Why Build a Regional Tunnel System?

The regional tunnel system is a critical component of the Clean Water Plan aimed at improving and protecting the water quality of the region’s streams and rivers. Watch the video or read more to learn about the system and its benefits!


About the Regional Tunnel System

The new regional tunnel system will capture wet weather combined sewer flows and move them to the plant for treatment. It will consist of three major tunnel projects. The Ohio River Tunnel (ORT) project is the first of the three projects. The other two projects are the Allegheny River Tunnel (ART) and the Monongahela River Tunnel (MRT). The ORT will be implemented concurrent with the new Wet Weather Pump Station.


Allegheny River Tunnel

Learn More about the Allegheny River Tunnel project

Ohio River Tunnel

Learn More about the Ohio River Tunnel project

Monongahela River Tunnel

Coming Soon

New infrastructure will redirect excess rainwater to a treatment facility via regulators, consolidation sewers, drop shafts, and tunnels. The system, mostly 120-150 feet underground, also includes a storage tunnel.

The proposed facilities will tie to the existing combined sewer system and divert excess wet weather flows away from the outfalls, moving them instead to the treatment plant.

The facilities will include:

  • New regulators that will send the excess flow through consolidation sewers to drop shafts
  • New drop shafts to bring wet weather flows deep underground
  • New connector tunnels to the tunnel
  • And, finally, the new wet weather tunnel that will convey flows to the new pump station at the treatment plant (and will also act as storage)

Most infrastructure will be below ground with tunnels sitting at about 120-150 feet below ground.

Tunnels and Near-Surface Facilities

The new facilities will include over 16 miles of wet weather tunnel, 40 regulators, and 31 shafts as well as about 4 miles of consolidation sewer. These facilities will connect to the existing combined sewer system, which includes similar facilities consisting of approximately 31 miles of deep tunnel interceptors, over 200 combined sewer regulators and associated shafts, and 13 access shafts.

Regulators

CWP_regulator

Regulators are underground structures that are built along existing sewers to control where sewage is sent. Regulators allow normal dry weather flow to continue to the existing sewer network but during wet weather they divert flow to drop structures and into the tunnel via consolidation sewers.

It is anticipated that these regulator structures will be sized from 6-feet by 12-feet to 28-feet by 50-feet.


Consolidation Sewers

Consolidation/Connector SewersConsolidation sewers are sewers that convey some of the combined sewage to the drop shafts that then transfer the flow to the main tunnels. Consolidation sewers avoid building additional drop shafts and long connections to the main tunnels.

Consolidation sewers are anticipated to range between 24-inches and 144-inches in diameter with depths ranging between 10-feet and 50-feet below ground. Depending on conditions at the location the consolidation sewers could be built using micro-tunneling techniques or an open-trench approach.

Drop Shafts

CWP_dropshaft

Drop shafts are deep, vertical structures that transfer the combined sewage from the surface to the tunnels.

Their design includes hydraulic structures to manage the flow as it drops and to dissipate the energy generated to prevent damage to the drop shaft and the tunnels. The drop shafts are anticipated to range between around 15 feet and 50 feet in diameter depending on location.

The size of the construction area depends on the diameter of the drop shafts. Typically, an acre is required for safe and efficient construction.

After construction, once the hole is covered, only access for maintenance activities is required.

Deep Tunnels

Tunnel system

The new deep tunnels are underground structures designed to convey the combined sewage from the drop shafts to the new wet weather pump station for treatment at ALCOSAN’s wastewater treatment plant (WWTP) during wet weather events. At times the tunnel system will temporarily store excess flow until it can be treated at the WWTP.

The main tunnels will primarily be constructed using large tunnel boring machines (TBM) that will be lowered from the surface and later retrieved via construction shafts.


 

The tunnel system, starting with the Ohio River Tunnel, begins construction in 2025 and completes by 2036. Initial designs for the ART start in late 2024 and MRT in 2025. Project timelines may adjust as work progresses.
The implementation of the tunnel system will span 15 years and must be completed by the end of 2036.


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Frequently Asked Questions

The regional tunnel system is a critical component of the Clean Water Plan (CWP), which was adopted to meet the requirements of the Federal Modified Consent Decree and improve and protect the water quality of the region’s streams and rivers.
No, the tunnel system is adding new conveyance capacity to deliver combined sewage flows during wet weather events to the ALCOSAN wastewater treatment plant for treatment. The existing municipal and ALCOSAN sewers will continue to be utilized to transport sewage to the ALCOSAN wastewater treatment plant.
The new tunnel system is designed to last for at least 100 years. Operation and maintenance staff from ALCOSAN will be responsible for maintaining it. The tunnels will be accessed for maintenance via the access shafts.
Capturing “all” the overflows would not be affordable for the region. The tunnel system is configured and sized to capture enough of the combined sewer overflows to meet water quality objectives. The size of the tunnels was established in collaboration with the regulatory agencies.
The Clean Water Plan and the tunnel system is not intended to stop existing flooding conditions in the communities. The primary goal of the CWP and the tunnel system is to improve and protect the water quality of our rivers and streams.
Subsidence is not a concern along the ALCOSAN tunnel alignment because the tunnels will be located deep in bedrock.
ALCOSAN is a ratepayer funded authority and most of the CWP costs will need to be borne by the ratepayers. ALCOSAN’s rate strategy manages CWP cost impacts to ratepayers by implementing multi-year rate increases through 2036. ALCOSAN’s Board of Directors implemented a 7.0% annual rate increase for 2022 through 2026. ALCOSAN acknowledges the impacts of rate increases on low-income households and has increased the Clean Water Assistance Fund to $40/quarter. More information on the Clean Water Assistance Fund can be found at dollarenergy.org.
Sites will be restored to the existing condition at a minimum but may also be improved. Limited above ground facilities will be required as ALCOSAN will use the sites mostly to access the shafts and regulators via hatches and covers. As the design and construction of each tunnel progresses, ALCOSAN works with the community to determine potential opportunities for site enhancement following construction, which may include a paved surface or a cleared site for a greenspace.  
The new tunnel system must be constructed near existing sewers pick-up points to capture combined sewer overflows. This is a key factor in deciding on location of the proposed facilities. Other decision factors include environmental studies and geotechnical investigations.
Email ALCOSAN at ORT@alcosan.org with questions or comments about the regional tunnel system, including the Ohio River Tunnel.

The FAQs above include the most common questions we receive about the Regional Tunnel System, but there's much more to explore! Explore our additional FAQs and see how the Clean Water Plan is making a difference in your community.

  • Construction Schedule and Impact
  • Community Impact and Engagement
  • Economic Impact and Job Creation
  • Climate and Environmental Impact
  • The Ohio River Tunnel


Quick Links

Ohio River Tunnel

Allegheny River Tunnel

Monongahela River Tunnel

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