The East Bay Municipal Utility District’s Claremont Tunnel is an 18,000-foot long water tunnel built in 1929. The Claremont Tunnel Seismic Upgrade Project involved the construction of a bypass tunnel through the Hayward Fault zone, including an enlarged vault section designed to accommodate up to 8.5 feet of horizontal offset. Notable aspects include challenging and squeezing ground conditions, and a special excavation and support sequence.