NYC Stormwater Design Manual


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 (NYS DEC) for the City’s Municipal Separate Storm Sewer System (MS4). (City of New York State Pollution Discharge Elimination System Discharge Permit). 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) requirements of the permit. While this is the first comprehensive MS4 Permit for NYC, the City has been implementing stormwater management activities and projects for many years under the SPDES Permits for its 14 Wastewater Treatment Plants (WWTPs).

The NYC MS4 Permit requires that the City have adequate legal authority to implement and enforce a newly created Stormwater Management Program (SWMP). A review by the City conducted in 2016 concluded that the New York City Charter provides adequate legal authority to the Mayor and mayoral agencies to manage their operations and facilities, and to ensure coordination and information sharing for the City’s compliance with the MS4 Permit.

Project Applicability

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:

    1. Contributes runoff to the NYC MS4 System; AND

    2. Involves construction activity that results in ? 1 acre of land disturbance.

All projects that meet both of the above criteria are required to obtain a stormwater construction permit and a stormwater maintenance permit from NYC DEP (See Chapter 2). The definition of development and redevelopment for projects within NYC will follow the standards and associated.


Rules for the Use of Municipal Storm Sewer System

On June 20, 2018, NYC established the rules for the use of municipal storm sewer system. 1.3.b No Net Increase Requirements in MS4 Areas Local Law 97 provided authority to DEP and other city agencies to publish rules necessary to implement the MS4 Permit. Additional stormwater management requirements, specific to the POCs for each impaired waterbody, are needed to meet the no net increase requirements of the MS4 Permit. Details on the NNI process are shown in Figure X, which identifies the specific requirements to satisfy an NNI approach for each pollutant of concern in an impaired waterbody. Additional details on how the SMP design process incorporates the NNI requirements are provided in Chapter 3