Engineering firm shares options for YK’s new water pipe route
On Wednesday evening, engineering firm AECOM presented the two route options being considered for replacing the 8.5 km steel pipe that supplies drinking water to Yellowknife.
Under both options, water will continue to be drawn from the Yellowknife River, though the route it take to get to the city’s water treatment plant varies.
Option A (the teal line in the below image) follows a very similar path to the existing water main, with slight variations due to a better understanding today of which areas of the lakebed are the most stable and suitable.
Option B (the pink line in the below image) would see water pulled out of the Yellowknife River and along the Pumphouse #2 Road, then down Highway 4 for approximately 500 metres before entering Yellowknife Bay.
Option A and B meet near Hideaway Island and follow the same route – called the “common alignment” – back to Pumphouse #1 off of School Draw Avenue by the city’s water treatment plant.
Both options have their pros and cons, and a decision has not yet been made as to which one will be selected. AECOM’s next step is to deliver a draft preliminary engineering design report to the city later this month, which will lay out the options in greater detail and include the consultant’s recommendation.
Updated costs are being worked on right now and will also be included in the report.
The city is expected to review the options and come to a decision in the new year.
So what exactly are the options?
Jay Allen, a civil engineer with AECOM, explained that Option A would involve dredging to lay the pipeline in the shallow part of Yellowknife Bay near the mouth of the river to ensure the pipe is in deep enough water that it doesn’t freeze. This isn’t the preferred option, as it would stir up lots of sediment.
If Option B is selected, construction of the route under the lake would be completed through horizontal directional drilling. This means a hole would be drilled under the sediment and rock at the bottom of the lake, and then the pipe would be inserted. It would take about six months to drill the section between the north end of Yellowknife Bay and Hideaway Island.
This drilling will also be done at all shorelines, no matter the option chosen, as it’s the best way to protect the shore.
Meanhile, common alignment path between Hideaway Island and Yellowknife was identified as the route with the least amount of underwater obstacles and risk of accidents, such as being hit by a boat anchor.
The common alignment section can be completed in the summer or the winter, as over this section the pipe will be filed with water at the surface and then slowly sunk to the bottom of the lake. There are also pros and cons to getting the work done in each season, such as impacts to summer boat traffic or the Dettah ice road; the ease of dredging in each season, the ice thickness to cut through or hold equipment if completed in the winter; and the availability of barges to help in the summer.
All alignment options are also careful not to cross over the existing water pipe, which will remain operational while construction on the new water supply pipe is completed. After construction, the old steel pipe will be left in place to limit disturbances to the bottom of the lake.
The engineers and the city are leaning toward Option B, but are waiting until they have all of the information to make a decision.
Ryan King, a project engineer with AECOM, said the engineering side is “not just nuts and bolts,” but is also about what is most beneficial to the public and to the environment.
“Going in the river has a lot working against it, which is why we developed Option B,” he said. Having to route the pipe under the Yellowknife River Bridge and through the shallower waters at the mouth of river would be more difficult today than it was 50 years ago due to more stringent environmental regulations now in place.
Chris Greencorn, the city’s director of public works, said the city was “leaning toward Option B, but hasn’t made a final decision yet.”
The route isn’t the only decision to be made. AECOM and the city also have to decide on the pipe’s material. They could go with high-density polyethylene, a proven submarine pipeline material that doesn’t corrode, but needs to be weighted down by concrete bricks; or they could select coated steel, which does corrode after time but is proven to work in Yellowknife as it’s the material the current pipe is made of.
The city is also planning to update the pumphouses, as the existing buildings are quite old and need replacement parts, as well as updating the water intake screens on the primary and emergency water supply pipes to ensure fish won’t be harmed as the pipes pull in water.
What will this cost? When will the work be done?
Yellowknife has drawn its water from the Yellowknife River since 1969. A 2017 study, also by AECOM, recommended the 50-year-old pipeline be replaced in order to continue to meet the city’s water needs for years to come. The river was selected over Yellowknife Bay as the bay location carries some risk due to its proximity to former mines.
The project, which was estimated to cost $34 million in 2019, includes collecting data to understand the best option; installing groundwater monitoring wells, the new pipeline, and intake screens; decommissioning the current pipeline; and upgrading the two pumphouses and pump systems.
A large part of the cost will be funded by the federal government, which award the city $25.8 million in 2019 through its disaster mitigation and adaptation fund for the actual project work. The city then factored in an additional $8.2 million for contingencies and engineering costs.
If updated project costs are higher than projected, the city will be need to find a way to cover them. City administration is currently looking to see if other federal funding pots can help cover expenses above the $25.8 million already received.
The city plans to apply for an amendment to its water licence application in February 2023, which could take until November 2023 to be approved. The amendment would allow the city proceed with the option it selects and to draw water from the emergency intake pipe near Pumphouse #1 during some phases of construction.
Construction is projected to begin in 2024 with some upgrades to the pumphouses taking place, followed by the water line being constructed that winter or in the summer of 2025. Water supply testing will take place in the fall of 2025, and the final upgrades to Pumphouse #1 will be done in the winter of 2026.
The City of Yellowknife is inviting anyone with feedback or questions about the project to submit them through PlaceSpeak.