This Canadian storm water system consists of two sections – a network of pipe & a pair of underground storm water retention units
One of the key components for turning part of this former industrial park into a 2,000 unit residential, pedestrian-oriented development – POD - was the storm water system. With a total of 165,367 square meters (1,780,000 square feet), Candiac Square is located on the southern portion of the Montcalm Industrial Park, close to one of the main entrances of the city of Candiac and 20 minutes by public transportation to downtown Quebec. Developers and the city wanted to revitalize the area using sustainable practices with a focus on the benefits of nearby municipal transportation. The $600 million Candiac Square, formerly the site of the Consumers Glass factory built in 1966, community revolves around a large central park of 10,000 square meters (107,639 square feet). Nicknamed “Nature at the Square,” the contemporary residential community is a green housing project with more than 17,000 trees and its own rainwater recovery system.
The storm water system, installed in two phases from early 2017 and completed in 2019, consists of two sections – a network of pipe and a pair of underground storm water retention units. Both used high-density polyethylene (HDPE) pipe, which would meet the municipal and provincial governments requirements for storm water management. The system was designed by engineering consultants S.M. Group International Inc., now FNX-INNOV, Inc., (Montreal) and installed by A & J.L. Bourgeois Ltd (Quebec).
For the first part of the storm sewer network, Bourgeois installed more than 630 linear meters of 1,200 millimeter (48 inch) diameter HDPE pipe as well as 15 chimney-type 900 millimeter (36 inch) manholes, which were welded directly to the pipe. HDPE pipe in diameters ranging from 450 millimeters (18 inch) to 1500 millimeters (60 inch) was also used. The corrugated HDPE pipe from Soleno Inc. (Quebec City), called Solflo Max, is AASHTO M294 certified, meets ASTM standards for F405 and F667 and complies with Canadian Standards Association, CAN/CSA B182.8.
To treat the retained water, an AS-10 Aqua-Swirl hydrodynamic separator was added at the end of the pipeline before it connects to the city storm sewer. More than 1,290 linear meters (4,232 feet) of HDPE pipe formed this storm sewer network.
For each of the two 16-row retention systems, nearly 480 HydroStor HS180 chambers were installed on a stabilization geogrid and then surrounded by clean stone covered with TX-90 geotextiles. The first retention basin designed for heavy rain events can store up to 2,505 cubic meters (88,463 cubic feet) of water, and the second retention basin has a capacity of 2,475 cubic meters (87,403.8 cubic feet) of water. A waterproof geomembrane as well as two protective geotextiles were installed on the two excavated areas, measuring 35 meters (115.7 feet) in width and more than 66 meters (216.5 feet) in length.
According to the Plastics Pipe Institute Inc. (PPI), the polyethylene resin produced for the pipe provides a favorable strength-to-weight ratio. It also makes HDPE pipe easy to handle, and freedom from degradation by soils, chemicals, ambient water and moisture, therefore, will not corrode or rust it. Because HDPE is a non-conductor of electricity it is immune to the electrochemical-based corrosion process that is induced by electrolytes, such as salts, acids and bases.
HDPE pipe is not vulnerable to biological attack or tuberculation, is resistant to bio-clogging and maintains high, consistent flow capacities throughout the service life of each system. PPI is the major North American trade association representing all segments of the plastic pipe industry. The pipe manufacturer, Soleno, is a member company of PPI.
“Corrosion, abrasion, de-icing salts and vibration resistant, the use of HDPE ensures the resiliency of the infrastructure,” said Daniel Currence, P.E., director of engineering for PPI’s Drainage Division. “This storm sewer system made completely of HDPE, an efficient and durable material, provides longevity for Candiac Square. Lightweight and easy to handle, HDPE products did not require the use of specialized equipment, such as a crane, making the installation easier and quicker. The length of the Solflo Max pipes reduced installation time as well as the number of joints between pipe sections, compared to traditional concrete pipes.”
The HDPE manhole does not require it to be oversized, which provided substantial savings both in terms of the purchase price and excavation-installation costs. Its welded HDPE design made it possible to assemble the inlets and outlets at the factory so that connecting on the job site was efficient. Another feature of the manhole is its smooth exterior wall which prevents vertical movement during freeze and thaw cycles.
Due to the watertight bells with O-ring gasket (BG) or with integrated gasket (BGI) - patented and exclusive to Soleno – the slightly oversized, Solflo Max pipes quickly fit together. Fitted with clips to validate the quality of the installation as well as the depth of the nesting, the use of watertight bells provides powerful joints and ensures the watertightness of the storm sewer network. The HydroStor HS180 retention system, made of polypropylene and HDPE, is easy to install, due to the lightweight retention chambers. Designed for heavy volume or restricted space projects, each chamber can store 5.1 cubic meters (180.1 cubic feet) of storm water, making them more cost-efficient by greatly reducing the area of the burial pit.
The installation of a geogrid helped to ensure a solid and stable foundation at the base of the chambers by distributing linear workloads over a larger surface area. Installed at the outlet of the storm sewer, the Aqua-Swirl treatment unit retrieves suspended solids, oil and grease, while ensuring the system’s sustainability. Its direct access from the surface eliminates the need for work in confined space and facilitates the periodic maintenance.
“Today, there is a growing expectation by communities for sustainable and resilient products,” said David M. Fink, president of PPI. “We, as an association, agree, and our members also believe, that HDPE pipe can meet and even exceed those expectations. This practical, long-life storm water network made entirely with HDPE products won over the city of Candiac, and the residents of Candiac Square will benefit for many years to come.”