Recent update on York Region’s Sinkhole Mitigation Project (20-102) – currently happening on Yonge Street south of Henderson Drive, in the Town of Aurora. The update was presented to members of Council during the January 26, 2021 Aurora Council meeting.
Presentation started at 00:04:05 by Mark Nykoluk, Senior Project Manager, Capital Planning and Delivery, York Region Transportation Services.
The purpose of this presentation was to provide information on the current regional project. On Yonge Street, south of Henderson Drive there is a dip in the road where the rail corridor crosses over Yonge Street. The rail corridor is the Barrie GO line. To the south of the project is Industrial Parkway South and to the north of the project is the Metro Plaza.
This is a unique site with a very high groundwater table along with the surface water that collects at the dip in the road. Before construction started in the spring 2020 there was a visible natural dip in the road. So between the high ground water table and the dip in the road where the surface water collects, the project is a bit like fixing a leaky bathtub when the bathtub is still filled with water. And because of the water collecting at this location sinkholes have been forming here for over decades. At 00:05:57 Mr. Nykoluk showed photos of an emergency repair in 2016.
The current fix is reconstructing and expanding an infiltration gallery under Yonge Street with a series of underground pipes with holes in them to whisk away the underground water. There is no road widening as part of this project.
At 00:06:33 the top picture (bird’s eye view) shows the infiltration gallery apparatus under the road where the blue lines are the pipes with holes in them that once built will whisk the water away from under the road to reduce the formation of sinkholes. The water collected in the blue pipes will flow by gravity into the adjacent storm sewers and then into Tannery Creek.
At 00:06:56 the bottom picture (side view) shows the road and the red is Yonge Street dipping under the rail corridor.
The final design will consist of underground pipes with the holes in them and will be buried below with a layer of sand, then a layer of concrete, and finally a layer of asphalt.
The project was awarded in the spring of 2020 and was planned to be completed by the end of 2020. Two permits were required from the Ministry of the Environment Conservation and Parks (MECP). One permit to draw down the water so the work can be done in a dry environment, like draining part of the bathtub. A second permit was to add and rebuild the pipes.
The existing rail bridge above Yonge Street in that area will be twinned by Metrolinx in their upcoming project scheduled to begin in the spring of 2022. Therefore, there is a need for the York Region project to be finished before the end of 2021.
The work began with site preparation and the closing of the southbound lanes on Yonge Street. To drain part of the bathtub the water was pumped out of the ground using wells allowing working in a dry setting. The pumped water goes through collection tanks before it is released into Tannery Creek. Water can’t be pumped too much too quickly not to disturb the footings of the existing rail overpass bridge.
Shortly after the work began in spring 2020 it was discovered that the underground conditions were not as expected; therefore, one of the permits needed a revision. With the Covid situation this permit revision took a bit longer than typical but did arrive in the fall of 2020 which allowed the work to continue.
Once the work resumed however, another challenge arose. The contractor wasn’t able to draw down enough water to work in the dry. As a result, more de-watering wells were installed. Additional wells have been installed down the centre of Yonge Street. Pumping has now resumed and is planned to continue during the winter months to minimize project duration and impacts to pedestrians, cyclists and the travelling public.
York Region is concerned with Yonge Street lane restrictions and its impact on the travelling public. If more water needs to be drawn down than presently allowed the second permit needs to be revised again and that could take time. However, this was factored into the decision making process since the project needs to be completed in 2021 to make room for Metrolinx’s new bridge coming in 2022. The target end date is fall 2021.
Council Comments and Questions to the Presenter
“What confidence do you have that this is the one that will fix this problem?”
Cllr Gallo (at 00:10:46) said that in his 25 year history in the Town this is not the first time this repair is happening. “What confidence do you have that this is the one that will fix this problem?” Mr. Nykoluk said that York Region had been working on this project for a couple of years and believes that the current solution is the right solution. There is an existing infiltration gallery underneath Yonge Street and if that wasn’t functioning then water would actually be over topping Yonge Street right now. The selected solution is to rebuild and expand that infiltration gallery similar to the other infiltration galleries that have been designed and built in the Region.
