Allison Creek Hydroelectric

LOCATION:  Valdez, Alaska   |   OWNER:  Copper Valley Electric Association
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This design-build project is located in Valdez, Alaska, near the Valdez Marine Terminal, which is the terminus point of the Trans-Alaska Pipeline System. It evolved from a 70-foot-high (21 m) (with an additional 50 feet [15 m] buried) rock-fill embankment dam at the outlet of Allison Lake with a conventional intake and buried/surface penstock, to a run-of-river project with a diversion structure further downstream and a powerhouse capable of producing 6.5 MW of electricity per hour for CVEA’s customers at peak production.

The purpose of this project was to divert water from Allison Creek via a diversion structure at an elevation of 1,300 feet (396 m) into a penstock that will carry the water 7,000 feet (1.25 miles or 2,130 m) to a powerhouse near tidewater. This new hydroelectric plant brings CVEA’s hydropower production portfolio from 50% to 64% and reduces its dependence on diesel generation plants by 750,000 gallons (283,905 L) of diesel. Upon completion, this project will reduce annual fuel generation costs by $2.4 million and eliminate 12,000 tons (10,886 t) of carbon dioxide annually.

In 2012, McMillen Jacobs began performing the FERC coordination, permitting and environmental support, all civil, structural, mechanical and hydraulic engineering and site layout, and acted as engineer of record. We also developed the geotechnical design for the powerhouse, penstock, diversion structure, and tunnel design for the access tunnel. Later, our role was expanded to include self-performed construction. Since then, we have continued to provide design-build services on this $54 million hydroelectric project. On the portions of work that McMillen Jacobs is not self-performing, our team is providing construction management services as owner’s representative of CVEA.

Scope of work includes:

  • Mobilization/demobilization in a remote area of Alaska
  • Detailed geotechnical investigations and hydrological and hydraulic analysis
  • Clearing and grubbing site which was thick with trees and bushes
  • 2 miles of access roads in steep, remote terrain (lower-access road to downstream tunnel portal; Powerhouse access road; and upper-access road to the diversion structure)
  • Installation of the 6.5 MW generator and pelton wheel turbine
  • In-stream diversion and intake structure requiring approximately 1,200 cubic yards (1,560 m3) of concrete
  • Access tunnel through solid rock: 780 feet long x 16 feet wide (221.0 x 4.9 m) x 16 feet tall (4.9 m)
  • 7,000 feet (1.25 miles or 2,130 m) of 36-inch (915 mm) and 40-inch (1,015 mm) large-diameter steel penstock
  • 60 x 70 foot (18 x 21 m) powerhouse building with a 70-foot-long concrete tailrace
  • New substation
  • Earthwork and blasting
  • Procurement support
  • 3.5 miles (5.6 km) of high voltage transmission line connecting new power generated from Allison Creek to existing Dayville Substation
  • Cast-in-place concrete structures (i.e. water diversion structures, etc)
  • Developing and implementing programs for safety, employee training, and security
  • Development building operational manuals
  • Environmental compliance, fish sampling, and water testing
  • FERC licensing support
  • Cost estimates and scheduling support