Helmut Ernst, chief engineer for Boston's Big Dig, reported that the persistent leaks of salty ground water into the tunnels has created structural and safety problems. "Tunnel leaks are a more vexing problem as they are widespread throughout the tunnel and are the cause of safety concerns and [have] a damaging effect on the tunnel structure and equipment," Ernst wrote. Ernst did not say the tunnel was unsafe. He estimated repairs and preventive measures would cost $150 million -- on top of $200 million that could be needed to rewire and replace corroded light fixtures in the tunnel.

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