The Metropolitan District has completed a $138 million pump station that will bring the South Hartford Conveyance and Storage Tunnel closer to full operation in Hartford and West Hartford, Connecticut.
MDC marked the milestone with a ribbon-cutting ceremony on October 1, 2026. The pump station forms a critical part of the four-mile underground tunnel system, which will capture and temporarily store combined wastewater and stormwater during major rain events.
The facility will move flows collected in the tunnel to the Hartford Water Pollution Control Facility for treatment. MDC completed the tunnel itself before the pump station, but the system could not become operational until the pumping infrastructure was finished.
The South Hartford Conveyance and Storage Tunnel extends beneath Hartford and West Hartford at roughly 200 feet below ground. The 18-foot-diameter tunnel can hold approximately 41.5 million gallons of combined sewer overflows.
Construction start
The tunnel began construction in 2019, when the tunnel boring machine Iris started excavating from the Hartford Water Pollution Control Facility. Iris completed the four-mile drive on January 4, 2022, reaching a retrieval shaft on Talcott Road in West Hartford.
MDC awarded the original tunnel construction contract to a Kenny Construction and Obayashi joint venture for approximately $279.4 million. The final tunnel construction cost reached about $335 million after approved change orders, according to MDC.
The tunnel and pump station form part of MDC’s broader Integrated Plan/Clean Water Project, a multibillion-dollar wastewater infrastructure program focused on reducing combined sewer overflows. MDC says improvements already completed under the program have eliminated more than 500 million gallons of annual CSO discharges.
Project financing
The pump station project received financing through Connecticut’s Clean Water Fund. State funding documents put the project’s total estimated cost at approximately $138.7 million, including about $66.5 million in grants and $72 million in low-interest loans.
The pump station contract includes more than the pumping equipment itself. The project encompasses the tunnel pump station and control building, screening facilities, odor-control systems, a head tank and force main, emergency generators, site restoration and wetlands mitigation.
The broader tunnel system also includes deep shafts and underground connections that collect flows from the existing sewer network. MDC’s tunnel project uses the underground storage capacity to hold storm-driven flows before the wastewater treatment plant processes them.
With the pump station now complete, MDC has reached the latest major construction milestone for the South Hartford tunnel system. The facility is intended to help reduce combined sewer overflows into local waterways, the Connecticut River and ultimately Long Island Sound.
The South Hartford tunnel project is another major U.S. investment in underground wastewater infrastructure. In Cleveland, the Big Creek Tunnel is also advancing as part of the Northeast Ohio Regional Sewer District’s Project Clean Lake program, adding another large-diameter tunnel to the growing network of projects designed to reduce combined sewer overflows.
Project Factsheet: South Hartford Conveyance and Storage Tunnel and Pump Station
- Location: Hartford and West Hartford, Connecticut
- Pump station cost: $138 million
- Pump station estimated project cost: $138.7 million
- Tunnel length: 4 miles
- Tunnel diameter: 18 feet
- Tunnel depth: Approximately 200 feet
- Storage capacity: 41.5 million gallons
- Latest milestone: Pump station construction completed and ribbon cutting held October 1, 2026
- Tunnel contractor: Kenny Construction and Obayashi joint venture
- Original tunnel contract: Approximately $279.4 million
- Final tunnel construction cost: Approximately $335 million
- Tunnel engineer: AECOM
- Construction manager: Jacobs
- TBM: Iris
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