Combined Sewer System FAQs

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

Page updated on Aug 20, 2018 at 3:45 PM
In a continuing effort to accelerate remediation of the City of Alexandria’s combined sewer system, the City is working with AlexRenew, the lead agency for the remediation program. To learn more about RiverRenew, AlexRenew's CSO remediation program, visit
What’s the problem?

While 95 percent of Alexandria is served by separate sewer systems for stormwater and sewage, the remaining 5 percent is served by a combined sewer system, in which stormwater and sewage flow into the same set of pipes. The area served by the City’s combined sewer system is comprised of about 540 acres in historic Old Town. During dry weather, all sewage flows to a wastewater treatment facility. When too much rain flows into the system, this mixture of stormwater and sewage overflows into local waterways at four outfalls.  Alexandria has one of the earliest combined sewer systems in the country, dating back to the early 1800s. More than 800 cities nationwide have similar systems, including neighboring outfalls that overflow into the Potomac River.

Combined sewer systems were once considered to be state-of-the-art and a significant achievement in public health. They protected people, especially in population centers, from diseases caused by bacteria and viruses.  The construction of wastewater treatment facilities resulted in further protection of public health.

However, combined sewer discharges negatively impact the health of the City’s waterways. In addition, there are now more people, more homes and businesses, more water use, and more paved and other impervious surfaces that cause stormwater runoff, increasing the amount of combined sewer overflows.  Today, combined sewer overflows occur about 60 to 70 times per year, during most rain events.

What will the remediation projects accomplish?

Remediation requires the planning, design, and construction of massive underground storage tanks and tunnels.  These storage facilities, some the length of a football field and many feet deep, will store the excess combined sewage when it rains.  After the rain ends, the system will pump the combined stormwater and sewage in the tanks and tunnels to the wastewater treatment facility at a manageable rate.  Overflows will only occur a few times per year, during the heaviest rains.

Is the City following the law?

Yes. The City’s four combined sewer outfalls already operate under state permits and comply with all federal and state laws, regulations, and permit requirements, including the federal Clean Water Act.  The City has never been subject to an enforcement order by any federal or state agency; all remediation projects have been conducted in consultation with regulators.

What has the City of Alexandria already done to address this issue?

The City has long worked to separate portions of the combined sewer system over time as new sanitary infrastructure was constructed, and since 2003 private developments have been required to assist with sewer separation. This has already reduced the volume of flow into the combined sewer system by about 10%. The City has also been implementing best operation and management practices and making system improvements so that as much wastewater as possible flows to the treatment facility.  

Through sewer fees paid by residents, businesses, and nonprofit organizations, the City has made substantial investments over time to operate, maintain, and improve its sewer infrastructure. This includes investments of $50 million in the last decade alone – including rehabilitation of approximately 60 miles of sewers (25% of the City’s entire system).

The City created a Long Term Control Plan to document its approach to remediating the combined sewer outfalls.  This plan was approved by the Virginia Department of Environmental Quality in 1999, and the City submitted an update in 2016 following two years of public meetings, hearings, and community engagement efforts.  City Council established a diverse stakeholder group charged with providing input in the development of the plan, including implications for the City's budget and how the Plan would accomplish the City's environmental goals and permit requirements while minimizing impacts to the community.  Unfortunately, the sudden enactment of a new state law in 2017 disregarded these plans and community processes, and the City is working to revise the Long Term Control Plan for resubmission to the state in the context of the new law.

When will the remediation projects be completed?

Pursuant to a state law enacted in 2017, the City must complete the work by July 1, 2025.  The City is committed to completing the projects as quickly as possible.

How much will these projects cost?  How will they be funded?

Remediating all four outfalls is expected to cost approximately $400 million.  In May 2017, the Alexandria City Council adopted operating and capital budgets providing $370.2 million in project funding. Revenue for these projects will come from significant increases in sewer-related fees over the following decade. The budgets also include the assumption of $45 million in state aid, similar to the assistance previously provided to other Virginia communities to address combined sewer outfalls in those cities.

