RiverRenew is a major program in response to a 2017 Virginia law to achieve cleaner, healthier waterways in Alexandria. RiverRenew features a new network of deep tunnels and sewers that will connect to the four combined sewer outfalls in Alexandria. These outfalls currently pollute our waterways on rainy days. The tunnels will capture millions of gallons of sewage mixed with rainwater for treatment at AlexRenew, and the cleaned water will be returned to the Potomac River.
In the oldest portions of Alexandria, sewage and rainwater is collected in one type of sewer system, called a combined sewer system. In a combined sewer system, there is one sewer pipe under each street that collects and transports both sewage and rainwater.
When it's not raining, these combined sewer pipes transport sewage for treatment at AlexRenew's wastewater treatment plant, called the Water Resource Recovery Facility. On rainy days, the capacity of these combined sewer pipes is often exceeded. When the combined sewers are full, the excess sewage mixed with rainwater overflows into Alexandria's waterways via four combined sewer outfalls. Currently, these overflow events occur approximately 60 times per year, resulting in bacteria, trash and other pollutants in local waterways, including Hooffs Run, Hunting Creek and the Potomac River.
In other portions of Alexandria, sewage is collected in a sewer pipe that is separate from the sewer pipe that collects rainwater. This type of sewer system is called a separate sewer system.
In April 2017, Virginia passed a law requiring Alexandria to remediate all four of its combined sewer outfalls by July 1, 2025. The law, Senate Bill 898, introduced by Senator Richard H. Stuart (District 28), lays out the mandates for RiverRenew to meet. The bill requires any combined sewer outfalls in the state, including Alexandria’s, to be brought into compliance with Virginia law, the federal Clean Water Act, and the U.S. Environmental Protection Agency’s Combined Sewer Overflow Control Policy.
On June 29, 2018, a joint Long Term Control Plan Update prepared by AlexRenew and the City of Alexandria, which outlined an approach to remediate Alexandria’s combined sewer system was accepted by the Virginia Department of Environmental Quality. The plan features the solution for Alexandria’s combined sewer issue that AlexRenew will implement through the RiverRenew program. The RiverRenew program includes the following major components:
- A two-mile-long tunnel system, constructed at approximately 100 feet below ground;
- New sewer infrastructure to connect the tunnel system to the existing combined sewer system; and
- Upgrades to the process for debris and bacteria removal treatment at AlexRenew.
Together, these components will allow for the capture, storage and transport of millions of gallons of combined sewage for treatment at AlexRenew, instead of overflow into Alexandria’s waterways. More information on the RiverRenew program, as presented to the community at a series of listening sessions in Fall 2018, can be found here.
RiverRenew will prevent millions of gallons of sewage mixed with rainwater from contaminating our rivers and streams. On average, 140 million gallons of sewage mixed with rainwater is discharged annually. With the new tunnel system in place, the RiverRenew program will reduce the number of overflows from an average of 60 times per year down to fewer than four per year. It is anticipated that the volume of sewage mixed with rainwater discharged on an average year will be reduced down to 16 million gallons. This reduction in the frequency and volume of discharges of sewage mixed with rainwater will limit the amount of bacteria, trash, and other pollutants flowing into Hooffs Run, Hunting Creek, and the Potomac River. Through RiverRenew, we can achieve safer waterways for our community, a healthier environment for our wildlife, and cleaner waterways for future generations.
Led by a five-member citizen board, AlexRenew is a special-purpose authority that has been serving the City of Alexandria and parts of Fairfax County for the last 60 years. AlexRenew treats an average of 35 million gallons of wastewater per day from more than 300,000 people at its water resource recovery facility, located in Alexandria’s southwest quadrant.
In keeping with our water protection mission, AlexRenew, with support from the City of Alexandria, will lead the planning and construction of RiverRenew to ensure its implementation by 2025. AlexRenew has demonstrated success in building and operating large-scale infrastructure. AlexRenew’s facility will serve as the main construction site for the proposed tunnel system to minimize community impact. Additionally, the combined sewer flows collected by the tunnel system will be delivered to AlexRenew’s water resource recovery facility for treatment.
Capital costs related to RiverRenew are estimated between $370 and $555 million. This estimate is based on a conceptual level of design.
Capital costs consist of engineering, management and construction costs.
Revenue for RiverRenew will come from increases in sewer-related fees. Rate increases per residential customer are currently estimated to be between $20 and $40 per month, on top of the current sewer bill. Additional funding from the Virginia Clean Water Revolving Loan Fund and potential state grants will be required to finance the RiverRenew facilities. In order to alleviate this significant financial burden, AlexRenew, with the City of Alexandria, has solicited funding from the Governor and the General Assembly for the program, similar to what has been provided for other Virginia communities with combined sewer systems.
A more detailed rate analysis is currently underway and anticipated to be complete in spring 2019. This analysis will more clearly quantify the forecast for ratepayers for this significant investment in cleaner water.
