Lower Mill Creek contract awarded for Project Groundwork

Black & Veatch announced on 8 November that it has been awarded the design contract for the Lower Mill Creek Tunnel in Cincinnati, Ohio.

The proposed USD 244M tunnel will be 1.2-miles (1.9km) long and 30ft (9.1m) in diameter. It is expected to have a capacity of 33M US gallons (150M litres).

The tunnel will be part of ‘Project Groundwork’, which, valued at approximately USD 3.3bn, was laid out to reduce combined sewer overflows in Cincinnati by 85 per cent. Currently these exit to local waterways including the Ohio River.

Geotechnical investigations have begun to find the optimal route and depth of the tunnel. Detailed design is expected to begin in 2011. Construction should be completed in 2018.

Black & Veatch presented the thinking behind tunnel usage to solve the sewage problem:

Less energy use than traditional conveyance methods. The tunnels are largely built to enable gravity to

pull water across long distances to a central treatment facility, reducing energy consumption.

Sewer overflows can be held in the tunnel system until ‘off-peak’ times, providing operational flexibility.

Tunnels are located hundreds of feet below ground, providing flexibility for future redevelopment at ground level.

Tunnels have minimal maintenance expenses when compared with conventional sewer technology.

The Metropolitan Sewer District of Greater Cincinnati has explored alternatives to tunnelling, including stormwater retention basins, source control solutions, rain gardens and stream separations.

Black & Veatch is also contracted to design the pumping station for moving wastewater from the tunnel to treatment works