The Great Hill Tunnel, owned and operated by the South Central Connecticut Regional Water Authority, is a 100 MGD, 3,600-foot-long, 6-foot horseshoe-shaped raw water transmission tunnel that cannot be taken out of service and dewatered without installation of a bypass system. During 2017, routine tunnel leakage increased dramatically, causing concerns that known defects were getting larger and that increased leakage signaled impending tunnel failure. This paper discusses the rehabilitation program, which included manned inspection and repairs such as shotcrete, cement mortar patching, and contact grouting. It also compares the manned inspection with earlier ROV inspections of the tunnel.
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