Friday, March 06, 2009

Another Sewer For the Don

New sewer outlet near mouth of East Don

Travelling in the lower Don is tough in early spring. The paths are lined with frozen mush so it is hard to walk or bike. But I managed anyways yesterday given some unusual mild weather. My goal was to see for myself some recent work being done in the valley. And I was not disappointed. Just up from the forks of the Don near the Elevated Wetlands, there is a small site which has seen some furious construction activity. Toronto Water has built a new sewer outlet which will empty out directly into the Don River.

It is of course their fervent hope that it will not be used but recent discoveries in the trunk sewer beneath the valley led to this construction. As reported in the news early January, cracks were discovered in a Coxwell Trunk sewer pipe that services nearly a million Toronto residents. The city does not know the full extent of the damage nor do they know if or when the pipe will fail. But being sensible people, they need to plan for the worst case. This worst case scenario would mean that the sewage water flowing through the pipe would need to flow somewhere and right now that means directly into the Don River.

Other contingency plans are also in the works. The main plan is to build a diversion pipe around the damaged pipe so that the flow can be directed into a parallel pipe around the damaged section. This will cost between 7-30 million dollars and take 12-18 months to build. In the event that something occurs in the interim there are a couple of emergency options:
  1. Pictured above. Divert the flow into the Don River. Allow it to flow down to the harbour where a PVC curtain will be anchored stopping the effluent from reaching the lake. The water will be pumped out and directed toward Ashbridges Bay Treatment Plant.
  2. Direct the flow to the North Toronto Treatment Plant. This plant now services parts of Leaside and the Yonge Eglinton area. There is an overflow pipe from this plant to the damaged trunk sewer. It would be possible to reverse the flow in this pipe back to the treatment plant. The NTTP is way too small to handle the complete flow from the Coxwell Trunk Sewer but could do primary treatment before sending into the river
  3. Build a temporary pipe above ground around the damaged section. This could be built along the Don Valley or above ground on Coxwell Avenue. This one doesn't sound very palatable and would cause major disruptions in traffic and pedestrian flow in this neighbourhood.
Toronto Water is also doing due diligence with the rest of the system and so far they have investigated pipes in downtown Toronto and the rest of the Don. They are happy to report that no other major problems have been found, although they still have to investigate systems in Scarborough and Etobicoke.

Additional construction will start later this spring when they start to bore a hole underneath the valley for the diversion pipe. It is is hoped that this can be done with a mininum of disruption to the natural environment. Let's all cross our fingers and hope that this is a successful project.

Toronto Water built a temporary bridge across mouth of Taylor-Massey Creek

Barbara Crescent is an unassuming street in East York. The damaged sewer pipe is directly beneath this line of markings on the street

Ominous street markings indicate what lies beneath

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