After descending into Montreal's sewer system on Thursday, Mayor Denis Coderre says he's confident he made the right decision to go through with the repairs and dump eight billion litres of wastewater into the St. Lawrence River.

"Better to have a plan than just wait for the worst," Coderre told reporters at an afternoon news conference, saying the "corrosion" in the system needed urgent repair. 

Coderre was seen sporting gloves, a helmet and a special protective suit as he was lowered into the sewer in a construction elevator earlier Thursday.

The city has explained it needed to shut down an interceptor — a major sewer that collects the effluent from a network of other sewer lines on its way to the water treatment plant — for maintenance and to link it to a new snow dump site. The wastewater will be diverted into the river as a result.

The construction work began at midnight on Wednesday and Coderre said Thursday it's slightly ahead of schedule.

Coderre said Montreal would take steps to ensure it doesn't have to dump untreated sewage again, telling reporters the city "will build some new infrastructure to prevent what happened this week."

Update on repairs

The City of Montreal reported Thursday that work is ahead of schedule and shared this detailed list of the repairs:

- Southeast interceptor About 25 workers have been toiling around-the-clock to inspect, repair and clean up the southeast interceptor, one of three massive drains that carries wastewater from the island to the Jean-R.-Marcotte sewage treatment plant.

- Riverside Structure Six of 56 deteriorated steel hangers were removed as of 7.a.m. Thursday. These 15.7-metre hangers represented a risk and a nuisance to the drainage capacity of the interceptor.

- Joliette, Dickson, Clarence-Gagnon and De LaSalle Structures Cleaning has been completed and inspections are underway.

- McGill structure Crews are still working to replace the temperature sensor .

- Wells Station Work has begun on the effort to replace the rails at the well of the south gate of the John R.-Marcotte Station.

- Water tests have been taken and the results should be known in 48 hours. A visual inspection has revealed what experts are describing as a "weak plume" around the Old Port and some other discharge points.

- Sediments and plants are being removed in the areas of Nuns Island and the islands around Sorel.

More information here.