Combined Sewer System

The City's combined sewer system comprises approximately 540 acres and is located in the Old Town area. During most wet weather events, combined sewage (mixture of wastewater and stormwater runoff) discharges through one of four outfalls into receiving waterways. The City is developing a plan to reduce the impacts of combined sewer discharges on the environment. More information about the City's combined sewer system and current planning efforts is provided below.

Page updated on Aug 30, 2017 at 11:22 AM

Frequently Asked Questions

View answers to frequently asked questions about the City's combined sewer system remediation projects.

Community Engagement

The City of Alexandria encourages residents to participate in public process for the development of Long Term Control Plan Update over next three years that will help bring long-term improvements to Alexandria's sewer system infrastructure, improve water quality, and meet new regulatory requirements. Comments and input should be provided to Erin Bevis-Carver, P.E., Civil Engineer IV, Sanitary Infrastructure Division, Transportation and Environmental Services at 703.746.4154 or at

May 30 Public Information Meeting

The City held a public information meeting on Tuesday, May 30, at 7 p.m., to share information about how the new project deadline impacts the Combined Sewer System Long Term Control Plan Update submitted to the Virginia Department of Environmental Quality in December 2016. A copy of the staff presentation and a link to the video recording of the meeting are below. A summary of the meeting's question and answer period will be made available soon.

Read more about community engagement efforts. 


There are two types of storm sewer systems in the City of Alexandria, a separate sewer system, and a combined sewer system.  Separate sewer systems consist of two pipes: one pipe conveys stormwater runoff (rain water) from storm drains to local waterways with little or no treatment to remove pollutants.  The other pipe conveys sanitary sewage to a local wastewater treatment plant (operated by Alexandria Renew Enterprises).

In contrast, Combined Sewer Systems (CSS) have only one pipe which conveys both sanitary sewage and stormwater to a local wastewater treatment plant. About 540 acres in the Old Town is served by a combined sewer system, which was designed to carry sewage from inside homes and businesses and stormwater runoff from streets, rooftops, and parking lots in a single pipe—a "combined sewer." During dry weather, all raw sewage flows to the treatment plant operated by Alexandria Renew Enterprises. When it rains, the pipes can become overloaded with polluted stormwater. This mixture of stormwater (about 90%) and raw sewage may overflow into local streams through one of the four permitted combined sewer outfalls.

CSS Separate Sanitary and Stormwater Systems CSS Combined Sewer System

The City's Combined Sewer System (CSS), a legacy infrastructure built in 19th and early 20th century, is a combination of storm and sanitary sewer systems serving approximately 540 acres in Old Town. The map below shows where the City's CSS is located and the location of its combined sewer overflow (CSO) outfalls.

Overview Map of Combined & Sanitary Sewer System 

  Read more about the history of Alexandria's combined sewer system. 

Long Term Control Plan Update

The City submitted the Long Term Control Plan Update to the Virginia Department of Environmental Quality (VDEQ) for approval on December 2, 2016. This document incorporates VDEQ's comments on the draft document that was submitted in August 2016. In addition, this final document incorporates City Council's action at the November 9, 2016 City Council Legislative Session to accelerate addressing the combined sewer outfall that discharges into Oronoco Bay. This acceleration called for the following with respect to the Oronoco Bay outfall:

  • Committing in the Long Term Control Plan Update to perform a feasibility study during the upcoming permit cycle (2018-2023), 14 years ahead of current draft plan.
  • Committing in the Long Term Control Plan Update to perform an assessment starting in 2026, six years ahead of current plan.
  • Enhanced funding in the CIP for sewer separation and green infrastructure.

Read more about the Long Term Control Plan Update.   

Ad Hoc Combined Sewer System Plan Stakeholder Group

On June 23, 2015, Alexandria City Council approved a resolution to establish an Ad Hoc Combined Sewer System Plan Stakeholder Group (Stakeholder Group) to assist in monitoring the development of the Long Term Control Plan Update for the City's combined sewer system. This Long Term Control Plan Update is required by the Virginia Department of Environmental Quality (VDEQ) to meet new permit requirements and is due to VDEQ by August 23, 2016. The Stakeholder Group provided input to staff on a proposed recommended plan to VDEQ, including considerations on the City's budget, meeting environmental goals, and minimizing impacts to the community. The Stakeholder Group convened its final meeting on Thursday April 7, 2016 at 7:00 PM. Following the final meeting, the Stakeholder Group submitted a memorandum to the Mayor and members of City Council summarizing their input during the development on the Long Term Control Plan Update and recommendations for moving forward.  

Read more about the Ad Hoc Combined Sewer System Plan Stakeholder Group. 

Combined Sewer System Annual Reports

As part of the City's VDPES permit for its combined sewer system, the City must submit to VDEQ an annual report on operation and maintenance activities in the combined sewer system by March 31st of each year.  Annual reports for Calendar Year 2013 and subsequent years are provided below.