Inside Yellowknife's new $30M water treatment plant
Added filtration may make spring boil water advisories a thing of the past
On Monday the City of Yellowknife offered the first tour of its new $30-million water treatment plant.
The plant opened quietly in June, ending a 32-day boil water advisory. It is expected to make such advisories a thing of the past, because it does more than just chlorinate water; it also filters out dirt and debris.
Where does the city's water come from?
Yellowknife's drinking water comes from Yellowknife River. It's transported to the city via an aging, eight-kilometre underwater pipeline. The line — inspected every two years by divers — begins about 1.5 kilometres from the bridge crossing Yellowknife River, proceeds past islands like Jolliffe Island, and terminates at the plant.
Once at the plant, the water is initially filtered through a strainer that looks a bit like a Dalek robot from Doctor Who.
Then the water proceeds to a series of tan-coloured pipes, each equipped with a membrane filter at the bottom.
Each membrane filter is in turn made up of hundreds of densely-packed strands resembling bundles of dry spaghetti. Dirt and debris accumulate on the outside of each strand; clean water is pushed out through a thin, barely noticeable hole in the centre.
Goodbye chlorine gas, hello sodium hypochlorite
A lengthy boil water advisory in May was issued because of turbidity — cloudiness due to particles suspended in the water. Turbidity is measured using Nephelometric Turbidity Units (NTUs). In May, Yellowknife's drinking water hovered between 8 and 9 NTUs. (During a 2003 advisory, it was 50 NTUs.)
In the new treatment plant, after the water is filtered — but before it gets chlorinated and eventually makes its way to your kitchen tap — the turbidity level of the water is measured. The plant aims for a level of 0.1 NTUs before chlorination.
The way the city chlorinates water has changed, too.
"Previously we used chlorine gas, which is a much more dangerous chemical and required more stringent safety protocols," says Scot Gillard, the city's water and sewer superintendent.
"Chlorine gas is basically 100 per cent chlorine, so it kills you if you make a mistake."
The new solution used is sodium hypochlorite, which Gillard says is "10 times weaker than a store-bought bleach."
The new plant's up and running. Now what?
Now that the water treatment plant is complete, the city is turning its focus to the other crucial piece of its water system: the pipeline feeding water from Yellowknife River.
The line was installed in the 1960s.
"From sediment over the path, there's always stresses on the joints of the pipe," says Gillard.
"There is the potential over time, given frost movements over the surface, that that pipe could separate and fail."
Replacing the line could cost around $20 million, estimates Chris Greencorn, Yellowknife's director of public works and engineering. A previous estimate from a few years ago pegged the cost at $10 million.
But the city does have another option: drawing water from Yellowknife Bay and spending between $4 million and $5 million on the equipment needed to treat that water for arsenic.
City council will ultimately choose between the two options.
"Because of pressures and the location of Giant [Mine] and the tailings ponds, the public perception has always been to keep it at the river, because...if there was a release from Giant, at least our water source is still upstream," says Greencorn.
Greencorn says the pipeline may need replacing by 2020.
"We're approaching the end of its useful life. But if it continues to serve its purpose, we're not just going to replace it haphazardly. We'll plan it properly in the capital budget."