MS4 Pollution Prevention/Unified Stormwater Rule

The following documents provide guidance for the activities that require PP/GH activities to be implemented, which are based on the NYC MS4 Permit. Contractors are required to submit a certification that they will follow the MS4 Permit requirements prior to beginning the project and a certification at the completion of the project that they followed those requirements.

Effective June 1, 2019, New York City has been required to administer the Municipal Separate Storm Sewer System Permit (MS4) for the NYS Department of Environmental Conservation (DEC). The NYC Department of Environmental Protection (DEP) is responsible for administering the permit and collecting all documentation for compliance with the permit. All relevant projects are to be reviewed at the start of design to see if they are within the MS4 area. To reduce combined sewer overflows (CSO) due to storm events, the DEP implemented the Unified Stormwater Rule (USWR) effective February 15, 2022, that applies to projects in both MS4 and combined sewer areas. Detailed information with links can be found on the DEP's Unified Stormwater Rule webpage. The USWR requires Stormwater Pollution Prevention Plans (SWPPP) for all projects with a soil disturbance over 20,000 SF or new impervious areas over 5,000 SF and implementation of Green Infrastructure for such projects.

The MS4 Construction and Post Construction Fact Sheet provides a quick reference of the history behind the permit and what is required. 

The DEP's Municipal Separate Storm Sewer System webpage has detailed information with links to reference material. It also includes an interactive map of the MS4 drainage area, used to determine if a project is within the permit area. If a project site is near the MS4 area, designers are to submit a water-sewer request form, as the MS4 area is being actively increased and the map may not have been updated. In addition, the Division of School Facilities has created a DOE MS4 Sites list of existing school buildings under their jurisdiction that are within the area.

The USWR requires installation of Green Infrastructure, following the hierarchy outlined in DEP's NYC Stormwater Manual. Sewer applications for Covered Projects in both CSO and MS4 area are to be through DEP's USWR portal, though filing with the state is still required when there is over 1 acre of soil disturbance in an MS4 area. DEP has prepared a USWR Case Study to provide designers with guidance in preparing their submission to DEP.  The SCA has also created an SCA Green Infrastructure Design Guideline based on the DEP manual that indicates the possible candidates for Green Infrastructure and those that are not feasible for schools, as well as sample calculations.

In addition to the ongoing maintenance requirements of the MS4 Permit by the Department of Education, all contractors must follow the requirements of the MS4 Permit. Besides following Stormwater Pollution Prevention Plans and Sediment and Erosion Control to prevent soils from entering the system, contractors must follow and implement measures to meet the pollution prevention and good housekeeping (PP/GH) requirements of the permit. Chapter 7 of NYC Stormwater Management Plan highlights the items that need to be addressed.  Further, the DEP has created single page guidance documents of typical construction activities that would require PP/GH to be implemented with references to the applicable portions of the permit. These documents can be accessed on the Pollution Prevention/Good Housekeeping page.