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SOURCE - Winter 2016

LAKE MEAD INTAKE NO. 3 Comes On Line Construction of Low Lake Level Pumping Station Underway SNWA Project Manager Erika Moonin, Director of Engineering Marc Jensen, and Deputy General Manager Dave Johnson in front of the tunnel boring machine cutterhead at the end of the Lake Mead Intake No. 3 tunnel. More and more, communities are building infrastructure, not to bring in more water, but to secure existing supplies. ON SEPTEMBER 26, 2015, LAKE MEAD INTAKE NO. 3 went into service. Approved in 2005 by the Southern Nevada Water Authority (SNWA) Board of Directors, its purpose is to protect existing water system capacity and provide ac-cess to better quality lake water in the face of continuing drought on the Colorado River. 18 SOURCE winter 20156 —Erika Moonin, Southern Nevada Water Authority Intake No. 3 Project Manager Primary components of the $500 million design-build project included a 600-foot deep shaft, three-mile 20-foot diameter intake tunnel and an intake riser structure at the lake bottom. It took eight months to construct the 1,400-ton structure on a 110-foot wide by 160-foot long barge of modular pontoons, and approximate-ly 36 months to bore the intake tunnel through rock at a depth that ranged from 587 feet at launch to approximately 50 feet at the intake structure base. Given economic constraints, the low lake level pumping station originally planned as part of the project was deferred to the future. Instead, plans called for the new in-take to be connected to the pumping stations at Intake No. 1, which can pump down to a level of 1,050 feet and No. 2, which can pump down to 1,000 feet. That future has arrived as water levels in Lake Mead have continued to drop with per-sistent drought on the Colorado River. In De-cember 2014, the SNWA Board authorized construction of a 900-million gallons per day (MGD) low lake level pumping station to en-sure access down to 875 feet (20 feet below the 895 feet dead pool elevation and the point at which Hoover Dam can no longer release water downstream). The $650 million project will require excavation of a new 20-foot diameter, 500- foot deep access shaft to a large underground forebay and drilling of 34 well shafts to house the 30 MGD submersible pumps, which will be able to operate at a minimum of 875 feet. Twenty pumps, plus two standbys, will discharge flow into a piping manifold located at the surface, then into a surge tank that will connect via a 144-inch diameter aqueduct to deliver water to SNWA’s Alfred Merritt Smith Water Treatment Facility. The other 10 pumps, plus two standbys, will discharge water via a 144-inch aqueduct, which will deliver it to


SOURCE - Winter 2016
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