published its National Pollutant Discharge Elimination System (NPDES) 2021 Issuance of the Multi-Sector General Permit for Stormwater Discharges Associated with Industrial Activity (MSG).

Stormwater discharges, runoff

CCL STUDIO / Shutterstock.com

Key Points

  • The effective date for the permit is March 1, 2021.
  • New eligible dischargers must file a Notice of Intent (NOI) for permit coverage at least 90 days before beginning to discharge.
  • Those previously permitted under the 2015 MSG must submit a new NOI by the May 30, 2021, deadline.
  • Operators must prepare and implement new or revised Stormwater Pollution Prevention Plans (SWPPPs) before filing their NOI.
  • These new or updated SWPPPs must be filed with the NOI.
  • In the Agency’s original proposed changes to the permit, 12 key areas were identified to be changed from the 2015 permit, but in the permit’s prepublication version, only five key changes were identified.


The EPA’s prepublication notice includes the following changes:

  • The permit language was simplified and streamlined. It was also reordered: Monitoring is now followed by Corrective Actions and “Additional Implementation Measures” (AIMs), then SWPPP requirements.
  • There is a new requirement for signage to be posted about the permit, including information about the facility, how the public can obtain a copy of the facility’s SWPPP, and contact information for both the facility and the EPA in the event pollution is observed in the discharge.
  • A new Part requires “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.”
  • Monitoring changes, which include “indicator monitoring for pH, TSS (Total Suspended Solids), and COD (Chemical Oxygen Demand) for subsectors without benchmark monitoring; … indicator monitoring for polycyclic aromatic hydrocarbons (PAHs) for certain sectors/activities; … updating the benchmark monitoring schedule” and values; and impaired waters monitoring.
  • “[AIM] requirements for benchmark monitoring” in three tiers, with five exceptions:
    • “natural background sources,
    • run-on,
    • a one-time abnormal event,
    • 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, and
    • a demonstration that the benchmark exceedance does not result in any exceedance of an applicable water quality standard.”

Although both the New Mexico Environmental Department and the Massachusetts Department of Environmental Protection both filed comments requesting the addition of monitoring for per- and polyfluoroalkyl substances (PFAS), the EPA did not include this requirement.

In its prepublication notice, the EPA stated that updated sector-specific Industrial Stormwater Fact Sheets, including “practices that could be used by operators to minimize PFAS in stormwater discharges,” will be made available. To date, these have not yet been published.

Not including multiple appendixes, the entire permit is almost 250 pages in length, so there is a lot of information for companies to carefully review. For more information, see the EPA’s 2021 MSGP Permit website.

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