Municipal Separate Storm Sewer System

A municipal separate storm sewer system (MS4) is a publicly-owned conveyance or system of conveyances (including but not limited to streets, ditches, catch basins, curbs, gutters, and storm drains) that is designed or used for collecting or conveying stormwater and that discharges to surface waters of the State. Separate storm sewers carry stormwater runoff directly to local waterbodies and serve approximately 30–40% of New York City.

As stormwater flows over streets and other impervious surfaces, it sweeps up pollutants such as oils, chemicals, pathogens, and sediments. In separate sewer areas, this pollution is carried by stormwater runoff and discharged directly into the City’s waterways. This can have a negative impact on water quality and recreational uses.

For information about the combined sewer system, which is used by about 60% of New York City, visit Combined Sewer Overflows.

MS4 Permit

The City of New York received its first MS4 Permit on August 1, 2015. This permit is required under the Clean Water Act and is issued by New York State Departement of Environmental Conservation (DEC). The intent of the MS4 permit is for the City to implement measures to reduce pollution in stormwater runoff. The MS4 Permit significantly expands the City’s previous obligations to reduce pollutants discharging to the MS4. Numerous City agencies have significant responsibilities under the MS4 Permit. The New York City Department of Environmental Protection (DEP) is responsible for coordinating the interagency efforts to meet the City’s MS4 Permit requirements.

Download the Full MS4 Permit

Stormwater Management Program (SWMP) Plan

The MS4 Permit requires the City to develop a Stormwater Management Program (SWMP), which includes numerous programs designed to reduce pollution in stormwater.

The SWMP Plan describes the ways in which the City will satisfy the requirements of the MS4 Permit by managing stormwater discharges into and from the City’s separate storm sewers. Most chapters of the Plan include a description of any relevant existing City programs; new initiatives and/or program enhancements; and measureable goals for future assessment of the program.

The SWMP Plan was released to the public on April 4, 2018. The public was invited to submit comments on the SWMP Plan from April 4 through May 15, 2018. DEP also held two stakeholder meetings during the public comment period to provide background on the Plan and to accept verbal comments from meeting attendees. On August 1, 2018, DEP submitted NYC’s SWMP Plan to the New York State Department of Environmental Conservation (DEC).

MS4 Permit Deliverables

The Municipal Separate Storm Sewer System (MS4) Permit requires the City to submit several written deliverables to the New York State Department of Environmental Conservation (DEC). For a complete list of deliverables, please review the full MS4 Permit.


The NYC Stormwater Management Program: 2018 Draft MS4 Annual Report

Submission of the complete draft SWMP Plan, including all components identified in Parts II.B, III.A through D, and IV. Introduction and IV.A through J (Part IV. Introduction)


Stormwater Management Program Plan

Submission of the complete draft SWMP Plan, including all components identified in Parts II.B, III.A through D, and IV. Introduction and IV.A through J (Part IV. Introduction)


Integrated Sentinel Monitoring Report

Annual report on the Sentinel Monitoring Program with sampling results and information on field investigations. The report also includes information on unauthorized non-stormwater discharges.


Draft Procedures for No Net Increase

Proposal for programs to meet the MS4 permit requirement to reduce pollutants in impaired waters.


Draft Work Plan

Draft Work Plan to determine the loading rate of floatable and settleable trash and debris discharged from the MS4.


Updated Legal Authority Submission

Updated description of the City’s legal authority to control discharges to the MS4. This description includes details on Local Law 97 of 2017 which consolidates, clarifies, and supplements existing legal authority, to enable the City to act in a regulatory capacity to control pollutant discharges to and from its MS4.


2017 Progress Report

Progress reports on the development of the SWMP Plan, including public involvement/participation components.


2016 Progress Report

Progress reports on the development of the SWMP Plan, including public involvement/ participation components.


Legal Authority Submission

Description of existing legal authority to control discharges to the MS4.


Trash Free NYC Waters

Submit certification that an interim floatable and settleable trash and debris reduction media campaign has been developed with implementation schedule.


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