Stacked stormwater storage

February 2013 » Features » PROJECT CASE STUDY
Flexible design of underground system adapts to site conditions and capacity requirements.
Triton Stormwater Solutions' double-stack design allowed developers to create 22,000 cubic meters of stormwater storage in a 20-meter by 70-meter area for a new retail center in Toronto, Canada.

Engineers from Terrafix Geosynthetics needed a high-quality, high-strength, high-volume underground stormwater management system to support construction of a 600,000-square-foot retail center in Toronto. Along with handling and storing the site's stormwater runoff efficiently, the system also needed to protect municipal storm sewers.

Project
Underground stormwater management system, Toronto, Canada

Participants

Terrafix Geosynthetics
Topsite Contracting Ltd.

Product application

Triton Stormwater Solutions' chambers in a double-stack configuration provide 22,000 cubic meters of underground stormwater storage in a 20-meter by 70-meter footprint.

The Stockyards development will be home to a host of premier retailers when it opens in the fall of 2013. The project demanded a small stormwater footprint with enough capacity to store the runoff from both the shopping area and parking lots. Additionally, a premium was placed on system flexibility. The project team needed a system that was adaptable enough to work with the existing site infrastructure, including a storage tank and large-diameter underground pipe.

An added challenge was posed by the fact that the system would need to be strong enough to be buried 24 feet below the surface, under the loading dock area, when finished.

Consultation between Triton Stormwater Solutions' engineering staff and Terrafix Geosynthetics led to selection of Triton Stormwater Solutions' double-stack configuration. Independently tested and approved for such a stacked configuration, the chambers allow engineers to increase the amount of storage dramatically without expanding the project site. In the case of the Stockyards project, the small-footprint system was able to achieve 22,000 cubic meters of storage in just a 20-meter by 70-meter area.

The system's flexibility also was critical to the project's success. Project engineers used an existing large-diameter pipe as a preliminary main header row. Water was gathered in the large pipe and then fed to a smaller main header row ahead of each distribution row.

"Since Triton Stormwater Solutions already has the 'standard' practice of incorporating a main header row, we are good at adapting to a wide variety of scenarios to accommodate site-specific challenges – whether that is the need for extensive pretreatment options, sediment catch basins, or something like adapting our plan to utilize the existing inlet pipe as a part of the overall system," said Joe Miskovich, president of Triton Stormwater Solutions

By incorporating the existing pipe as a preliminary main header row distribution mechanism, the initial project costs were contained within budget. The system design also will save money in future maintenance costs by providing a large access point by which to maintain the system. Stormwater sediments will settle out on the specially designed main header row floor for easy removal through integral maintenance ports, protecting the distribution rows from debris build-up and the resultant sediment clogs that cause drainage problems.

The project also featured a special oil separator as part of the inflow, allowing the system to be used to remove hydrocarbons from the incoming stormwater. This will help protect downstream water quality without costly post-storage mitigation. The ability of the system to work with a wide range of pretreatment devices makes it a good choice for areas with strict water quality regulations or specific environmental concerns. Triton Stormwater Solutions also offers a filter elbow and stainless steel puck system that allows developers to target specific contaminants with easily changed filter media inside the stainless steel puck.

Using an underground stormwater management system to closely replicate predevelopment hydrology for projects working to earn LEED credits can contribute as many as 18 credits. Additionally, the chambers' reinforced, structural, soy-resin-based construction assists those pursuing sustainability mandates or working on environmentally sensitive projects.

A pre-existing large-diameter inlet pipe was converted into a preliminary main header row.

Installation
After initial site preparation, the double-stack of nearly 2,000 Triton chambers was installed in a day and a half by a four-man crew from Topsite Contracting Ltd. A PVC non-molded liner and non-woven geotextile fabric, along with layers of 2-inch crushed stone, also were used to support stormwater drainage and storage at the site.

The combination of the chambers and the impervious fabric layer served as a low-cost alternative to the originally proposed concrete holding reservoir. Water will be held in the storage area and pumped out intermittently to maintain the desired outflow from the site and to protect the city's storm sewers.

"The Triton Stormwater Solutions system was a cost-effective solution," explained Rob Hughes of Terrafix Geosynthetics. "The chambers were extremely lightweight and could be installed by hand, without any mechanical assistance. The installation was easy, and ran smoothly."

Because of the chambers' strength, the crushed stone could be spread quickly with rock-slinger trucks, thus reducing the time needed for this phase of the installation by nearly half.

This article was contributed by Triton Stormwater Solutions (www.tritonsws.com).


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