By Christopher Brewton, Susan Penner, Jessica Stockel and Clifton Stump
|Blue Lake sits 6 miles east of Sitka on the west side of Alaska’s Baranof Island. (Photo by Alaska Crane)|
Planning and foresight allowed the City and Borough of Sitka, Alaska, to take advantage of existing hydroelectric infrastructure to meet the needs of growing electrical demand.
In today’s world, many communities are looking for stable energy sources with reliable generation price tags that are not dependent on world market prices and delivery. If they have water accessible, it is natural to explore the costs and benefits of producing hydropower. So it has been with the City and Borough of Sitka, Alaska, built on the shores of Baranof Island along Alaska’s southeast coastline, one of the rainiest cities in the U.S..
By expanding the Blue Lake hydro plant, Sitka was not only able to reduce its dependence on fossil fuel, but also meet the needs of a growing electrical demand.
History and engineering
Sitka is a stranded island system with no interties or other power sources. Sitka has always been 100% reliant on hydropower supplied by the Blue Lake and Green Lake projects, with a diesel plant used for back up generation.
The City and Borough of Sitka owns two hydroelectric plants: Blue Lake, located along Sawmill Creek and commissioned in 1961, and Green Lake, located along the Pacific Ocean commissioned in 1982. The city’s electric department operates the generation, distribution and transmission from these two plants, supplementing the electricity the hydro plants generate with diesel-powered electric generation when needed.
Diesel generation is only needed under two circumstances: when the single line leading into town from the plants goes down; or when the load is too big for the hydro plants, as it did for one month during the winter before the Blue Lake expansion was built.
In 2006, the city experienced a 7% load increase, followed by a 5% increase in 2007. About half this growth resulted from increased use of electricity for heating, and the other half from expansion of Sitka’s seafood processing industry. Because of the isolated grid in Sitka and the need for more electric generation, the city faced the decision in 2007 to either expand its hydro capacity or begin burning diesel, which must be imported at a significant cost of about $3.3 million per year.
|A view from atop the largest crawler crane in Alaska, the Liebherr LR1600. (Photo by Desiree Brandis)|
After multiple studies, the most feasible, environmentally-friendly and cost-effective solution found was to expand the Blue Lake hydroelectric generation system. The Blue Lake Hydroelectric Project, located just 6 miles out of downtown Sitka, included a submerged intake and three turbine-generator units that provided a total capacity of about 7.5 MW. Fortunately, at the time the facility was built community forefathers anticipated future growth in the area’s development. The 145-foot-tall concrete arch dam they’d constructed at Blue Lake was designed to be raised, though at the time this was expected to be by 23 feet. By 2007, city leaders decided that to serve the community’s electrical needs into the future, engineers would need to push the envelope and raise the dam by more than 23 feet.
|After one year of construction, the original spillway still needed to be utilized. The dam was completed the second year, increasing the height by a maximum allowable 83 feet.|
Design of the Blue Lake Expansion Project was awarded to Hatch Associates Consultants Inc. in 2009. Hatch completed the design development study in April 2010. Following the study’s completion, Hatch performed the geotechnical investigation, equipment procurement and final design. Geotechnical studies and advanced design identified 83 feet as the maximum allowable addition to the dam’s height. During the design phase, elements of the design were reviewed and approved by the board of consultants (BOC) and Federal Energy Regulation Commission (FERC). The BOC is an independent board of private consultants composed of three experienced professionals. The BOC held meetings every three months during design, engineering and construction to fully evaluate the project, mainly focusing on problems that were faced or change orders being considered, and made recommendations based on their experience that were culminated in a report and submitted to the FERC and project staff. These tasks were completed prior to bidding the construction in May 2012.
FERC issued the order amending the operating license for the project on May 30, 2012.
Also in 2012, Boise, Idaho-based McMillen LLC (now McMillen Jacobs Associates) was hired to perform construction management, while Bozeman, Mont.-based Barnard Construction Company Inc. was awarded the $83 million construction contract for the project. During the construction phase, Hatch continued to provide engineering support as requested by McMillen Jacobs.
Aspects of construction
In addition to raising the concrete arch dam by 83 feet — the maximum allowable height due to the canyon features — the project included construction of a new gatehouse and intake structure, a 900-foot-long intake tunnel, a 110-foot-long vertical shaft for the gatehouse, a 415-foot-long adit tunnel, and a 350-foot-long vertical shaft for an underground surge chamber. The penstock, which supplies both the powerhouse and Sitka’s water supply, had to be relined in several critical areas, and about 500 feet was replaced to deliver water to the new powerhouse. The relining was necessary to reinforce the tunnel to accommodate the higher water pressure, and the 500-foot replacement eliminated 50-year-old infrastructure and diverted the water to the new powerhouse location.
Two miles downstream from the dam, a new 15.9-MW powerhouse was constructed adjacent to the existing, operating powerhouse and the city’s small water treatment plant. Also, along the penstock, a fish valve unit required to maintain the flow of Sawmill Creek was overhauled to include a new 1.7-MW turbine-generator unit. To complete the package, the team also constructed a temporary water treatment system.
