The USD 1bn project is the largest repair in the 175-year history of the city’s drinking water supply. The project will repair two areas of leakage within the 85-mile Delaware Aqueduct, the longest tunnel in the world, DEP said. The primary leak will be eliminated through the construction of a 2.5-mile (4km-) bypass tunnel, which will be drilled 600ft (182.8m) below the Hudson River from Newburgh to Wappinger.

Contractor Kiewit-Shea Constructors (KSC) is deployed a Robbins single shield TBM, 6.8m in diameter. The machine is built to withstand 30 bar of pressure—believed to be the most of any TBM ever manufactured, DEP said. The machine needs to withstand that much pressure because workers encountered huge inflows of water under immense head pressure when the aqueduct was first built more than 70 years ago.

Tunnel diameter will measure 14ft (4.2m) with a steel liner and a second layer of concrete. Once finished the tunnel will be connected to structurally sound portions of the existing Delaware Aqueduct to convey water around the leaking section—an approximately six-month-long shutdown planned for October 2022. The leaking stretch will be plugged and permanently taken out of service.

Just shy of two years ago the DEP held a ceremony on September 8, 2017 to mark the start of tunnelling, with the lowering of a TBM into a 845ft (257m) deep chamber.