How are sewer fees collected?  Will these charges go up?

Alexandria residents, businesses, and nonprofit organizations currently pay for sewer service as follows:

  • Alexandria Renew Enterprises (AlexRenew) is the independent public entity that collects and treats wastewater from Alexandria and parts of Fairfax County.  AlexRenew receives water usage information from Virginia American Water and uses it to calculate wastewater treatment fees billed by AlexRenew.

  • The City charges a sanitary sewer system capital investment and maintenance fee, which is calculated based on water usage and added to the AlexRenew bill.  This charge will increase by 30% as of July 1, 2017 (from $1.40 to $1.82 per thousand gallons), with significant additional increases expected over the next 10 years to fund combined sewer system remediation.

Isn’t Alexandria a wealthy enough city to fix this problem more quickly?

There are two misconceptions involved here:

First, the primary challenge to completing these projects is not money, but engineering, environmental permitting, and construction.  Massive underground storage tanks and tunnels must be designed, planned, and constructed for all four outfalls, and each project location requires a custom engineering solution.  This type of work is very different than building a new school or road, which are much more routine types of capital projects.  Due to the new state law, Alexandria must also execute these mega-projects simultaneously, instead of using the phased approach recognized by the U.S. Environmental Protection Agency and the Virginia Department of Environmental Quality.  Potential delays are also possible from permitting, contractor availability, environmental issues, archaeological artifacts, and other risks.  

Second, although Alexandria has one of the highest per capita incomes in the United States, this single figure is misleading.  While there are many wealthy residents that inflate the average, many others are not as fortunate.  For example, 58% of public school students in Alexandria are eligible for free or reduced school lunches on the basis of family income, and 13.5% of households are below the poverty line.  In addition, non-residential customers of every size pay sewer fees, including small businesses, churches, and other entities with limited financial flexibility  Like most major capital projects, the City will finance the combined sewer system remediation projects by borrowing money through the issuance of long-term municipal bonds.  These bonds will be repaid from increases in the sewer-related fees paid by residents, businesses, and nonprofit organizations.

How disruptive will the work be?

Given the scale of the projects involved, and the state-imposed deadline for completing them, work is expected to be very disruptive to neighbors.  Tens of thousands of trucks full of dirt will have to be removed from the worksites, and pile driving may take up to a year or more at each site.  The City is committed to mitigating the impact as much as possible.

Will the City’s plan eliminate all combined sewer system overflows?

No.  The City’s strategy, which has been adopted by hundreds of other localities faced with combined sewer remediation, is to store excess sewage and stormwater in underground tanks and tunnels when it rains, and then pump the contents back to the wastewater treatment facility at a manageable rate when the rain ends.  Based on Alexandria’s typical rainfall, there will likely be approximately four overflows per year when unusually heavy rain still exceeds the capacity of the storage tanks and tunnels. This proposed level of reduction in combined sewer overflows is consistent with, and in some cases better than, how other combined sewer communities are performing and is in accordance with the Combined Sewer Overflow Policy developed by the U.S. Environmental Protection Agency.

The only way to completely eliminate combined sewage overflows is to separate the sewage and stormwater pipes in the area still served by combined sewer pipes.  This would require digging up every neighborhood street in the Old Town area and building a completely new sewer system.  Not only would this dramatically increase the cost, but it would turn all of Old Town into a continuous construction zone for years rather than concentrating the work in specific locations.  

Once the City’s combined sewer system projects are complete, will the Potomac River be swimmable and fishable?
No.  The Potomac River is not healthy to swim or fish in because of high bacteria loads.  Alexandria’s combined sewer system is only responsible for about 2% of this bacteria, and this will drop to nearly 0% once the City’s projects are completed.  Most of the bacteria in local waterways is the result of stormwater runoff, wildlife, pet waste, and overflows from combined sewer systems in other localities.  Although Alexandria is doing its part to reduce the bacteria load in the local waterways through combined sewer system remediation and stormwater management projects, the other sources noted will continue to make it unhealthy to swim or fish in the Potomac for the foreseeable future.