Four-Mile Treatment Plant – Contract 2

Completed in 1980 by Mole Constructors, the Four-Mile Treatment Plant – Contract 2 project encompassed about 3,300 linear feet of tunnel and 4,000 linear feet of open cut. It utilized a 97-inch Lovat Tunnel Boring Machine and employed ribs and boards for support. The tunnel accommodated 60-inch reinforced concrete pipe and traversed glacial moraine comprising sands, gravel, and silts at depths of 40 feet to 50 feet below the water table. Annulus backfill grouting with molcrete was applied as well.