Planning and Design
RiverRenew is currently conducting an Environmental Assessment (EA) with the National Park Service (NPS) to analyze the potential impacts on the community and environment. The EA will ensure that natural resources, cultural resources, and community impacts are considered when locating proposed alternatives for the tunnel system.
Following a series of public outreach events, including three Community Listening Sessions and a Public Scoping Meeting with the NPS, RiverRenew sought input from the community and government agencies to guide analysis of the proposed alternatives. The public scoping comment period was open from September 10 - October 25, 2018.
Comments received from the scoping process will be incorporated into the analysis of the proposed alternatives. Once the EA is written, it will be circulated for public comment. The public comment period is currently anticipated for Spring 2019 and will include another series of Community Listening Sessions. RiverRenew and the NPS will respond to comments and conclude the process by documenting a decision.
The information and proposed alternatives for the tunnel system presented at the fall 2018 Community Listening Sessions and NPS Scoping Meeting can be found here.
The existing combined sewer pipe will be connected to the new tunnel system by building concrete connecting structures called diversion facilities. The portion of the diversion facility connected to an existing combined sewer pipe near the surface is designed to divert sewage mixed with rainwater into a vertical drop shaft. Flows travel through the drop shafts to the tunnel system below. The drop shaft will be designed to dissipate the energy of the falling water and remove air before it enters the tunnel. On a rainy day, these diversion facilities will divert millions of gallons of sewage mixed with rainwater into the new tunnel system for treatment at AlexRenew, instead of the existing combined sewer outfalls.
Check out this video of our scale-model drop shaft to see this process in action.
To build the new tunnel system, RiverRenew will use state-of-the-art tunnel boring machines (TBMs) which will:
- Allow us to build long tunnels deep underground without digging up major portions of the city;
- Dig out the soil deep below ground and install a new tunnel in the void that’s created; and
- Remove soil through the TBM and along the newly created tunnel, then lift it to the surface via an elevator at AlexRenew’s water resource recovery facility.
At present, there are several potential tunnel routes and alternative diversion facility locations. Detailed maps of the proposed alternatives can be viewed here.
Outfalls 001/002: This portion of the tunnel system will run east from AlexRenew’s water resource recovery facility to Outfall 002, and curve north to Outfall 001, located in Oronoco Bay Park. There will be two diversion facilities connected to this tunnel near each outfall site.
Outfalls 003/004: This portion of the tunnel system will run south from Outfalls 003 and 004, located beneath Duke Street and along Hooffs Run, and connect to AlexRenew.
Flow into the tunnel system will be routed to AlexRenew’s water resource recovery facility, where it will be cleaned and returned to the Potomac River.
RiverRenew is currently performing preliminary site investigations to help understand what is underground. This work includes collecting soil samples at select locations within the City of Alexandria. These subsurface explorations are called borings, and the data collected help us understand the conditions below ground to design and build solutions best suited to our local geology. You can learn more about these borings and our drill rigs here.
RiverRenew is also conducting survey work to determine the depth and location of existing utilities below ground. This work is necessary to confirm the location of utilities prior to any construction.
Yes, the performance under future climate conditions has been tested and the proposed solution incorporates an adaptable and resilient design.
No. While discharges of sewage mixed with rainwater will be significantly reduced as a result of RiverRenew, there is still a chance that overflows will occur during very heavy rains. Eliminating the combined sewer discharges would result in a tunnel size that pushes existing technology to its limit, greatly disrupts our Alexandria community, and substantially increases the total cost of the project without gaining any additional water quality benefit.
Construction at the AlexRenew Water Resource Recovery Facility to support RiverRenew will begin in June 2019.
Construction of the tunnel system will begin in 2021.
Under the 2017 Virginia law, construction to control combined sewer discharges must be completed by July 1, 2025.
Planning is still underway to determine the exact locations of construction, but a majority of the work is expected to take place at the AlexRenew Water Resource Recovery Facility. Additionally, construction disturbances are anticipated at or near the existing combined sewer outfall locations at Oronoco Bay, Hunting Creek and Hooffs Run.
The tunnels will be built deep below ground – approximately 100 feet – using a state-of-the-art tunnel boring machine that stabilizes the external soil and groundwater as it moves. This technology significantly minimizes the potential for ground movement, resulting in virtually no disruption at the surface.
In addition to the Environmental Assessment process, RiverRenew is also considering the effects on historic structures through the Section 106 process. Section 106 of the National Historic Preservation Act requires federal agencies to consider the impacts of their undertakings on any structure, site or district listed or eligible for listing in the National Register of Historic Places.
RiverRenew is actively coordinating with federal and state agencies, as well as City staff, the Alexandria Archaeological Commission, Historic Alexandria Resources Commission, and other consulting parties, to ensure Alexandria’s historic and archaeological resources are carefully considered and any potential adverse effects are appropriately mitigated.