Completing the Blue Lake expansion6 January 2015
Meeting the schedule, staying within budget and remaining upfront with, and active within, the local community has led to the successful completion of the Blue Lake expansion project in Alaska.
Just past noon on a rare sunny November day, a small group of very enthusiastic people gathered to cut a ribbon, flip a switch (actually touch a flat screen), and then listen for the roar of water entering a new 5.3MW turbine. This officially kicked off power generation from the City and Borough of Sitka - Alaska's new 15.9 MW powerhouse on the edge of Sawmill Creek.
The group in the new, highly computerised control room watched to see the red line that depicts the consistency of power delivery flatten out before leaving the room for celebratory cake. This moment had been two years in the works in terms of construction and many more preceding that in permitting and arranging financing.
"The wave of hydro's future is small projects like this one in Sitka," Barnard Construction Company, Inc. Superintendent Steve Alsept explained looking out over the 20m by 43m powerhouse. "They'll be more like run-of-the-river projects, at least in North America, less disruptive and producing decent power."
The group cutting the ribbon on 13 November 2014 stood with a golden shovel at the base of the Unit 5's 5.3MW horizontal Francis turbine/generator: standing in the same spot most of them stood just two years earlier to break ground. Despite many weather and logistics challenges posed by the location of this project on a small mountainous island along Alaska's southeast coastline, the project is wrapping up on schedule and within budget. As this article went to press, only punchlist items remained in the powerhouse and formwork removal at the dam.
When engineers designed the original Blue Lake Project over 50 years ago, they had planned for a third phase where the Blue Lake Dam could be increased by 7m. Now, at the completion of phase three, Sitka has pushed the engineering envelope and constructed a 25m dam expansion as well as a new powerhouse with three new turbines. This increase doubles the output of the original Blue Lake Dam and powerhouse, securing the future for hydro as the primary source of electricity for Sitka's 9000 residents and businesses.
From the outset, this Blue Lake Expansion Project required meticulous planning and scheduling. All equipment and materials were at least two weeks away by barge, generally via Seattle, Washington and Anchorage, Alaska, whether it was the 45 truckloads that comprised the Liebherr LR/1600 Crane or the 13,000 CY of concrete materials. The other significant logistical challenges were:
- The actual access to the work at the dam.
- Working in and around the significant amount of rain that falls in a typical year on Baranof Island (one storm system raised the lake by more than 3m over five days).
- Constructing the powerhouse foundation 6m below the immediately adjacent Sawmill Creek.
- Rehab of the 2.4m-diameter penstock in inaccessible locations.
The project raised the concrete arch dam to its geotechnically maximum height, which translated to adding 25m to the 44m dam, and reconstructed the intake by which the city would be receiving both its water and its power. Nearly all work had to be conductedthrough the reach of three cranes, including the largest operating in Alaska. The dam was accessible only from one side, which meant each day superintendents and foremen had to coordinate the movement of their crews and materials by crane.
The penstock, largely tunnelled, had to be reinforced. In exposed places, the 2.4m-diameter pipe could be replaced, but where it stood intact in solid rock, it had to be reinforced internally. The three existing tunnel portals had steel liners that extended into the unlined portions of the tunnel. These liners had to be extended to protect the penstock from increased pressure due to a higher lake level. The liner extension required that the teampull in collapsed pipe sections used hydraulic jacks to round out the pipe, weld the longitudinal joints of each section, weld each section together, and finally grout the annular space between the tunnel liner and the unlined tunnel.
The penstock splits off just above the powerhouse to a small water treatment plant that also had to be retooled and updated. In addition, the project team reconstructed the city's fish valve unit, complete with installation of a new 1.7MW turbine/generator, and the constructed and equipped the new 15.9 MW powerhouse that also controls the city's other hydro unit at Green Lake.The scheduling of delivery of all necessary materials became a key part of the project due to its location on an island.
Unlike some remote projects, though, attracting and retaining the workforce over the course of the project was not a significant challenge. The team remained cohesive by promoting team-building, and by offering employees both steady, challenging work, and the availability of decent housing in and around town. A significant local workforce was used in all facets of construction. Local contractors, Southeast Earthmovers, ASRC McGraw Constructors, and Schmolck Mechanical, all played a large role in the project. In addition, many local employees were used by Barnard, NAES Power Contractors and Blue Lake Tunnelers.
The tight knit community supported the expansion project from inception and played a key role throughout the project. When electric rates were raised 35% to pay the US$150M budget, the people of Sitka supported and understood the necessity. With US$50M granted from the Alaska Energy Authority, the remaining US$100M will be paid back directly by ratepayers through a municipal bond. While that is a large sum for a town of Sitka's size, the residents familiar with the area'smore than 254cm of rain each year knew that hydroelectricity was their best bet for reliable, long-term electricity.
The support from the community has been tested but continues to remain high even through brief outages during commissioning and switching their drinking water for three months to a subpar water source. The community has been fully involved in the process of construction, rate structure and budget through updates via multiple sources. One of the most popular updates was the monthly tour of the dam site during construction, which ran each summer of the project's two-year timeline. The 100 spots available on each tour filled in a matter of hours after the sign-up sheets were opened.
As project construction neared completion, the team entered the allotted 65-day generation outage, during which the existing Blue Lake powerhouse shut down, as did the city's access to drinking water taken from Blue Lake. The drinking water was replaced via a temporarytreatment plant the team installed that drew water from Indian River at the northern end of the island. The community was asked to and complied with a request to conserve energy during the generation outage to limit the amount of diesel fuel generation required. The residents' and project team's combined efforts resulted in hardly any diesel use during the outage. While many were not happy about the generation outage, most understood why it was necessary.
Meeting the schedule, staying within budget and remaining upfront with and active within the community led to the success of this project. Everyone in Sitka knows about the Blue Lake Expansion Project and understands its immense importance to their everyday lives. Most will advocate for their community doing the right thing despite the fact that US federal funding is not available for hydro as a renewable energy source. Sitka's Blue Lake Expansion Project is proud to be creating energy independence for Sitka's future.
Christopher Brewton, Sitka Utility Director (Owner)
Dean Orbison, Sitka Project Manager (Owner)
Clifton Stump, Project Manager, Barnard Construction Company, Inc. (Contractor)
Jessica Stockel, Project Assistant, McMillen, LLC (Construction Manager)
Susan Penner, Technical Editor, Barnard Construction Company, Inc.