Persistent water seepage has prompted the contractor of a new “straw” at southern Nevada’s Lake Mead to drill a starter tunnel in a drier direction.
The contractor says it is investigating an alternate alignment roughly 20� east from the current 200-ft-long starter tunnel. The plan would be to eventually rejoin the original alignment.
Vegas Tunnel Constructors LLC (VTC), a joint venture of S.A. Healy Co., Lombard, Ill., and Impreglio S.p.A., Sesto San Giovanni, Italy, last year encountered water three times in six months while creating a starter tunnel for a $447-million, 3-mile-long intake that will draw water deeper from Lake Mead, now at 40% below capacity. Decades of boom growth and drought have sapped lake water supplies and threatened to shut Hoover Dam’s hydroelectric turbines by 2013.
The design-build project awarded in 2008 faces a one-year delay and tens of millions of dollars in added costs, according to Marc Jensen, engineering director of Southern Nevada Water Authority. A change order is being negotiated for the unexpected costs; the item will be discussed during a Feb. 17 water authority board meeting. SNWA has money for the change order, says Jensen, although insurance could cover some expenses.
VTC based its bid on over 50 owner-performed core samples. VTC project manager James McDonald says he has since taken another 10 core samples. “Underground construction has more uncertainty and greater risk than other types of construction.”