The Lake Mead Intake No 3 project is shortly due to be awarded to the SA Healy/ Impregilo JV (T&TNA, Sept 2007, p6). Comprising 16,000ft (4.8km) of 20ft (6.1m) finished i.d. tunnel plus a 600ft (182m) deep access shaft and a deep intake shaft to the bottom of the lake from the tunnel horizon, the contract is said to be worth $450 million.
Blake Schmidt, spokesman for client Southern Nevada Water Authority (SNWA), told T&TNA it had “recommended Vegas Tunnel Constructors JV (SA Healy/Impregilo) to be presented to the SNWA board of directors for award of 070F 01 C1 [Lake Mead No 3 Intake] in March.”
The $650 million project is part of SNWA’s Capital Improvements Program (CIP), which was approved at the end of 1995. The plan has four main components: Intake System Improvements; Water Treatment Improvements; Transmission System Improvements & Miscellaneous Improvements (mainly power). Reviewed annually, the CIP was significantly amended to include Intake No 3 in 2005. Currently the CIP is projected at $2.85 billion.
The Intake No 3 design was awarded to a JV of MWH and CH2M Hill and got underway in August 2005. Its $36.3 million contract spans 1,146 design days and is due to be complete by mid-September this year.
The new intake at 860ft (260m) asl will replace existing intakes should the surface of Lake Mead drop below 1050ft (320m) asl. Recently water levels have fallen significantly due to drought conditions across the western states. The new intake will also provide access to the better quality of water at deeper levels.
T&TNA was told that a precast concrete segmental lining would be employed on the tunnel, which it was claimed would be the deepest subaqueous tunnel constructed with a pressurized face TBM in the world to date. Hydrostatic pressures with present lake conditions are approximately 15 bar. If the lake level rises during construction this could rise to 17 bar. Hyperbaric cutterhead interventions will be required.
Additional challenges will include the tunnel alignment crossing the old Las Vegas Wash Channel, a historic stream channel with reduced cover between the lake bottom and the tunnel crown.
SNWA is also requesting proposals for contract 070F 05 C1, connections and modifications to Lake Mead Intake No 2. The scope of work includes connection to the existing intake, such as a 22ft (6.7m) diameter x 380ft (116m) deep shaft; a 14ft x 16ft (4.3m x 4.8m) modified horseshoe tunnel 270ft (82.5m) long; and a 14ft x 16ft modified horseshoe tunnel 250ft (76m) long.
A pre-bid meeting is due for March 28, with bid opening on April 21. T&TNA has learnt bid package plans are being held by Ameron, Construction Notebook, Guy F Atkinson, Traylor Bros, Barnard Construction, Ferguson Waterworks and Sierra Plan Room.
Figure 1. Existing and planned Lake Mead intakes Fig 1 – Existing and planned Lake Mead intakes Falling water levels in the lake are immediately apparent Falling water levels in the lake are immediately apparent
