Unified Stormwater Rule

DEP adopted the Unified Stormwater Rule (USWR) which represents a comprehensive update to the City's stormwater management policies, aiming to address both water quantity and quality requirements across combined (CSS) and separate sewer (MS4) areas. Refer to Chapters 31 and 19.1 of Title 15 of the Rules of the City of New York.

Effective February 2022, the USWR integrates and enhances existing stormwater regulations. The USWR applies to all development projects, defined as any public or private development that disturbs 20,000 square feet (approximately 0.46 acres) or more of soil or creates 5,000 square feet (approximately 0.11 acres) or more of new impervious surfaces, such as rooftops, sidewalks, and pavements. These projects must adhere to stringent stormwater management requirements to mitigate the impact of runoff. Key mandates include the preparation of a comprehensive Stormwater Pollution Prevention Plan (SWPPP), which details stormwater management measures such as site maps, construction drawings, soil testing results, and erosion control practices.

The USWR emphasizes the use of retention-based Stormwater Management Practices (SMPs) like bioretention, rain gardens, and permeable pavements to effectively manage stormwater on-site. SMPs are designed to protect, restore, or mimic the natural water cycle within built environments by retaining, detaining, and/or treating stormwater runoff. For more information and guidance, consult the NYC Stormwater Manual, which provides technical guidance for developers, designers, and engineers working with DEP on stormwater permitting.

Visit the NYC DEP Stormwater Permit webpage. To simplify the submittal and approval process, DEP has created an online project application system, the Stormwater Permitting and Tracking System, which enables applicants to submit a SWPPP and Stormwater Construction Permit application, as well as to follow the status of DEP’s review.

USWR Requirements for Right-of-Way Projects

Pursuant to the USWR and as detailed in the NYC Stormwater Manual - Chapters 6 and 7, projects located within the right-of-way are subject to specific requirements that differ from non-right-of-way sites. Milling and paving operations do not require an SWPPP or Stormwater Construction Permit. Drainage assets must be protected and erosion and sediment control measures along with pollution prevention measures must be implemented as appropriate. For more details review Chapter 7 of the NYC Stormwater Manual.

For roadway reconstruction and other ROW construction please refer to Chapter 6 of the NYC Stormwater Manual. The same disturbance (20,000 square feet or more) or impervious surface (5,000 square feet or more) thresholds apply and trigger the need to prepare a SWPPP. ROW projects the disturb less than one acre of soil will only require an SWPPP with erosion and sediment controls (ESC). Projects that disturb more than one acre of soil will have varying SWPPP requirements based on the type of development activity – Review tables 2.2 and 2.3 in the NYC Stormwater Manual and may require ESC’s and Post-Construction Stormwater Management Practices (PC SMPs). For ease of reference, common roadway construction activities are:
 

   **PC SMPs are required only when the project disturbs one acre or more of soil 

Please note activities that do not disturb soils, such as surface markings of paved areas are not considered in the estimation of the extent of the disturbed area for purposes of USWR. Stormwater Permitting and Tracking System

Additionally, where the following criteria is met, projects must provide a pollutant load analysis in the SWPPP that demonstrates adequate controls are in place such that the change in pollutant loading will not result in a net increase (NNI). 

• Disturbed area is 20,000 sf or more
• Project is located in an MS4 area (MS4 Interactive Map is available to assist applicants)
• Project discharges to an impaired waterbody, and
• Project results in an increase in impervious area

Projects Requiring PC SMPs

(Refer to Section 6.3 of the NYC Stormwater Manual for the latest requirements)

For right-of-way (ROW) projects that disturb 20,000 square feet or more of soil but do not increase impervious area, designers have three options for meeting water quality goals:

1. Reduce existing impervious area by at least 25% of the total disturbed, impervious area.
2. Manage a minimum of 25% of the Water Quality Volume (WQv) from the disturbed, impervious area through SMPs.
3. Pursue a combination of the two approaches above.

As a first step, projects must seek to reduce existing impervious areas. This can be achieved using:

• Planted areas (review Landscape)
• Tree plantings (review Tree Beds)
• Pervious paving materials such as pre-cast porous concrete panels (review Materials)

Early consultation with DEP is encouraged to determine whether impervious area reduction goals can be met. Note that Soil Restoration criteria in Section 5.1.5 of the New York State Stormwater Management Design Manual must be applied to all newly created pervious areas.

Where goals cannot be met by reducing impervious areas, ROW projects have a limited number of SMPs that may be used to manage the WQv due to several unique challenges of working in the ROW. The following table notes the SMP’s that may be pursued in the ROW. Note that the SMPs listed are ordered in a preferred practice hierarchy. Designers should evaluate the feasibility of SMPs in this order, however, each location must be assessed for its unique siting constraints. 

Designers should refer to the latest DEP Standard Designs and Guidelines for Green Infrastructure Practices for the layout and configuration of each system. Review Precast Porous Concrete Panels and Planted Stormwater Management Practices for more information.

In addition, if there is an existing SMP located on the site that captures and treats runoff from the impervious area being disturbed, then the condition and size of the SMP shall be evaluated. If the SMP is able to manage the appropriate WQv as-is, then use of that SMP may be continued. Otherwise, designers need to consider additional SMPs or changes to the existing SMP to meet the requirements above. 
ROW projects that cause an increase in impervious area must manage 100% of the WQv from the newly created impervious areas. The remaining disturbed areas may be managed using one of the three options noted above. 

Additional Considerations
Per Chapter 2 int he NYC Stormwater Manual, any project located in an MS4 area that meets the Construction General Permit requirements will also have to go to DEC for review.

Projects that cannot meet technical requirements noted herein must schedule a consultation with DEP before proceeding with the SWPPP application. As part of the meeting, DEP and the designers will review opportunities and other potential considerations for meeting water quality objectives.