Critical to the project’s schedule, the city took on the responsibility of procuring the major materials and equipment. In Sitka, everything must arrive by barge via Seattle or Anchorage, so thorough, advanced planning was critical for material and equipment delivery. Understanding that the project construction schedule would be delayed if the contractor began material procurement after contract award, the city accepted the risk of procuring the long-lead material items prior to the construction project going out to bid.
Materials procured by Sitka included: three 5.3-MW Gilkes/Hyundai Ideal turbines and generators and equipment, 8-foot-diameter penstock manufactured by T-Bailey, 69-kV WEG transformers, and Linita fixed-wheel and bulkhead gates and the powerhouse superstructure.
After mobilizing to the site, the construction team hit the ground running. Meticulous planning and scheduling was imperative as well. All equipment and materials were at least two weeks away by barge, whether it was the 45 truckloads that comprised the Liebherr LR/1600 crane or the materials needed to batch the 13,000 cubic yards of concrete the job would require. Other significant logistical challenges included 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 10 feet over five days) or constructing the powerhouse foundation 20 feet below the immediately adjacent Sawmill Creek.
None of the access to work was straightforward at the dam site, located up a winding mountain road 2 miles inland from the existing and new powerhouse sites. The dam had been built into a steep rock canyon, which had been a natural barrier between the existing lake and creek below. The right embankment provided the team’s only access. The steep left abutment was located on undeveloped, inaccessible land.
Consequently, the entire project schedule was built around the operation of three cranes, including the Liebherr LR/1600. Two additional cranes supported the team as well, including a 100-ton crawler crane placed on a barge upstream of the dam and a 150-ton crawler crane co-located on the right embankment to provide additional delivery of personnel and equipment.
|More than 1,000 community members took part in monthly tours of the Blue Lake construction site as part of an award-winning public education initiative.|
One of the first orders of business on the expansion project was to design and erect a 120-foot-tall staircase that left the top of the cliff above the dam on the right embankment and descended mid-way down the original dam’s downstream face. This staircase, designed by Petrochem, was used to allow the crew access to the top of the dam.
Subcontractor Blue Lake Tunnelers (a joint venture of Redpath and Frontier Kemper) completed all the underground excavations. These included a the intake tunnel, shaft for the gate house, adit tunnel, and vertical shaft for an underground surge chamber. All of the underground excavation work, with the exception of final tie-ins, was completed in the first year of construction.
|Gate shaft work progresses behind the temporary submerged intake portal at Blue Lake. (Photo by Derik Olsen, Barnard Construction)|
Southeast Earthmovers completed the surface excavation work for the dam staging area, project access road, intake structure and powerhouse. With the surface and underground excavations nearly completed in June 2014, the team began concrete construction on all areas of the project, including the dam raise, intake tunnel, gate shaft and powerhouse.
Once the cranes and staircase were in place, work on the dam could begin. Because the dam was accessible only from the one side, each day superintendents and foremen had to coordinate the movement of their crews and materials by crane. The left and right abutment contact to rock was raised in 10-foot lifts. Each monolith required about 100 to 150 cubic yards of concrete, meaning the dam alone required 8,000 cubic yards to complete. Constructing a thrust block on the left abutment added another 900 cubic yards of concrete delivered via crane to the opposite side of the canyon, more than 320 feet from the crane pad.
|Blue Lake’s new 15.9 MW powerhouse contains three specially made horizontal turbines and also houses controls for all of Sitka’s other generating assets.|
Working through the winter of late 2013 and early 2014 on the island also demanded thorough pre-planning. In scheduling the work from the outset, the team focused on having the new intake tunnel ready for concrete placement and finish work during the winter. Fluctuating lake levels created limited work windows below the existing high water mark for the new intake structure, tunnel and gate shaft. To complete more work in the first year, the team installed a temporary, 5-foot-thick concrete plug in the intake tunnel. This sealed the 12-foot by 14-foot horseshoe-shaped tunnel, allowing completion of a significant portion of work that was originally scheduled for completion during a very short low-water window in 2014.
Work in and on the water also had to be conducted with precision and care. The City of Sitka draws its potable water through the same intake at Blue Lake, and the penstock forks just before reaching the powerhouse to feed the community’s water delivery system. Water in the lake is some of the purest in the U.S., requiring only minimal treatment.
The existing penstock posed challenges as well. Where the penstock was tunneled, it had to be reinforced, while exposed sections of the 8-foot-diameter pipe could be replaced. The sections in solid rock were reinforced internally. The three existing tunnel portals had steel liners that extended into the unlined portions of the tunnel.
To protect the penstock from increased pressure due to a higher lake level, these liners had to be extended. The liner extension required that the team pull in collapsed pipe sections, use 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 unlined tunnel.
Roughly 500 feet of new penstock was installed to deliver the water from the existing tunnel to the new powerhouse. With the new penstock splitting off just above the powerhouse to the water treatment plant, the team also took on retooling and updating the water treatment system.
