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Damn! What a Dam!

SMALL TOWN ENDS THEIR DEPENDENCE ON IMPORTED FUEL BY RAISING THE LOCAL DAM AND ADDING A NEW POWERHOUSE

BY LISA KOPOCHINSKI

If ever a project deserved the recognition of an Alliant Build America Award, it would be the Blue Lake Expansion Project.

Situated in remote Sitka, Alaska, this project shows the fierce determination of one small community (population 9,000) to become energy independent with green energy — something many communities around the world aspire to.

Receiving the Alliant Build America Grand Award — as well as winning the category of Federal and Renovation and a Marvin M. Black Excellence in Partnering Merit Award — the Blue Lake Expansion Project showed how vigilant the residents of the City and Borough of Sitka were to follow in the footsteps of their forefathers. They voted nearly unanimously (97 percent) to end their dependence on imported fuel by raising their local dam and adding a new 15.9 MW powerhouse to the system to produce more hydropower.

“The project was challenging in that it required work in so many disciplines and each area posed logistical and access challenges,” recounts Clif Stump, project manager at Barnard Construction Company, Inc., the general contractor on this complex project and a Montana Contractors Association member. “Community support, though, was phenomenal and community involvement was ever-present.”

Barnard added 83 feet onto the 145-ft-tall, 1950s-era concrete arch dam that had been built into a narrow slot canyon on Baranof Island in Southeast Alaska. This brought the dam to its maximum geotechnical height. The dam impounds the 3.25-mile-long Blue Lake Reservoir from which the area has been drawing most of its power for more than 50 years.

To meet the community’s current and future power needs, Barnard was tasked with constructing a new 15.9 MW, 12,835-sq-ft hydroelectric powerhouse equipped with three 5.3 MW horizontal Francis turbine generators.

“To get the water to the turbines required constructing a 900-linear-foot (LF) new intake tunnel, a new gatehouse and concrete intake structure, which required 120 feet of vertical rock excavation on the shores of Blue Lake,” explains Stump.

In addition, Barnard constructed a 360-vertical-foot (VF), 11-ft-diameter surge shaft. This project also encompassed a 110 VF gate shaft; modifications to an existing tunnel; 414 LF adit tunnel; a new penstock section; addition of two 69kV transformers in the associated switchyard upgrade; installation of a 1.6 MW micro-hydro unit; and installation of a temporary water treatment facility that supplied water to the entire community during a critical phase of the project.

As the power producer and provider for all residents and businesses on Baranof Island, the city had reached the maximum capacity of its two hydroelectric plants, limiting the area’s potential for growth. The Electric Department became reliant on “backup” diesel generators to provide electricity for residents and businesses and had to impose fuel surcharges that increased all customers’ bills. In addition to being one of two hydroelectric power sources, Blue Lake also provides the city of Sitka with its drinking water.

“During construction, despite a significant outage of the Blue Lake supply, the city’s drinking water was never interrupted,” says Stump. “Teamwork and innovation by the project team led us to the solution of installing a temporary microfiltration membrane water treatment plant on an old water source. Our entire team considered this a great accomplishment.”

FAST TRACK SCHEDULE
With a project start date of Nov. 1, 2012, the $92.5-million project was completed on a fast-track schedule under the intense scrutiny of a heavily invested public. The powerhouse was constructed directly adjacent to Sitka’s existing hydroelectric facility that remained in operation throughout the project until the 65-day generation outage when the new facilities were brought online.

Successfully meeting this outage deadline was critical to the city. If the deadline was missed, Sitka would have faced a one-year delay in generation startup and risked having to provide significant supplemental diesel generation until the plant could be commissioned.

“We completed the Generation Outage 14 days early,” says Stump. “In fact, the entire project was completed ahead of schedule on Jan. 30, 2015. With help from Mother Nature, the lake level rose almost immediately and actually spilled over the raised dam more than a year earlier than planners had anticipated.

This meant that the city didn’t have to spend any money on diesel generation in 2015 — a significant cost-saving benefit to area residents in the first year.”

Dismantling the scaffolding walkway on top of the old spillway and beneath the new dam as the project wraps up.

Dismantling the scaffolding walkway on top of the old spillway and beneath the new dam as the project wraps up.

SIGNIFICANT CHALLENGES OVERCOME
While this project was a huge success, it was not without its significant challenges related to schedule, safety, powerhouse location, access and weather.

The dam is located in one of the rainiest locations in the U.S. where more than 100 inches of rainfall annually is not unusual, and with heavy winds that can often exceed 60 mph. Adding to the challenges was the fact that the only access to the dam was a narrow dirt road along a steep canyon to an area above the right abutment.

Getting manpower and materials to the dam required ingenuity.

“Although the team engineered a scaffolding stairway that wrapped over and down a canyon wall, the scaffolding’s use was limited to initial work and observation,” explains Stump. “The stairway couldn’t be used for material or equipment delivery or for access to the left abutment.”

To address access needs, a Liebherr 1600/2 crane — the largest operating in Alaska at the time — served as the workhorse of the dam construction. However, just getting it to the site required approximately 40 truckloads up the mountain road before it could be assembled on location.

“The wind and rain played a significant role in how we constructed the project and affected our crews,” Stump recalls. “Each person working on the dam carried a 30-lb. tool belt while wearing a fall protection harness anchored 200 feet above the ground.

And it affected our schedule. Wind gusts limited our ability to move crews and materials onto the project. In fact, wind caused more schedule interruption than rain due to the team’s reliance on the cranes.”

Seasonal lake level fluctuations were the main schedule driver for the dam work. These fluctuations occurred rapidly on occasion following exceptional rainstorms.

With respect to the new powerhouse, it had to be constructed in tight quarters and in hard rock next to the island’s existing power plant, which was to remain operational until a single generation outage when the new powerhouse could be brought online. In constructing the powerhouse the team also had to be mindful of the salmon spawning in the immediately adjacent stream, as well as the eagles and bears that continued to feed on the salmon near the jobsite throughout the two years of construction.

“This island location required a cohesive team that could agree to significant upfront planning for all material deliveries,” says Stump. “All major materials had to be delivered to the project via barge, which meant placing orders with plenty of lead time to ensure the team could maintain the schedule. Seasonal lake level changes also limited work windows on the dam and intake structure.”

Ensuring safety on such a multi-faceted project required strict attention to detail every day by every person involved, given the limited workspace and access on the dam, the fall hazards associated with working on a dam up to 230 feet above the ground, and the fact that all materials were being delivered overhead by crane.

The team kicked off the project by developing a project specific Health and Safety Plan that incorporated the unique requirements of the site, the specifications, and the city of Sitka’s practices. The team incorporated specific safety-related discussion in a series of regularly held meetings.

As a result, there were no serious injuries on this project.

COLLABORATIVE APPROACH
Ultimately, collaboration led to the success of the project. The challenges the Blue Lake team overcame can largely be attributed to the strong collaborative approach that emphasized excellent planning and open community — from project kickoff through completion.

The team also was successful in managing impacts on the local community. With residents so vested in this project, it was critical to keep the community involved and maintain a positive image. A great deal of effort was invested in keeping residents up to date, including monthly presentations in town, dam tours open to the public, countless private tours with schools and local officials, and a dedicated Facebook page.

“The end result was a high-quality project completed ahead of schedule and within budget, both of which speak to a successful project for all parties involved,” adds Stump.