Miners excavating from the Irvington Portal in Fremont and the Vargas Shaft – about 1,341m away – met underground after a 55-t roadheader holed through and connected the two headings. The tunnel is a vital piece of the San Francisco Public Utilities Commission’s USD 4.6bn improvement program to upgrade its entire aging Hetch Hetchy system.

Following last week’s hole-through, miners will prepare this tunnel section for the installation of the 2,590mm steel liner. The steel pipe will be installed in 15.2m sections and welded together inside of the tunnel. The remaining section of tunnel, stretching from the Vargas Shaft east to the Alameda West Portal heading in Sunol, is much longer and expected to hole through in the third quarter of next year.

The tunnel will stretch from Sunol Valley to Fremont’s Mission San Jose District, parallel to the existing Irvington Tunnel, which was built 80 years ago. The excavation began in May 2011 and is expected to be complete in May/June 2014.