There’s an island growing in the Sturgeon River. You can see it in the bay across from the city’s cenotaph. Twenty years ago, I remember launching a canoe into clear water at that point.
There’s an island growing in the Sturgeon River.
You can see it in the bay across from the city’s cenotaph. Twenty years ago, I remember launching a canoe into clear water at that point. Now, there’s a cattail-covered mass there, one that’s slowly risen out of the deep like some sort of Albertan Atlantis. A land bridge has sprung up as well, slowly creeping towards it from the sewer outlet on the opposite shore.
These new lands are filling in the Sturgeon, trapping fish in the winter and stopping canoes in the summer. They’re also pretty ugly.
And they’re largely our fault. These new territories are made up almost exclusively of sand that washes off our streets and into the Sturgeon – sand that piles up at each of the 46-odd outfalls the city has along the river.
The 2004 stormwater management master plan flagged this sand as a problem, and called for the construction of 23 oil and grit interceptors to stop the build-up. The city has built two of them so far, and plans to spend up to $2.1 million for two more this year.
After years of delay, is the city finally starting to get a grip on its grit?
A gritty problem
The cause of St. Albert’s grit problem is pretty simple, according to environmental manager Leah Jackson.
“Every year we buy a big pile of sand, and every year we put it on our roads,” she said.
The city dumps roughly 4,000 cubic metres of grit on its streets each year, Jackson estimates, and recovers about 62 per cent of it through street-sweeping, catch-basins and grit interceptors. The rest – about 150 dump-trucks worth – ends up in the Sturgeon.
That’s a lot of sediment for a little river, Jackson continues. The North Saskatchewan gets a lot of grit, she notes, but it also has a lot of flow, and can flush it away. The Sturgeon doesn’t, so the stuff builds up at its outfalls.
The results are big sand bars that make a “bloody mess” in the river, says environmentalist Elke Blodgett.
“You can’t even get a canoe across,” she said.
These bars also stop fish from migrating downstream, which may contribute to winterkill, she said.
The 2004 stormwater plan found that some 16,000 cubic metres of grit built up in the Sturgeon within city limits between 1986 and 2003 – enough to raise flood levels in Big Lake by about 10 centimetres or fill 6.4 Olympic-sized swimming pools. Given that most of the grit was near the city’s outfalls and of the same size as the stuff used on local streets, the report found it “likely” that these sediments came from St. Albert and not communities upstream.
Interception
The city took its first big step against grit in 2003 when it built its first oil and grit interceptor under St. Anne Street. It’s under the big metal plate across from St. Albert Place and the cenotaph, explained utilities manager Dan Rites.
“You could walk right by it and not even know it,” he said.
Crack it open and you’ll see a rusty tomb full of dark water. If you can look past the water, you might see three metal hatches that open onto three big settling chambers, the bottoms of which are about 12 metres below the surface.
Stormwater passes through a diffuser at the end of a pipe and spills through the hatches into the first chamber, Rites says. Once it fills the first one, it pours over a wall into the second. By the time it hits the third chamber, the water has slowed down enough for most of the grit (and the oil sticking to it) to settle out. The water then flows out a second pipe and out the outfall by the cenotaph.
This interceptor cost about $269,000, according to Jackson. The city hasn’t built any more of them, but has had developers commission eight more as they’ve built new areas. Four such interceptors are along Ray Gibbon Drive.
The St. Anne interceptor stops about three truckloads of grit a year, according to Jackson, but can’t stop any salts or chemicals in the water. The $865,000 Butterfield interceptor by the Boudreau Bridge (est. 2007) is supposed to stop those by using vegetated ponds instead of concrete chambers – the theory being that the plants will suck up the contaminants.
Whether it works or not is another question. It’s been flood-damaged two years in a row, and didn’t become fully operational until 2010. While it does trap grit, the city has yet to test it to see if it is actually sucking chemicals out of its stormwater, according to Jackson.
The 2004 stormwater plan called for the creation of 23 St. Anne-style interceptors over 10 years at a cost of $10.4 million. Council sunk that plan in 2006 through budget cuts, and in 2010 created a new plan: seven interceptors over 10 years for $4.3 million.
Most of these will be of the St. Anne type due to space limits, Jackson says. Crews plan to put one in at the north-side outlet near the Perron Street bridge (which services all of Mission) this year and another at the outlet near the BMX park (a region which has had oil spills in the past). Each interceptor will cost between $300,000 to $1.3 million, depending on their sizes.
Prevention
Stopping grit is more than just building interceptors at sewer outlets, Jackson says – it’s also about stopping it from getting to those outlets in the first place.
One way to do that is to sweep it up. The city now has about 23 people and eight to 12 contracted sweeper trucks roaming the city sucking up gravel, said operations supervisor Darrell Symbaluk.
“We’ve got just about every available body on deck right now,” he says, and they’ll be working day and night for about four weeks.
The sweepers recover about half of the grit the city uses each year, Jackson says – about 200 truckloads worth. Dump trucks pile it atop a building-sized hill of grit up by the compost depot for eventual recycling or disposal.
We can also trap it. The city has about 4,400 catch basins in its drainage system, Rites says – one under each of those metal grates you see along the street curbs. These concrete pits act as mini grit-interceptors, slowing the flow of water and trapping a total of about 26 truckloads of grit a year.
And you can also stop it at the source. For example, much of the grit at the outfall by the Children’s Bridge appears to come from Grandin Ravine, which empties into it, according to Jackson. The city’s drainage system is funnelling so much water through the ravine that it’s causing heavy erosion – crews have found a two-foot deep crevasse in one spot. The city is now looking at adding culverts to reduce erosion in the ravine.
The city plans to spend about $9 million on these and other anti-grit measures over the next decade, about $4.3 million of which will go towards interceptors, Jackson said.
Our problem to solve
The city hopes to catch 90 per cent of its grit before it reaches the river by 2020, according to the 2009 environmental master plan. We caught about 86 per cent of it in 2009, Jackson says, but that required near-perfect weather conditions.
Even if we catch all our grit, however, we’ll still have to deal with the century’s worth of stuff already in the Sturgeon. The 2004 stormwater report recommended dredging it for about $500,000, but as local environmentalist Dave Burkhart points out, there’s not much point in doing that unless you can keep the deposits from coming back.
“The fewer times you go into the river, the better,” he said.
The city is looking into dredging, Jackson says, but it’s a complex option, one that would require many permits and possible fish habitat restoration.
We caused this problem, Burkhart says, and we should solve it.
“If we didn’t put sand on the road and didn’t wash it into the river, we wouldn’t have a problem.”
