Grande Prairie Rainwater Harvesting Tank
The Atlantis modules were used as a dual containment system in the city’s new salt storage yard. This design meets the future anticipated Environment Canada and Alberta Trans-portation & Utilities requirements.
The Rainwater tank installation consisted of a 36 m³ retention tank installed under a salt shed (future) and pickled sand pile crib. The in-house design is unique for a few reasons: Firstly, all the rainwater runoff had to be contained. The entire site area of 3 acres was fully lined with an impermeable HDPE membrane placed underneath the asphalt. In addition, the retention tank was also wrapped in an impermeable membrane resulting in a dual containment system. Secondly the underground retention system is to receive surface run-off through a HDPE manhole also connected to the tank. Depth of cover above the tanks is 1.2 m.
All of the collected storm water from this salt shed storage area will be captured and contained within the tank modules for removal at a later stage by vacuum truck. None of the potentially contaminated salt rainwater is able to permeate into the surrounding subsurface. By managing the storm water locally and storing it on site, this tank will prevent contamination of the local groundwater system. The tank system has been designed to provide adequate detention for a one in a hundred year storm.
The assembled modules were shipped to site. Using a crew of 4 people, the total time required to install and complete this phase of the project was four days. This included for the excavation, installation of the modules, connection of the HDPE Manhole, and wrapping with both geo-textile and impermeable HDPE membranes.
The Rainwater tank system was chosen for the following reasons:
• The tanks were found to be an innovative solution for the city’s salt storage and rainwater management issues.
• The product cost was found to be less than a concrete chamber.
• The tank provided maximum utilization of excavated area because the volume of the finished tank is the volume available for detention.
• The installation cost for the tank was also found to be less than the cost of other systems.
• No gravel thrust-blocking was required to sup-port the tank which eliminated the costs associated with excavating for and handling of gravel.
• Due to its high ultimate load bearing capacity yet open structure and open surface area, the tank is lightweight and quick to install.
