The Indiana Department of Environmental Management (IDEM) issued and made effective the new Industrial Stormwater General Permit (ISGP) on December 30, 2025. This permit will replace the existing permit-by-rule, Title 327 of the Indiana Administrative Code (IAC) Article 15, Rule 6 (commonly referred to as “Rule 6”).
Some of the most notable changes from Rule 6 to the ISGP include benchmark monitoring requirements for total suspended solids, chemical oxygen demand, pH, and additional pollutants for certain industrial sectors. Facilities in some sectors will be required to test for the hardness of receiving waters to set benchmarks for specific metals. Additionally, the new permit establishes requirements for Stormwater Pollution Prevention Plans (SWP3), including more detailed maps and sections addressing the new monitoring requirements.
Once IDEM makes the Notice of Intent available, currently permitted facilities will need to apply for coverage under the new permit within 180 days. Permittees will be notified once the form is available. IDEM recommends facilities conduct the following actions prior to the issuance of the Notice of Intent forms:
- Review the changes from Rule 6 to the ISGP
- Obtain or test for hardness of receiving waters to which the facility discharges, if applicable
- Prepare or update the facility SWP3 to align with the ISGP
Facilities operating under a no exposure exclusion are not required to file a new form, and will be required to renew their no exposure certification 90 days prior to the current expiration date.
Further Information
Please refer to IDEM’s notice for more information on the new Industrial Stormwater General Permit.
Questions? We’re here to help
For support with your stormwater permit or SWP3, or to discuss any questions or concerns, please contact Katie Milk.
