A nearly five-year journey that took place as deep 460 m (1,590 ft) below the San Bernardino mountain range in southern California concluded on Aug. 20 when a 137-m (450-ft) tunnel boring machine (TBM) emerged from under the mountains. The TBM left behind a 6.1-km (3.8-mile) tunnel as part of a large-diameter regional water line that will help improve the quality and reliability of imported water serving nearly 19 million southern Californians. As part of the Metropolitan Water District's Inland Feeder project, the Arrowhead West tunnel, between Waterman and Devil canyons, is the last major piece of the 1.2-billion dollars project that was designed to boost southern California's supply. The breakthrough marks a major step in completing a 71-km (44-mile) water line.
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