Located up to 45m below ground, the main 6km-long, 5m-diameter tunnel with branches will be a deep reservoir for overflows of untreated water which otherwise would flow into local rivers during heavy rain.

The tunnel system will store the untreated water before it’s pumped to an upgraded wastewater treatment plant.

The client is the Allegheny County Sanitary Authority (Alcosan). It hopes the tunnel system will stop 7 billion gallons of untreated water contaminating regional waterways every year.

The team’s scope of work includes 8km of excavation work for tunnels and multiple shafts using a new tunnel-boring machine.

Two secondary tunnels, the 1.3km-long Chartiers Creek Tunnel and 500m-long Saw Mill Run Tunnel, will connect to the main tunnel and each measure 4m in diameter.

Surface works are also planned, including flow regulators, two technical buildings and a new river outfall. Webuild said surface infrastructure would have a minimal footprint.

Two other tunnels are planned as part of the Regional Tunnel System in Pittsburgh, the Allegheny River Tunnel and Monongahela River Tunnel.

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