Work on the project’s new powerhouse was equally as critical to the community’s energy independence. Roughly 2 miles downstream from the dam, where Sawmill Creek empties into Silver Bay, the concrete structure for the new powerhouse took shape after significant work excavating the sub-structure. ASRC McGraw Constructors installed the steel building and precast panel walls. Once the building’s roof and overhead bridge crane were in place, NAES Power Contractors installed the three 5.3-MW Francis turbines. Electrical and mechanical balance-of-plant construction ramped up as the turbine-generators were installed.
On Aug. 17, 2014, the team entered the allotted 65-day generation outage, during which the existing Blue Lake powerhouse was shut down, as was the city’s access to drinking water from Blue Lake. Water was drawn from a temporary treatment plant installed at the northern end of the island, while the community joined the effort by agreeing to conserve energy to limit the amount of diesel fuel generation required. As a result, the city used very little diesel during the generation outage.
The City of Sitka’s entire generating system operates from the new Blue Lake supervisory control and data acquisition control room. Adhering to diligent planning and showing great determination, the project team, supported by stakeholders, completed the generation outage 14 days ahead of schedule.
Sitka officials acknowledge that they have been in a unique position in raising the height of the dam, inundating another 362 acres along Blue Lake’s shoreline and constructing a new, clean energy powerhouse just inland from the incredibly beautiful Silver Bay, where salmon run, herring school up, bald eagles feast, and humpback whales frolic throughout the year. Like many locations in Alaska, hydro here is fish-friendly due to a natural waterfall that prohibits fish migration to the dam. In addition, through old mining claims, Sitka holds title to property within the West Chichagof-Yakobi Wilderness Area, attractive to the U.S. Forest Service and the environmental community. Negotiations in terms of mitigation, as a result, have been very positive.
|Sen. Lisa Murkowski (third from left) visits Blue Lake Dam in 2014.|
The greatest risk in moving forward with the $142 million project were the rate hikes implemented so the City of Sitka could meets its bond covenants. Sitka had not seen a utility rate increase in 30 years, but rates were raised more than 37% in three tiers over two years.
The increase could have produced a major backlash from the community with the Assembly and community at-large hanging the publicly-owned utility for implementing such a sharp hike. But, through efforts of public education, consumers were informed why the project was so important not only for them, but for their children and their children’s children.
The public was informed through many different outlets, including three videos — one of which earned an honorable mention at the 2010 Anchorage International Film Festival — that were produced by Sitka-based Pundit Productions. A pamphlet created in collaboration with the Sitka Conservation Society won an Excellence in Communication Award from the Northwest Public Power Association, while a website and social media were also used.
The most popular means of keeping the public informed about the project, however, were through monthly construction tours. Each of the spots on the first tour was taken within hours when the first sign-up sheet was opened in 2013, and on a snowy Sunday afternoon that April, a hundred Sitkans piled in to their community hall eagerly awaiting the first Blue Lake Dam Tour.
The buzz around Sitka after the first tour was contagious, and every tour offered was also full in a matter of hours after opening the sign-up sheet. Each tour consisted of a PowerPoint presentation, a tour of the dam site and a look at the new powerhouse.
The format for the public tour was also replicated and offered to local schools in which five separate classes and the entire seventh grade took part. As a special project to explain hydro to younger students, a model was created using rubber tubing, buckets and a wooden spin wheel to replicate the turbines. It was so well received by not only the students but also by the teachers that the model was used on all of the public tours as well.
In all, 10 public tours and about 1,000 of Sitka’s residents have seen the Blue Lake Expansion Project up close on a two-hour educational presentation and tour. Around Sitka, people were excited with their newfound knowledge of the project and it really enabled the project team to do their job effectively and efficiently.
Instead of lamenting the rate increase, something completely different happened, with just one customer complaining — a remarkable achievement. Residents in the small town of Sitka knew, because they were well informed throughout, that the Blue Lake Expansion Project was what was needed to secure their energy future.
The tours and public outreach were created through coordination from the owner and contractor under direction of Jessica Stockel with McMillen Jacobs Associates. McMillen Jacobs Associates was recognized for its work in April 2015 with an Outstanding Stewards of America’s Waters Award from the National Hydropower Association.
The additional hydroelectric power now being generated in Sitka directly decreased the city’s dependence on diesel fuel for power generation. In mid-November 2014, operators fired up three new 5.3-MW turbine/generators and wet-tested another 1.7-MW smaller unit that came on line in March of 2015, resulting in a project that was completed safely, on time and within budget. Blue Lake is now the lead generating station for the city, coordinating power generated by the city’s 16.5-MW Green Lake hydroelectric plant as well. All told, this new system has the capacity to deliver 33% more power through the use of the same water source — enough energy to promote the possibility for local growth.
Christopher Brewton is utility director for the City and Borough of Sitka. Susan Penner is a technical editor for Barnard Construction. Jessica Stockel was a project assistant for McMillen Jacobs Associates. Clifton Stump is a project manager for Barnard Construction.