260,000 gallon detention system, CSO wet weather facility, 17 prefabricated barrel sections (480 LF of 5’ diameter, 433 LF 6’ diameter, 360 LF 7’ diameter), 3 prefabricated manifolds with access risers
Ville de Sainte-Agathe-des-Monts (Sainte Agathe) is a popular, four-season tourist destination in the Laurentian Mountains in the province of Quebec. Sainte Agathe was first settled in 1849 and saw rapid development in the early 1900s. This historic city’s sewer system is a combined system that conveys both sanitary sewer and stormwater discharge into the local municipal wastewater treatment facility. Combined sewers were a common approach to municipal sewer design in the first half of the twentieth century, when there was little focus on their environmental impact. In the case of such a system, the prime challenge lies in the fact that municipal wastewater treatment facilities are not typically designed for the treatment of the higher discharge rates and volumes associated with most rainfall events. Their discharge into streams and rivers is known as a combined sewer overflow (CSO) event and has been subject to tightening environmental regulation over the last 20 years.
A new Weholite detention facility is helping to protect a town’s pristine streams and rivers and fulfil the CSO regulations adopted by the Canadian Council of Ministers of the Environment in Ville de Sainte-Agathe-des-Monts, a popular tourist destination in Quebec, the largest province in Canada.
Protecting pristine streams and rivers
On February 17, 2009, the Canadian Council of Ministers of the Environment (CCME) adopted the Canada-wide strategy for the management of municipal wastewater effluent. Although Quebec has not yet formally signed up to the strategy, it has declared its support for the strategy’s technical content and aims to ensure that its criteria for land development or redevelopment projects include at least the Canada-wide overflow standards established by the strategy. To protect the town’s environment and fulfil the aims of the CSO regulations adopted by the CCME, Sainte Agathe commissioned a large-scale combined sewer detention facility adjacent to its municipal plant, along the Riviere du Nord. The detention facility is designed to store 260,000 gallons (984 m3) of stormwater discharge during peak flow events. This additional storage capacity effectively eliminates CSO events during all but the largest storms and serves to protect the town’s pristine streams and rivers.
Completely leak free system
A variable rock table and existing infrastructure constraints required that the system be based on multiple diameter barrels in a three-field approach. Infra Pipe worked with the engineer of record at SMi Consultants, to develop a system that would provide the required storage volume while minimising rock excavation and the impacts on the plant’s existing infrastructure. The detention system was fabricated from a Weholite RSC 250 profile wall polyethylene pipe manufactured in accordance with ASTM F894. Its barrel geometry included 5’, 6’, and 7’ diameter barrels connected by a continuous 36” header system with 36” manhole access risers. Bulkheads were manufactured from a Wehopanel P120H profile wall panel and reinforced with PE-HD encapsulated steel beams. Large-scale underground detention systems require a comprehensive, engineered-systems approach to design.Infra Pipe evaluated the Sainte Agathe system using a 2-dimensional (CANDE) finite element analysis routine, which accounts for soil-structure interaction under the applied loads.Infra Pipe also performed a 3-dimensional finite element analysis of the system in order to analyse the bulkhead deflection and reinforcement requirements.Infra Pipe worked with the general contractor, Inter Chantiers, to coordinate the detention system’s fabrication schedule, installation and field welding details. All joints, fittings and fabricated elements were extrusion welded to ensure a leak free system. The fully assembled system was tested under a 24-hour exfiltration protocol and certified as leak free. Upon the successful completion of the project, Alexander Foisy, the President of Inter Chantiers commented: “Inter Chantiers is proud to have successfully achieved this project on schedule and on budget. Our team truly believes that we not only “built another infrastructure project” but that we did so in a sustainable manner. I am proud to have contributed to my community by participating in this project. My two sons may come back to live here in Sainte-Agathe when they grow up and, if they do, I am sure they won’t have to pay for the replacement of our project out of their taxes!“
100-year design life without corrosion
Infra Pipe’s Weholite ASTM F894 profile wall polyethylene system provides a 100-year design life and is resistant to H2S, pH, corrosion, and abrasion. Weholite has been used throughout the world and North America since 1981.Infra Pipe’s systems are manufactured according to strict polyethylene welding standards and can be custom fabricated to meet the needs of any application. All fabricated structures are pressure tested prior to shipment. In-field extrusion welding is performed byInfra Pipe’s certified technicians to ensure that a leak free system is achieved.Infra Pipe is able to provide a high quality system with a longer design life and at a reduced total cost of ownership.