On August 1, 2015, New York City (NYC) received a State Pollutant Discharge Elimination System (SPDES) Permit from the New York State Department of Environmental Conservation (NYSDEC) for the City’s Municipal Separate Storm Sewer System (MS4). The NYC MS4 Permit requires the City to implement measures to reduce pollution in stormwater runoff utilizing a number of programs, as detailed in the Stormwater Management Program (SWMP) Plan.

The MS4 permit required the City to evaluate reducing from 1 acre the threshold for projects that must comply with stormwater management requirements under the Construction and Post-Construction regulatory program. The City completed a study to determine the lower threshold that would apply to all MS4 projects. In addition, the City extended applicability of the Construction and Post-Construction requirements to the combined sewer areas of NYC to enhance water quality throughout the City.

New Development/Redevelopment Projects

The NYC MS4 permit requirements apply to any development or redevelopment project, whether public or private, that meets the following criteria:

      Disturbs 20,000 square feet or more of soil or creates 5,000 square feet or more of impervious surface

All projects that meet these criteria must obtain a Stormwater Construction Permit and, under certain circumstances, a Stormwater Maintenance Permit from NYCDEP.

Rules for the Use of Municipal Storm Sewer System

As of June 1, 2019, the City implemented 15 RCNY Chapter 19.1, Industrial, Commercial, Construction and Post-Construction Sources, which was updated on February 15, 2022.