CT DEEP Releases Updated Commercial Stormwater General Permit

After more than a decade, the Connecticut Department of Energy and Environmental Protection (CT DEEP) has released an updated Commercial Stormwater General Permit (CSGP). The new permit introduces updated requirements for facilities with extensive paved areas (such as shopping centers, business parks, schools/universities, and retail complexes) and emphasizes improved site management, documentation, and pollution prevention practices. The permit complements CT DEEP’s Industrial Stormwater General Permit, which applies to manufacturing and industrial operations. Walden previously posted a blog discussing the industrial permit and its applicability; many facilities that fall outside that scope may now need to register under the CSGP.

Overview and Applicability

The CSGP regulates the discharge of stormwater from certain commercial sites such as malls, movie theaters, and supermarkets, to surface waters of Connecticut. The most recent version was issued on October 1, 2025, and becomes effective December 1, 2025, with an expiration date of September 30, 2030.

The permit applies to commercial sites that meet the following criteria:

• Those with 5 or more acres of contiguous impervious cover.
• Sites with eligible Standard Industrial Classification (SIC) or North American Industry Classification System (NAICS) codes found in Appendix A of the permit.

Basic Compliance Requirements

Sites that are covered under this permit will generally need to implement the following to comply with the permit requirements:

1. Submit a registration – including fee payment, site information, discharge details, and more.
2. Develop a Stormwater Management Plan (SMP) – similar to the Stormwater Pollution Prevention Plan (SWPPP) required by the Industrial Stormwater Permit, this plan should identify impervious surfaces, outfalls, pollutant sources, and best management practices.
3. Implement control measures – sites must implement practices to minimize pollutants in their stormwater discharge.
4. Monitoring requirements – sites are required to conduct periodic visual inspections and annual analytical sampling.
5. Recordkeeping and training – the permittee must certify that the SMP and registration are accurate, maintain inspection and maintenance records, and train employees.

Additional requirements may apply depending on a facility’s SIC/NAICS classification, discharge location, or if the site drains to an impaired waterbody. Each facility should carefully review the full permit to determine its specific obligations.

Registration Deadlines

CT DEEP has established the following registration deadlines for the 2025 CSGP:

• Existing permittees (previously covered under the old permit) – must register by April 1, 2026 (within 120 days of the effective date). Interim coverage is provided by DEEP.
• Newly covered sites (not previously registered) – must register by December 1, 2026 (within one year of the effective date).
• New commercial developments beginning after December 1, 2025 – registration is required at least 60 days before stormwater discharges commence.

How Walden Can Help

Many commercial sites with large impervious areas will be required to register for this permit. Understanding whether your property is subject to the new CSGP, preparing a compliant registration package, and developing an effective SMP are essential steps to maintaining compliance.

Walden’s EHS team can help determine applicability, prepare site plans and SMPs, conduct staff training, and complete permit registration submissions. Call us today to learn more about our stormwater services at 516-980-5508.