National Park Service and DC Water hold public comment period for Clean Rivers Project to protect Piney Branch

January 06, 2023
Photo of CSO 049 in Rock Creek Park

Washington, DC - The National Park Service and DC Water invite the public to comment on a proposed project to improve water quality in Piney Branch, a tributary of Rock Creek. DC Water proposes to build a 4.2-million-gallon underground combined sewer overflow (CSO) storage tunnel to capture sewage, combined with stormwater, that would otherwise overflow into Piney Branch during heavy rains. 

In the late 19th and early 20th centuries, the sewer systems were built to carry both stormwater and sewage in the same pipe, which works well in dry weather. But during heavy rains, the pipes fill to capacity. To prevent flooding of streets and residences, the system includes overflows to allow the mixture of sanitary sewage and stormwater to overflow to the nearest waterway. These are called combined sewer overflows, or CSOs.

The proposed project would include construction of a diversion structure at the Piney Branch outfall, known as CSO 049, to redirect sewer flows to the storage tunnel and eventually convey the combined sewage to DC Water’s Blue Plains Advanced Wastewater Treatment Plant for treatment when the pipes and system can handle the volume. The project would reduce the volume of untreated sewer discharges into Piney Branch by an estimated 96% and reduce the frequency of discharges from 25 events per year to one event on average. DC Water seeks to control these overflows to improve water quality as part of the DC Clean Rivers Project.  

This project is needed to reduce sewage overflows that contribute to poor water quality in Piney Branch and ultimately the Potomac River and the Chesapeake Bay; and to comply with the 2005 Federal Consent Decree entered into by DC Water, the District of Columbia, the US Environmental Protection Agency, and the US Department of Justice, as amended January 2016. More information on the Clean Rivers Project can be found at More information on this project can be found at

The public is invited to provide input regarding issues and concerns associated with implementing the project. Feedback can be provided from January 18 to February 16, 2023 and will be used to refine project designs and to support the analysis of environmental impacts in an Environmental Assessment that will be prepared to comply with the National Environmental Policy Act. The public is also encouraged to submit comments on historic preservation issues to support compliance with the National Historic Preservation Act.

Engaging with the public is a critical part of the preliminary engineering and planning process. Anyone interested in learning more about the project and providing input can participate in the following ways:

Virtual Public Meeting: DC Water will be hosting a public scoping meeting on Wednesday, January 18, at 7:30 pm Eastern Standard Time (EST) using GoToWebinar. The meeting will last approximately one hour and there will be an opportunity to submit questions. You can access the meeting several ways.

  1. At the time of the meeting, go to on your computer or mobile device and enter the Webinar ID: 565-700-747 and your email. If you do not have GoToWebinar, you will be prompted to install a small file to your computer or download the app on your mobile device.
  2. You can call into the meeting (no video) using the toll-free phone number (877) 568-4108 and Audio Access Code 955-186-999.
  3. The meeting will be recorded and posted online at for anyone unable to attend the live session.

Submit Comments: Comments can be submitted online until 11:59 pm February 16, 2023 at If you prefer to mail your comments, make sure they are postmarked by 11:59 pm EST February 16, 2023 to receive consideration. Mail comments to the following address:

    Rock Creek Park 
    RE: Piney Branch Sewer 
    3545 Williamsburg Lane NW 
    Washington, DC 20008

Additional opportunities for public input will be available as the project continues.

Please be aware that the entire comment submitted – including personal identifying information such as address, phone number, and email address – may be made publicly available. Requests to withhold such personal identifying information from public release will be considered, but there is no guarantee that it will be withheld.

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