Is Your Community Ready for MS4 Mapping Requirements?

The current New York State Department of Environmental Conservation (NYSDEC) Municipal Separate Storm Sewer Systems (MS4) General Permit 0-24-001 has been in effect for nearly two years, and this means that Phase 1 of comprehensive stormwater system mapping will be due in January of 2027. Below we examine who needs to map their MS4 systems, what the Phase 1 mapping requirements consist of, and what the intent is behind this component of MS4 permit compliance.

Who do the MS4 mapping requirements apply to?

The mapping requirements apply to the following MS4 operator types:

• Traditional Land Use Control: A city, town, or village that possesses land-use control authority (i.e. zoning authority)
• Traditional Non-Land Use Control: Typically a county-level governmental entity, such as a county department of public works, without the authority to directly impose land-use regulations
• Non-Traditional: Includes publicly-owned properties such as state university campuses, military bases, state-owned hospitals, public K-12 schools, etc.

Phase 1 mapping requirements

There are general mapping requirements applicable to all MS4 operators, and additional requirements for MS4 operators which discharge to waters impaired for phosphorus, silt and sediments, pathogens, nitrogen, and/or floatables. Our discussion here is limited to the general mapping requirements that apply to all MS4 operator types.

Mapping of the following items are required in Phase 1 of this permit:

• Stormwater monitoring locations, with designated priority
• Preliminary storm-sewershed boundaries for newly-designated MS4 operators
• Focus areas, which include:
  • Areas that discharge to waters with a classification of AA-S, A-S, AA, A, B, SA, or SB
  • Areas that discharge to impaired waters
  • TMDL watersheds
  • Construction activities
  • Zoning districts
  • Stormwater hotspots
  • Illicit discharge areas
• Publicly owned/operated post-construction stormwater management practices
• Municipally-owned facilities

Why is mapping important?

NYSDEC believes mapping is important to ensure the MS4 operator has an understanding of the MS4’s geographical extent. The mapping is a helpful tool when used for community planning, identifying potential water quality improvement projects, and identifying specific areas for future development or conservation. It can also help inform zoning code updates or changes. In addition, mapping identifies sampling locations in the event there is a spill or illicit discharge into the MS4 system, in order to better determine the discharge source.

However, the utility of MS4 system mapping extends beyond the DEC’s stated needs. While the mapping provides a comprehensive inventory of outfalls, system components, waterways, and other system features, the actual process of mapping the system will provide operators with a clear picture of the current state of their systems. This can help in the identification of needed repairs and prioritization of ongoing maintenance items, and educate town residents and property owners about their municipality’s storm sewer system.

If you need assistance mapping your storm sewer system or would like to explore possible grant funding options for MS4 mapping services, contact Walden’s stormwater experts at 516-980-5508 today! If you are interested in learning more about stormwater management, download our guide here.