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. In 2017-2018, the City is developed 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 Nov 12, 2018 at 10:24 AM

Frequently Asked Questions

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

Long Term Control Plan Update

As part of the 2017 Virginia Legislative Session, legislation was passed and signed by the Governor, that requires the City to remediate all of its combined sewer outfalls, requires that construction of future combined sewer infrastructure projects begin no later than July 1, 2023 and that construction of these projects be completed by July 1, 2025. The City, working together with Alexandria Renew Enterprises (AlexRenew), submitted a Long Term Control Plan Update to the Virginia Department of Environmental Quality (VDEQ) in May 2018. This Long Term Control Plan Update proposes the construction of a deep underground tunnel system to bring combined sewage to the AlexRenew wastewater treatment facility and will result in significant reductions in the number and volume of combined sewage discharged into City waterways. 

As of July 1, 2018, VDEQ has approved the Long Term Control Plan Update, concurring that the proposed combined sewer facilities will bring Alexandria's combined sewer outfalls into compliance with the 2017 legislation. Additionally, the City has transferred ownership of the four combined sewer outfalls located in the City to AlexRenew, who will be responsible for implementing the Long Term Control Plan Update as part of their RiverRenew Program.

For more information on the Long Term Control Plan Update, please contact Erin Bevis-Carver, P.E., Civil Engineer IV at 703.746.4154 or at More information about the RiverRenew program, can be found here.

City Council–AlexRenew Board Project Review Workgroup

In order to facilitate partnership between the City and AlexRenew and to provide a liaison for input and feedback, on June 26, 2018, City Council passed a resolution to establish the City Council–AlexRenew Board Project Review Workgroup. The workgroup includes two members of City Council, appointed by the Mayor, and two members of the AlexRenew Board. The purpose of the workgroup is to review and guide the plans, design, implementation, costs and financing of the CSO construction project with the intent of minimizing community impacts and maximizing community benefits.

Read more about the City Council–AlexRenew Board Project Review Workgroup.

Community Engagement

The RiverRenew Program is on track to comply with a 2017 state law requiring that remediation of its four combined sewer outfalls be completed by July 1, 2025. As part of the process of developing a Long Term Control Plan to meet the legislation, the City developed a Public Participation Plan in order to solicit input and feedback during the development of the plan. In June 2017, City Council convened an Ad Hoc Combined Sewer System Plan Stakeholder Group to help monitor the development of the plan. This Stakeholder Group met a total of seven times between October 2017 and April 2018. Additionally, the provided recommendations to City Council. Stakeholder Group meetings were open to the public and each meeting included a public comment period. Members of the public also had other opportunities to provide input and feedback, including a 30-day public comment period on the Draft Long Term Control Plan Update. As part of the RiverRenew program, there will be continued community engagement. For more information, please visit the RiverRenew Program webpage.

Read more about community engagement efforts.

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



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 Combined Sewer System (CSS), a legacy infrastructure built in the 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 CSS is located and the location of the combined sewer overflow (CSO) outfalls. The City owns and operates all of the sewers located in the CSS and Alexandria Renew Enterprises owns the CSO outfalls.

Overview Map of Combined & Sanitary Sewer System 

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

Combined Sewer System Annual Reports

Prior to July 1, 2018, the City owned the combined sewer outfalls. Operation of and discharges through these outfalls were regulated through the City's VDPES permit. As part of this permit, the City was required to 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 through 2017 are provided below. On July 1, 2018, the ownership of these outfalls was transferred to Alexandria Renew Enterprises.