Enhancing Resiliency and Increasing Redundancy for a Regional Water Authority: Adding Isolation Valves on Large-Diameter Transmission Main

The Great Lakes Water Authority (GLWA) operates and maintains a regional water supply system that spans seven counties in southeast Michigan and serves nearly 40% of Michigan's population. Much of this water supply system consists of large-diameter water transmission mains (WTM) up to 120 in. in diameter. An important facility in the regional system is a 96-in. diameter WTM that serves approximately 1,000,000 people, which conveys potable water from the Lake Huron Water Treatment Plant to the northern portions of the regional water supply system. The 96-in. WTM was constructed between 1965 and 1967 and consists of approximately 32 mi of 96-in. AWWA C301 embedded steel cylinder prestressed concrete cylinder pipe (PCCP). GLWA is currently relocating approximately 2.5 mi of the 96-in. WTM to improve access for operations and maintenance and to enhance the resiliency of the water supply system. In addition to the relocation of a portion of 96-in. WTM, two locations were selected to install new isolation valves, replace member partner connections, and construct large vaults to provide access for operations and maintenance. These new isolation valves include bi-directional bypass lines that will enhance system resiliency and increase redundancy by providing GLWA with the capability to isolate portions of the 96-in. WTM while maintaining water services to nearby member partner communities from either side of the new isolation valve. This paper will explore the additional operational flexibility these valves provide GLWA, the increased benefits to GLWA's water supply system, the challenges associated with designing large valve vaults around the valve configuration, and the challenges with siting large valve vault structures in a highly urban/suburban setting.