“We found zinc in the water that wasn’t there in any of the testing before.”
Cllr Gaertner (at 00:12:11) asked about the current infiltration gallery under Yonge Street. Mr. Nykoluk replied that there is an existing infiltration gallery. Added that a more recent York Region infiltration gallery was built on Bayview Avenue between Elgin Mills and just north of 19th Avenue and that design and build won the North American Project of the Year Award. A very well recognized project and York Region is bringing that expertise to this project.
Cllr Gaertner, further asked about the contractor discovering that the site conditions were not as expected based on the pre-construction testing. She recommended finding another contractor. “How could this not have been known? We all know there is water under there; we all know it’s a challenge. This is the third time since I’ve been here that I can remember. How is that possible that we just went so badly wrong?” Mr. Nykoluk replied that nothing went wrong. “What happened was that we installed one well to check the composition of the water and to calculate the quantity; and it was during the construction that the composition of the water was different than what we had determined during our design. And when there’s a high ground water table sometimes it’s a little difficult to put a lot of wells into the ground. But we did do a number of geotechnical boreholes for instance. We looked at the composition of the soils, but it was actually the water itself which caused us a bit of a problem. We found zinc in the water that wasn’t there in any of the testing before and it was through the MECP that we worked with closely and they determined that we could proceed with the project but we needed to revise the permit.“ He further elaborated that it wasn’t the contractor or the work that was done beforehand. It was the unexpected composition of the water never experienced before.
Cllr Gaertner (at 00:16:44) asked for an explanation why zinc in the water caused a problem. Mr. Nykoluk replied that in order to extract the water out of the ground a permit is required from the ministry; and then to dispose that water in a proper way a discharge permit from the ministry is required to either discharge that water into the sanitary sewer or storm sewer. York Region elected for this water to go into the storm sewer based on the capacity of the storm sewer and the previous testing that didn’t indicate any of this material (zinc). However the amounts of zinc in the water didn’t meet the Region’s sewer discharge by-laws based on province-wide standards. Therefore approval from the MECP was required to revise the permit to allow this level of zinc into the groundwater.
“Contractor set up the de-watering system based on their understanding of the contract and presently the contractor did not achieve the drawdown that was required.”
Cllr Gilliland (at 00:18:26) asked questions along the same lines as Cllr Gaertner, more related to permits. Mr. Nykoluk replied, again MECP allowed York Region to extract the water to empty out the bathtub so work can be done in the dry. The second permit had to do with the actual building of the pipes. When the contractor bids on the project York Region asks them for a final product and not how they are going to deliver the product. So the contractor set up the de-watering system based on their understanding of the contract and presently the contractor did not achieve the drawdown that was required. Through dealing with the contractor more wells were inserted in attempt to draw the water down. Now with the high ground water table it is not advisable to put too many wells in the ground or it will turn into a bit of Swiss cheese. So the contractors experience so far is indicating a ground conductivity of a certain way, and York Region’s detail design understood the ground conductivity in a slightly different way. The permit is based on the detail design and if the water conductivity is slightly different because water underground is “doing all sorts of crazy things, it’s up to the mother nature,” York Region may have to go back to the MECP to ask to pump out a bit more water; and thus another permit revision.
