City installs separator to treat runoff at its source
By Winston Tang, P. Eng., and Becky Metivier
Victoria, the provincial capital of British Columbia, Canada, is located on the southern tip of Vancouver Island, separated from Washington State by the Strait of Juan de Fuca and the Strait of Georgia. Once a major port for trade and commerce, today Victoria is a world-renowned tourist destination known for its moderate climate, natural beauty, and recreation sites.
Environmental stewardship, therefore, is a strong community value, and protection of natural resources is essential.
Additionally, preventing and controlling stormwater-borne pollution is a priority of Environment Canada’s Georgia Basin Action Plan. (Environment Canada is a national regulatory agency, like the U.S. Environmental Protection Agency.) Among the plan’s goals are to protect and restore key ecosystems and to support conservation, protection, and restoration of the environment through sustainable land, aquatic, and resource use planning and management (www.pyr.ec.gc.ca/georgiabasin).
Consequently, maintaining water quality has come to the forefront of environmental concerns, and city officials have undertaken many stormwater pollution-prevention initiatives.
"Mitigating non-point source pollution requires a combination of innovative approaches, from pollution prevention-based solutions in the watershed to managing water quality at the end-ofpipe," said Laura Mclean of Environment Canada.
As with many municipalities, Victoria’s storm drainage system discharges urban runoff directly into the adjacent harbor without any treatment. Pollutants such as sediment, oil, grease, and trash contained in untreated stormwater runoff from parking lots, roadways, and industrial sites can cause great harm to marine environments.
A survey by one federal agency identified Rock Bay as the most polluted bay in the Victoria and Esquimalt Harbors, and stormwater runoff was determined to be the primary source. The bay is located alongside a six-lane roadway that serves as a major throughway into the city. The existing storm drain discharged storm flows from a predominantly impervious (paved), 81.3-acre area with a history of industrial land use.
To curb this pollution, city officials decided to treat the runoff at its source—the stormwater outfall at Rock Bay.
Working with Consulting Engineer Troy Jones, P.Eng., formerly with Kerr Wood Leidal Associates, Victoria, B.C., the city began a comprehensive search for stormwater treatment systems that would work within the site’s space, groundwater, and underground utility constraints and also provide the necessary pollutant removal.
Ultimately, the Vortechs® system, a hydrodynamic separator by Vortechnics, Inc., Scarborough, Maine, was chosen. Non-mechanical and gravity driven, the Vortechs system uses a patented combination of vortex action and flow controls to capture pollutants and retain them throughout storm events. However, because such units are relatively new in Canada, Jones wanted a documented performance record for the system.
Vortechnics was the only manufacturer able to provide independent, field-testing data of its system showing that it was capable of meeting the necessary standards.
Connecting the Vortechs system to the existing infrastructure, however, created multiple challenges. The separator system was installed directly underneath the roadway among many utility and fiber-optic cables, limiting the amount of space available for installation. And, because of the site’s close proximity to the shoreline, tides and high groundwater had to be considered.
After reviewing 28 years of precipitation data, officials determined that flow from the large drainage area could reach rates as high as 31.1 cubic feet per second. Few standard-sized treatment systems are capable of treating flows of this magnitude, however, Vortechnics offers a high-volume, cast-in-place system, which was chosen for the Rock Bay site. The relatively small footprint of the system—12.5 feet high, by 17.4 feet wide, by 24.3 feet long—made it compact enough to fit into the tight site. The system was sized to treat 39 cubic feet per second while removing 80 percent of the annual total suspended solids (TSS) larger than 50-microns.
Victoria began installing the system in late August 2003 and finished the project about one month later. The Vortechs system’s horizontal design gives it a low profile that requires only a shallow excavation. Less excavation decreased installation time and diminished the need for dewatering in the high-groundwater environment.
By installing the stormwater system, Victoria became one of the first cities in Canada to treat urban runoff prior to discharge into a marine environment. "Improving surface water quality has been an important goal of the city for many years," said Gary Pleven, Victoria’s pollution abatement officer. "This passive system technology will reduce the amount of sediments, oils, and debris being released into the harbor." Since installation, visual inspection of the Vortechs system’s inlet/grit chamber compared with the last baffle wall at the outlet end has demonstrated capture of sediment, oils, and grease. Pleven said that he has been pleasantly surprised by the amount of sediment, oil, and trash that has been collected by the system.
Of course, installing the system is only the first step in ensuring stormwater pollution prevention. Like all stormwater pollutant-removal systems, periodic inspection and maintenance is essential to guarantee long-term performance. The Vortechs system offers unobstructed access to accumulated pollutants through a manhole on top of the unit.
Maintaining the system also will be cost-effective because it has a small pump-out volume.
Victoria’s proactive approach to stormwater pollution has made it an example of environmental stewardship for the province and the country.
Stricter stormwater regulations for the region will follow. In the meantime, Victoria plans to stay at the forefront by continuing to install additional stormwater systems throughout the city, removing pollutants that previously ended up in its harbor.
Winston Tang, P.Eng., is president of EST Environmental Technologies, an exclusive representative for Vortechnics in western Canada based in North Delta, B.C. He can be contacted at 604-502-8332, or via e-mail at email@example.com. Becky Metivier is a marketing specialist for Vortechnics, Inc., Scarborough, Maine. She can be contacted at 207-885- 9830, or via e-mail at firstname.lastname@example.org.