Removing a large water intake and concrete pier poses environmental challenges

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hydrodemolition
A spreader bar and additional tower sections maximized the hydrodemolition robot’s reach.

By Arielle Windham

Located more than 700 km north of Winnipeg, the Keeyask Generation Project is being constructed on the lower Nelson River. This 695-megawatt hydroelectric generating station, scheduled for completion in 2021, will be a source of renewable energy, producing an average of 4,400 gigawatt hours of electricity each year.

The energy produced will be integrated into Manitoba Hydro’s electric system for use in the province and to export to other jurisdictions. Now in its seventh year, the project has managed a number of location-specific challenges.

One such challenge occurred in 2017 when water in a 60 cm pipe in the intake froze, damaging a 2.5 metre thick concrete pier. To minimize impact to the overall project, Keeyask managers opted to use hydrodemolition to remove the damaged section. The job required a specialized contractor able to overcome environmental and logistical challenges, while delivering quality results.

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Water Blasting & Vacuum Services Inc. (WB&VS), a Canadian industrial cleaning specialist, secured the contract based on a plan that provided not only the efficiency to complete the 140 m3 removal work on time, but recycled nearly 80% of the water.

“This was a very intriguing project and the first of its kind,” said Maurice Lavoie, general manager at WB&VS and site manager for the project. “The pier was solid concrete, 2.5 metres feet thick, 12.2 metres wide and 9.1 metres tall at the highest point. A portion of the structure needed to be removed and re-poured. No one in Canada had used hydrodemolition to vertically remove 2.5 metre thick concrete.”

Location was another key challenge. The construction site was approximately 4,000 km from the contractor’s headquarters in Edmundston, New Brunswick, and over 700 km north of Winnipeg. Limited access needed to be carefully factored into any proposed solution.

While project managers could provide access to water, power or other general construction supplies, getting specialty equipment or replacement parts presented a time-consuming challenge. Contractors needed dependable equipment and a fully stocked toolbox to limit any unnecessary downtime.

“The project had a lot of challenges to overcome,” Lavoie said. “The remote location left us with no access to technicians or spare parts if something were to go wrong. On top of that, we would be dealing with subzero temperatures.” Strict environmental controls also limited contractors’ application choices.

The project partners, known as the Keeyask Hydropower Limited Partnership, which includes four Manitoba First Nations and Manitoba Hydro, had made environmental protection a cornerstone of the overall project. Therefore, while the original brief specified hydrodemolition as an acceptable process, the contractors would need to ensure all wastewater was properly collected and treated.

“Whatever technique we used, we had to ensure there would be no negative impact on the surrounding environment,” Lavoie said. “Limiting environmental impact is always an important part of any project for our company, but, when combined with this project’s remote location, we knew there would be additional challenges. From previous experience on a job site at the Muskrat Falls Generating Project in Labrador, we knew hauling water in and out was an option, but it was costly and inefficient. Treating the water on site and reusing it was the most economical and environmentally friendly solution. With the Aquajet EcoClear we already had the right machine to make it work.”

Clear solution

The EcoClear water filtration system allowed the contractor to present a solution to project managers that promised maximum productivity, while minimizing resource consumption and protecting the environment.

WB&VS purchased the EcoClear system in 2017 as a more efficient and cost-effective alternative to hauling wastewater with vacuum trucks for off-site treatment. The system neutralizes water pH and reduces turbidity to allow safe release back into the environment. It has the capacity to move up to 20 m3 per hour.

However, for the hydroelectric power project, rather than treating and releasing the water, WB&VS proposed using the EcoClear system as part of a closed loop system that would recycle the water back to its Aqua Cutter 710V.

It would be the company’s first time using the EcoClear to recycle water on such a large scale, but Lavoie and his team were confident the EcoClear and 710V would make the perfect pair to tackle the challenging application.

Clearing a path

The WB&VS team arrived at the jobsite in March 2018. With temperatures averaging -29°C and dipping as low as -40°C at times, a hoarding system and heaters had to be set up around the demolition site to provide shelter and keep the pumps operating.

An average of 4 m3 of concrete was removed and an estimated 151 m3 of water was used in a 12 hour shift.

In addition to the EcoClear system and 710V, the contractor used a spreader bar and additional tower sections to maximize the hydrodemolition robot’s reach. An extension kit allowed the contractor to make a 4 m wide cut, as well. These enhancements greatly reduced the downtime frequent repositioning would have required. Additionally, WB&VS employed additional lance sections to increase efficiency and allow the depth the project required.

Steve Ouellette, lead supervisor at WB&VS, was put in charge of the closed loop system with two 80 m3 tanks providing water to the Aqua Cutter 710V. Wastewater was directed to a low point, then pumped to the EcoClear. Once the water was treated, it was pumped back to the holding tanks for reuse. An average of 4 m3 of concrete was removed and an estimated 151 m3 of water was used in a 12 hour shift.

Of this, roughly 20% of the water was lost during the hydrodemolition process due to evaporation and absorption into the concrete. However, the EcoClear system was able to collect and recycle the remaining 80%. Over the course of the project, the EcoClear processed almost 5,000 m3 of water.

WB&VS worked with project managers to integrate demolition into the complex timeline of the overall project, completing the work in two multi-week phases. Lavoie and his team operated the Aqua Cutter daily for almost an entire 12-hour shift, working in 4 m wide sections to completely demolish the wall. A separate crew would come on at night to remove rebar and debris.

The process repeated for approximately 41 days of blasting and a total of 53 days on site. Demolition was finished by May 2018.

For more information visit www.waterblastinginc.ca.

Read the full article in ES&E Magazine’s August/September 2020 issue:

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