Cllr Gilliland (at 00:21:28) said that it is unfortunate that this contractor perhaps didn’t fully understand the entire context of the area. Said, in her opinion, that area is going to get worse especially in spring when snows melts can cause flooding and the high water table. Then she added, “help me understand what is the worst case scenario and the preparations we have in place because I am not fully confident that we’re not going to need to go back to pump more water and I feel like that’s going to end up happening again just based on what I’m hearing? Shed some light on what those backup plans are?” Mr. Nykoluk (at 00:22:41) said that the surface water really isn’t the problem. It is the underground water that is causing issues and that’s what York Region is trying to fix through the detail design process and that shouldn’t change in the spring. What is flowing underneath should be pretty similar to what we’ve experienced so far. Dealings with MECP in between were built into the timeline. He also said that the project is not very big, it is only about 120 meters by 20 meters; and there is no road widening. Design calls for opening and rebuilding the current infiltration gallery. It took a lot of effort and design to understand the underground water characteristics. The composition of the water was unexpected. Furthermore, Mr. Nykoluk concluded, “we are confident that when the contractor gets down to the level that he needs to, they need to work in the dry; we’re confident that this project will be a success.” Cllr Gilliland asked, “If we were not successful in these next steps and it just did not work and it was one of those we just did not foresee that challenge, what would that challenge be?” Mr. Nykoluk replied, “That’s a very good question” and further elaborated that part of the work in the area includes a structural design of the road. The road will be monitored for the amount of passive water that’s been coming out of the site’s infiltration galleries. A cement slab will be installed underneath the asphalt to provide some additional support. He added “we’re planning for success and we’re confident that this will work, based on our previous award-winning projects.”
“I would always encourage the Region to continue to improve the lines of communication.”
Cllr Thompson (at 00:25:26) commented, “I would always encourage the Region to continue to improve the lines of communication with us and provide explanations because inevitably you’re here because we had a lot of questions and we didn’t have a lot of answers … if we can improve the lines of communication between the Town and the Region and the Region and Council as well, I think that only helps serve the residents better and gets the information out sooner rather than later.” Mr. Nykoluk agreed.
Earlier in the presentation Mr. Nykoluk said, “May I take this opportunity to thank Aurora’s staff, particularly the engineering department, very knowledgeable, helpful, and a pleasure to work with.”
Cllr Kim askes for confidence levels on finishing this project on time in fall 2021.
Cllr Kim (at 00:27:00) on the same topic touched on the lines of communication. Also he asked for confidence levels on finishing this project on time in fall 2021? Mr. Nykoluk, replied “we are very confident and again the project is not very big; we just got to get it off the ground and we are getting off the ground now. We normally create our contracts on what’s called working days. There are 20 working days in summer time. We don’t include weekends. It depends on the rain; rain will turn a working day into a non-working day. But there is only in total 120 working days in this project and lot of that had to do with setting up the monitoring equipment for settlement. We are very concerned about settling at the Metrolinx rail structure for instance. So a lot of the prep work, settlement monitoring the ground water management plan, the setting up of the wells – that’s all part of the 120 working days. So right now, we probably only have about 80 working days of work to do, which is about four months’ worth of work.” The contractors are on site and the pumping is happening. “We are also liaising very closely with Metrolinx and we understand their urgency in the double tracking that’s going to be happening next year, so it is imperative that we get this job done this year.”
“Is there any chance of putting up a temporary left turn lane?”
Cllr Kim followed up if Covid was causing issues with this project. Mr. Nykoluk (at 00:30:09) stated there was very little impact on this project or many other York Region projects currently active. Cllr Kim also asked “is there any chance of putting up a temporary left turn lane or is it because it’s such a narrow space there’s really no space for left turn.” Not a chance. Mr. Nykoluk stated that the problem is the complexity of the job. Installing wells down the center of the road actually means a protected area is needed of about a meter and a half between barriers. That complicates things a lot but also reduces the spacing for the vehicles to travel through.
Cllr Humfryes (at 00:34:44) asked to improve the communication lines. She also commented that having lighter traffic because of Covid helps the project. Said that there is a different approach this time and asked about the concrete slab being added to the project, and if that was ever tried before. Mr. Nykoluk answered, “Yes we have, and the Region has addressed this a couple of times and we found some hunks of concrete already in that, I think we even found a freezer, no I’m kidding, there’s all sorts of things, slabs.”
Cllr Gaertner (at 00:36:02) clarified that residents in the area have received communication and the communication can be improved with Members of Council so “we might really be on the inside of this.”
Mayor Mrakas (at 00:37:49) concluded with one question, “Was there any concerns that this had to get done to make sure that the road would be able to carry the capacity of the double track that’s going in?” The answer was – no concern with double tracking.
And that was the sinkhole Yonge Street project update as of January 26, 2021. In conclusion, it would be interesting to find out where the zinc came from in the underground water, especially when it was never found there before.