AUBURN — Cleaning the Twin Cities’ water supply intake pipe is a pretty straightforward job, according to water officials.
“It’s the planning that takes all the effort,” said John Storer, superintendent of the Auburn Water District.
Workers began cleaning the intake pipe Monday and they’d all but finished by Wednesday morning.
There will be one more inspection Thursday, and the $183,000 project should be complete, Water Treatment Manager Michael Broadbent said.
To get there, workers had to build a duplicate intake system to keep the water flowing to the Twin Cities.
“I compare it to heart bypass surgery,” Storer said. “You know you’re going to be working on the heart, but all the effort is getting the blood flowing all around so you can do your work. That’s what we’ve got going here. I don’t want to minimize the cleaning itself, but getting set up is what takes all the effort.”
Lewiston-Auburn’s water is supplied by a single, 48-inch-diameter intake pipe installed in the middle of the lake in 1996. It’s designed to pump water from the center and bottom of the lake, relatively free of winter ice and sediment. The intake is about 900 feet out into the lake away from the shore and about 50 feet below the water’s surface.
The lake had quality issues in 2012 and 2013 after an algae bloom turned up, killing trout. The district was prepared to treat the water with algacide this past summer, but it wasn’t necessary. Storer said lake water quality had returned to normal levels.
A video survey of the intake last fall showed coatings of algae and lake sponges two to three inches deep along the inside of the pipe.
Broadbent said that brown sludge never would have made it into Twin Cities’ taps, but it might have slowed things down considerably. The water system has sensors that shut down the pumps when the water starts getting cloudy or discolored, so any algae that might have sloughed off the pipes would have shut things down.
Storer said it was mostly a concern for high-demand times.
“Our concern is another situation when we had those fires in Lewiston,” Storer said. “There was a big demand for water, so we responded by turning up the pumps.”
Faster water-flows in the intake could dislodge some of that algae, however.
“That flow change can literally pull that material off of the pipe wall, and then we have dirty water,” Storer said. “We have to shut down and flush the system. So now, they are scouring that pipe so we don’t have to worry about it.”
Once the duplicate intake system was ready, Storer said divers went out into the lake and began prepping the main intake pipe. An automatic scrubber, spraying water at up to 1,200 pounds of pressure per square inch, was sent into the pipe to dislodge the algae and sponges. Then, the crud was pumped on to the shore and into dumpsters lined with filter bags.
“The water pressure tears it all up, so it’s more a fine powder,” Broadbent said. “The water coming out of there with that in it looks more like tea than anything else.”
It will be shipped to a landfill, Broadbent said.
It’s the first time the pipe has been cleaned since it was installed. Broadbent said the district will inspect it again in two years to see if it needs cleaning.
“We don’t know what we’ll find,” he said. “We may need to clean it again. We may be able to wait another 20 years before we do it. We’ll have to see what happens.”