Project Value: $145M

The new Walnut Hill Water Treatment Plant in Marlborough performs several major treatment processes, including primary and secondary disinfection, pH level adjustment, and fluoridation. Water enters the plant from the Hultman Aqueduct’s Cosgrove Tunnel, flows through the Ozonation Building, the Treatment and Post-Treatment Buildings, and into the storage tank, from where it ultimately makes its way through the MetroWest Water Supply Tunnel to Metropolitan Boston’s homes and businesses.