An enormous concrete pump truck pours footings at the new Blue Lake powerhouse. The rig can place 500 yards a day. (Blue Lake Expansion Project photo)
Dean Orbison, project manager for the Sitka Electric Department, updated the Sitka Chamber of Commerce this week on the progress of the city’s largest-ever public works undertaking.
There are three main components to the Blue Lake project: the dam itself, a new intake tunnel and vertical shaft called a “surge chamber,” and the powerhouse.
Residents who drive out the road to the Herring Cove trailhead can’t miss the work on the powerhouse. The hole for the foundation is pretty deep and — so far, Orbison says — dry.
“All these white sacks out here are a cofferdam with plastic over the top of them to keep Sawmill Creek from running into the foundation. The elevation of Sawmill Creek is about twelve feet above sea level. The bottom elevation of the foundations and the draft tubes — the part we’ve been working on — is at minus twelve. If Sawmill Creek were to leak in there, it would be a wet mess.”
Orbison reported to the Sitka Chamber of Commerce at the start of this project. Midway through the $140-million effort, his enthusiasm has not tapered at all.
He showed a slide of the 660-ton crane — the largest in Alaska — slinging an 8-yard bucket of concrete over forms erected on top of the existing dam. The crane used to be fun to talk about, but now it’s already old news as the next piece of super-equipment has arrived. It’s a concrete pump truck, like you might see pouring the foundations of a skyscraper in a city.
“The crane is cool up at the dam. This pump truck here, they load it with two concrete trucks. And they can sit with that pump truck there and pump concrete to any location in the powerhouse. This snout, you just put it over where you want it, turn on the pump, feeding the concrete in there with two trucks at a time. That truck showed up one morning, the first day of the pour, and it pumped 500 yards in one day. On the very first day here. When they said they could do this I said, You gotta be kidding. They did it. It’s just really great.”
Follow the Blue Lake Expansion Project on Facebook.
The powerhouse is being built by the Arctic Slope Regional Corporation, which recently bought out McGraw Construction. ASRC is one of about a dozen contractors and subs working on the project. Orbison said the city, however, purchased its own generation and switching equipment directly. Most is on site, and all except the new turbines are being stored inside at Sawmill Cove. The turbines themselves, he said, are too heavy to bring inside.
The Blue Lake Dam was originally designed to be raised — about 23 feet. Orbison said Sitka is “pushing the envelope” by going up another 83 feet. The canyon walls are so steep that the appearance of the lake won’t be affected much by the increase in water level. At the back of the lake, though, 362 acres of the inlet valley will be inundated. Orbison said the state Department of Environmental Conservation put the brakes on plans to salvage the timber, to protect the quality of Sitka’s drinking water.
“Our problem will be floating debris. We’re not logging the back of the lake because DEC didn’t want us taking any chances at contaminating the drinking water and they said we’d rather you didn’t log it. Because as you log it you’re going to walk around on the ground and tear it up and make mud and so forth. So we said okay, we won’t log it. By not logging it, we’ll end up with all sorts of floating debris in the lake. What we’ll do is gather it up when the lake level’s up and haul it down to this area here and when the water level goes down, we’ll go in there and burn it. And when the water level comes up, we’ll go in there and get another bunch and put it in there. The idea is to keep all the debris at this end (the far end) of the lake, and we’ll have another debris boom at this end of the lake (the near end) protecting the part that we drink.”
Orbison reported no major delays in the project. Some pleasant surprises were the quality of the rock in the new intake tunnel, and where the dam meets the canyon wall.
Orbison also pointed out that what made Blue Lake and excellent place for a hydro project, also made it very dangerous. But he said there were no major injuries since a trackhoe flipped at the beginning of work last winter.
Blue Lake should be completed by February, 2015.
