Clean Production and Toxics

Sewage in the St. Lawrence: Problems and Solutions

Only forty to fifty years ago, it was possible to swim in the St. Lawrence River, even around Montreal. However, the rapid growth of Quebec’s population from the 1950s to the 1970s brought with it an increase in industrial wastes, domestic sewage, and agricultural pollution. The deterioration of water quality was coupled with urban and rural development which destroyed many natural habitats.

In part 1 of a 2 part series exploring sewage in Quebec, HÉLÈNE GODMAIRE of Great Lakes United reviews the problems facing six cities.

In response the deterioration of water quality, federal, provincial and municipal political stakeholders joined with scientists and researchers to restore and protect the ecosystem. It was not until the late 1970s that wastewater treatment initiatives began, twenty years after communities in the upstream Great Lakes began addressing sewage pollution.

Along with Ecojustice and Eau Secours, Great Lakes United has been working to update the Great Lakes Sewage Report Card for St. Lawrence River cities. Published by Ecojustice (then Sierra Legal Defence Fund) in 2006, the Great Lakes Sewage Report Card graded twenty cities across the Great Lakes in Canada and the United States in terms of the quality and capacity of their sewage treatment systems to prevent pollution from entering the Great Lakes.

The Quebec work looks at six communities along the St. Lawrence River, and finds many of the same challenges that Great Lakes cities faced. At the top of the list are combined sewage overflows and cross-connections between sanitary and storm systems.

The report, to be released later this fall, analysed data filed with the Québec Ministry of Municipal Affairs and Regions for 2004 to 2006. The six communities under investigation were Montréal, Laval, Québec City, Longueuil, Trois-Rivières and Salaberry-de-Valleyfield.

Every year, cities across the Great lakes and St. Lawrence river watershed dump over 90 billion of litres of raw sewage into the lakes and the river. These discharges affect water quality, threaten human health, degrade the natural environment and limit recreational activities. From Duluth to Gaspé, municipal sewer and wastewater treatment systems allow a toxic cocktail of chemicals, pharmaceuticals, and coliforms to enter our lakes and rivers.

A glass half full… of sewage?

In Montreal, the sewage treatment plant located in Rivière-des-Prairies has served the entire city since 1996. The plant treats the waste of nearly 1.8 million people, and 9,500 industries, businesses, and other institutions. This is between 2.5 million and 7.3 million cubic meters of water every day: nearly half of all the wastewater in Quebec.

Montreal’s sewage treatment plant is the largest primary-physicochemical treatment facility in North America, using a combination of physical and chemical processes to treat the water. This treatment allows the removal of approximately 50% of coliforms and significantly reduces biological oxygen demand (BOD, a measure of the degree of pollution), eliminates almost all suspended solids, and removes a portion of pollutants and phosphorus.

The process, however, does not adequately eliminate some contaminants such as heavy metals, cyanide, phenolic compounds and pharmaceuticals. At the same time, the control of chemicals at their source is not systematically accomplished, and hundred of industries can release toxic chemicals in their wastewater to the plant or directly into the river. Despite tremendous efforts to reduce pollution from the treatment plant, discharges are a major source of pollution in the St. Lawrence River.

Also, treatment at the station is incomplete because there is no disinfection technology in place. Initially, the Montreal wastewater treatment plant design included a disinfection process using chlorine, though it was never implemented prior to being banned several years ago. The use of chlorine in wastewater treatment was shown to pose risks to aquatic life and public health.

After years of study, Montréal has recently selected ozone as the best type of disinfection. Optimistically, the process should be operational in a few years. Ozonation is capable of removing a much greater variety of chemicals, pharmaceuticals, and personal care products than other alternatives.

The Flow from Flush to Treatment

As in many older cities in North America, wastewater from homes and businesses flows into the same pipes as storm water from the streets. This combined sewer then directs water to the treatment plant for processing.

During heavy rainfall or snowmelt, the sewer system and treatment plant can be quickly overwhelmed. To prevent water from backing up into homes and basements, excess sewage is sent directly into St. Lawrence River without treatment. These overflows can last for a few minutes, or up to several hours. In many cases, this degrades water quality and contributes to the beach closings that come in the wake of summer storms.

Among the six cities under study, combined sewer overflows are a common problem. While the volume released in overflows is not known, the duration and frequency of overflow events indicate a significant problem.

In Laval and Salaberry-de-Valleyfield, combined sewer overflows occur even during dry weather. In these cases, the networks cannot handle the volume of wastewater generated by residents and industries. The city of Salaberry-de-Valleyfield seems to have progressively addressed the problem as dry weather overflows decreased over the three years of study. However, in Laval the problem persists, with approximately 350 overflows (site events) per year.

In Montreal, two-thirds of the island is served by combined sewers, leading to significant overflow potential. In the remaining third of the city, the sanitary and storm water systems are separated. The storm water is directed back to the St. Lawrence River, while the sanitary water is treated at Rivière-des-Prairies. A common challenge in this part of the city is sanitary systems that are accidentally or illegally cross-connected to the storm water system. In this case, sanitary waste is released back into the St. Lawrence all year without treatment. As a result, high coliform concentrations can be found at the storm water outfalls.

Just as sanitary waste is incorrectly diverted to the storm system, there is also a problem of sump pumps that are mistakenly connected to the sanitary sewer causing an excessive volume of water to be treated at the plant.

Steady Improvements in Montréal

Over the past 25 years, the city of Montréal has invested over $1.4 billion in upgrading its sewage system. Understanding that the environmental, physical and economic health of the city depends on high quality water, the city has committed to protecting the environment in all phases of water treatment.

In the last three years, over $40 million has been dedicated to correcting cross-connections, completing infrastructure work, constructing retention reservoirs to prevent overflows, and setting up a real-time control system to maximize the amount of wastewater treated during rain. The city will invest over $550,000 alone annually for the next three years in a program to correct cross-connections.

In addition to upgrades of the water infrastructure and better wastewater management practices, Montréal has developed a Water quality Monitoring Network to measure the quality of water across a number of locations and for a variety of chemical and biological contamination. These studies are showing steady improvement in water quality across the island, with just over half of 115 shore water monitoring sites showing that the water is safe for direct contact and recreational activities. Unfortunately, the extreme north and east shorelines have shown no progress in terms of shorewater health. Much remains to be done to improve the picture. These solutions will be explored in the next edition of Great Lakes News.

Great Lakes United will be working with Ecojustice to promote green infrastructure solutions. For more information contact Hélène Godmaire at helene@glu.org.

Research conducted in collaboration with Andréanne Demers of Eau Secours.

© 2008 Great Lakes News.