CT DEEP Reissues the General Pretreatment Permit for Non-Significant Industrial User (NSIU) Discharges

The Connecticut Department of Energy and Environmental Protection (CT DEEP) has announced the reissuance of the General Pretreatment Permit for Non-Significant Industrial User (NSIU) Discharges to Publicly Owned Treatment Works (POTWs). This permit was officially released on 10/29/25.

The NSIU Pretreatment Permit complements the reissuance of the General Pretreatment Permit for Significant Industrial User (SIU) Discharges, governing industrial wastewater discharges from facilities classified as Non-Significant Industrial Users. NSIU facilities are typically smaller or have lower-volume discharges that still generate process wastewater subject to pretreatment standards.

Who does the permit apply to?

Similar to the SIU Pretreatment Permit, the NSIU Pretreatment Permit applies to industrial facilities that discharge process wastewater to a municipal sewer system (POTW) but do not meet the flow or pollutant loading thresholds of Significant Industrial Users. Covered facilities may include:

• Small manufacturing operations
• Maintenance shops
• Laboratories or testing facilities
• Other businesses that generate intermittent process water

What changes does the update include?

The reissuance of the NSIU GP represents an update to the previous permit, which was called the “Miscellaneous Industrial Users General Permit” (MIU GP). The MIU GP expired on 10/31/25.

Facilities that were authorized to discharge under the MIU GP must submit a renewal notification under the new NSIU Pretreatment Permit once registration opens on 12/1/25.

If your facility was covered under the previous version of this permit, you must register for the updated NSIU GP by 3/1/26.

How can Walden help?

If your facility discharges wastewater to a POTW or if you need help determining if you qualify as an NSIU, Walden’s EHS specialists can verify your applicability, prepare your registration package, and ensure that your operation remains in compliance. Call us today at 860-846-4069.