William and Saint-Thomas retention infrastructure

Last updated May 27, 2021
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When completed, the William and Saint-Thomas retention facilities will reduce the frequency and amount of untreated wastewater discharged into the St. Lawrence River during major rainstorms. Two parks will be created above the retention basins.

William water retention basin

  • Location: between Rue Ottawa, Rue Ann, Rue William and Rue Dalhousie
  • Start of work: April 2018
  • End of work: July 2019
  • Water retention capacity: 12,000 cubic metres (a bit more than four Olympic-size swimming pools)

The William water retention basin:

  • Collects stormwater during high intensity meteorological episodes to prevent sewers from overflowing, which would lead to discharge into the river
  • Supports the sewer system capacity in the quickly developing Griffintown district

In time, parc Mary-Griffin will be created above the William retention basin.

William retention basin
  • maquette du bassin de rétention WIlliams

Saint-Thomas retention basin

  • Location: between Rue Ottawa, Rue Saint-Thomas, Rue William, Rue de la Montagne and Rue du Séminaire
  • Deconstruction of building: work completed in 2019
  • 2021: feasibility analysis underway
  • Basin with capacity of about 15,000 cubic metres (about six Olympic-size swimming pools)
  • Bypass structures at the Saint-Jacques/de la Montagne intersection and at the William/de la Montagne intersection
     

The Saint-Thomas water retention basin will:

  • Collect stormwater during high intensity meteorological episodes to prevent sewers from backing up
  • Support sewer system capacity in the quickly developing Griffintown district
  • Protect St. Lawrence River water quality by reducing runoff 

In time, Parc des Eaux-Cachées will be created above the Saint-Thomas retention basin.

Saint-Thomas retention basin
  • Maquette du bassin de rétention Saint-Thomas

Construction of a service building 

During 2021, a service building will be constructed on the site of the William retention basin, which was built underground. This site is between Rue William, Rue Dalhousie, Rue Ottawa and Rue Ann. It will provide electrical and mechanical services to the retention basin. The wastewater treatment plant located on the eastern part of the island will manage the filling and emptying of the water basin remotely.

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