The City of Nelson will deploy a remotely operated vehicle (ROV) in the Kootenay River on Wednesday to try to locate a leak in its wastewater force main.
The city issued a notice Tuesday saying it had identified two leaks in the Grohman Narrows wastewater force main – one found late last week and repaired, but a second revealed itself Monday afternoon.
Community planning manager Chris Johnson told councillors at this week’s council meeting that the first leak was hard to find.
“We were having troubles locating the leak with the ROV, so divers came in and found it was actually underneath the pipe, embedded in silt,” said Johnson.
Crews were eventually able to access it, though it was located in a challenging spot on the force main, which is held down by large, concrete saddle anchors.
“Imagine a big U-shaped horseshoe thing that goes over top of it. It was right underneath that anchor where we needed to place the clamp,” Johnson explained.
He said the city had to bring in a barge from up the lake to lift the anchor and move it down a few metres so a steel collar clamp could be placed around the pipe and bolted down.
The work was finished on the weekend, but unfortunately another leak revealed itself a few days later, and it too has been challenging to locate and plan repairs.
“We have another leak that we’re currently looking for. But one of the great challenges is getting divers in who are able to come and dive the line. They have their work lined up for the season, so that’s one of the big challenges we have right now,” said Johnson.
He said an ROV will be deployed Wednesday to swim the line again to try to find the leak. Once the city secures a dive team, repairs will follow.
He added that all the leaks on the force main seem to be coming just downstream from the field welds, which the city believes has resulted in debris wearing away the pipe material.
“When the pipe went in, it was welded together in the field, and that weld bead on the inside created a little bump, which just allows for a bit of a back eddy behind it, where we imagine pebbles and things like that are just churning and chewing away at the material of the pipe there, so we end up with all these sort of loonie- or toonie-sized holes in there,” he said.
Johnson also noted that most of the leaks identified in recent years have occurred in either the spring or fall, which he said is a bit of an anomaly.
“It’s a bit of a head-scratcher, and we’re working hard to try to understand what could be resulting in these leaks coming during only a couple of months a year,” he said.
Testing is conducted regularly downstream of the wastewater treatment plant, but Johnson said when a leak is identified, the city increases testing, and so far results have remained within legal parameters.
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