Boil water advisory in Montreal caused partly by old pump

Montreal suffered its largest boil-water advisory ever in its history at the end of May after its historic Atwater water treatment plant malfunctioned. The plant, which opened in 1918 and continues to service large portions of the city, is undergoing $150-million in upgrades, including adding ozonation and ultraviolet disinfection.

City officials reported last week that the 36-hour problem of turbidity May 22-23 was caused by a series of events, starting with workers trying to remove a membrane from one of the reservoirs. They allowed the water in the reservoir to drop too low, which in turn caused water in the final reservoir to drop, stirring up sediment in the bottom. Then when a 60-year old pump failed to turn off automatically when it began sucking in air, muddy water was distributed out to 1.3 million Montrealers.

Fortunately tests showed no harmful contamination, but the water coming out of the taps was an unappetizing brown colour. The incident occurred overnight and was discovered at 6.30 a.m., but it took three hours until Montrealers were alerted.

By coincidence the Atwater Plant was being celebrated by the Canadian Society for Civil Engineering (CSCE/SCGC) a few days after the plant had the malfunction. The society designated the plant as a national Historic Civil Engineering Site at its annual meeting held in Montreal May 29-June 1.

The city said the accident was caused by “an unforeseeable and simultaneous chain of events,” not human error. It is looking into improving the training of operators and their supervision. In Quebec plant operators only have to do one year of training for certification, compared to four years in many cases in Ontario.

The Atwater Plant draws its water from the St. Lawrence River and can process over 1.3 million cubic metres of water per day, with an average daily treatment of 700,000 cubic metres per day. Since its inauguration nearly 100 years ago, it has had seven expansions, the last in 1967.