Halfway Point of NY MS4 Permit: Roadmap for Municipal Compliance

New York’s current SPDES General Permit for Stormwater Discharges from Municipal Separate Storm Sewer Systems (MS4s), GP-0-24-001, became effective January 3, 2024 and runs through January 2, 2029. This puts regulated communities just past the halfway point of the current MS4 Permit cycle and is a great time to see if you are on track.

The permit is now well into implementation. At this point municipalities should be well beyond program development and should be actively implementing, documenting, training, inspecting and updating their Stormwater Management Program (SWMP).

Why MS4 Compliance Matters

New York’s MS4 Permit is fundamentally a water quality protection program. Stormwater flowing across roads, parking lots, construction sites, lawns, and other developed areas can pick up sediment, nutrients, oil and grease, road salt, bacteria, trash, and other pollutants. In many communities, that runoff enters the municipal storm sewer system and is discharged directly to a stream, river, lake, wetland, or other waterbody without first passing through a wastewater treatment plant or receiving other treatment. The MS4 Permit is intended to reduce those pollutant discharges to the maximum extent practicable with the ultimate goal of protecting water quality. For municipalities, that means compliance should increasingly be viewed as an ongoing municipal management program rather than an annual reporting exercise.

Six Minimum Control Measures Remain the Framework

Together, the following MS4 requirements are intended to prevent pollution at its source and reduce the amount of contamination ultimately reaching receiving waters.

• Public Education and Outreach
• Public Involvement/Participation
• Illicit Discharge Detection and Elimination (IDDE)
• Construction Site Stormwater Runoff Control
• Post-Construction Stormwater Management
• Pollution Prevention and Good Housekeeping for Municipal Operations

What should already be complete

• Permit coverage and initial SWMP updates: Following Notice of Intent (NOI) submittal to obtain ongoing MS4 Permit coverage, the most critical step is to develop an updated Stormwater Management Program (SWMP). The SWMP is the playbook for how MS4s will implement their stormwater program and is the key to compliance.
• Baseline Drainage System Mapping: Perhaps the most comprehensive new MS4 permit requirement is completion of drainage system mapping including outfalls (discharge locations to waterbodies), piping, ditches, manholes, catch basins, flow direction, interconnections and sewershed boundaries.  This mapping should be well underway to ensure permit compliance.
• Public access and reporting: A local stormwater contact and public reporting mechanisms for illicit discharges (i.e. non-stormwater discharges in the drainage system that could indicate pollution or other contaminant sources) and construction stormwater complaints should be established. Illicit discharge prevention information should be available to municipal staff, businesses and the public, and annual opportunities for public review and comment on the SWMP and draft Annual Report should be occurring. This is commonly accomplished by updating municipal websites with a stormwater information page including publicly accessible documents.
• Construction program: MS4s should have developed and implemented construction oversight procedures, an active construction-site inventory, construction-site prioritization, Stormwater Pollution Prevention Plan (SWPPP) review and inspection procedures, and enforcement tracking mechanisms.
• Post-construction program: A post-construction stormwater management practice (SMP) inspection and maintenance program should be developed and implemented. SMPs include permanent stormwater features (i.e. detention ponds, infiltration practices, rain gardens, or other drainage features) that are typically installed as part of new development projects to address flood and water quality protection.
• IDDE program: MS4s should have developed and implemented a monitoring program for potential illicit (non-stormwater) discharges to the municipal drainage system. Removing these discharges is a critical component to prevent pollution to receiving waterbodies.
• Municipal facilities: An inventory of municipal facilities should be developed (Highway/DPW facilities, salt storage locations, parks, fueling operations, etc).
• Ongoing reporting: Annual and interim progress reports should have been submitted and will be an ongoing permit requirement.

Upcoming Key Milestones

The January 2027 three-year milestone is a major step-up in program maturity. Municipalities should not wait until year-end to assemble the required mapping, monitoring-location inventory, facility prioritization, catch basin information, training records and an updated public education program. These elements often require coordination across engineering, highway/public works, planning/building, code enforcement, GIS and municipal administration.  Additional efforts will also be required in upcoming years to develop site specific SWPPPs for high-priority municipal facilities, complete comprehensive drainage system mapping, continue outfall inspections, ongoing public education outreach and regulatory reporting requirements, establishing a catch basin inspection program, construction and post-construction monitoring, and ongoing updates to their SWMP.  Although a lot of work has been done, more remains.

Important Applicability Note

The dates and milestones outlined above are generalized with GP-0-24-001 remaining the controlling regulatory compliance tool.  Requirements will also vary for traditional versus non-traditional operators and for MS4s subject to enhanced impaired-water or watershed improvement requirements.

For more information regarding the NYSDEC MS4 Permit or stormwater management compliance, please contact Vice President of B&L’s Environmental department, David Hanny.