Metro Vancouver's Sanitary Sewer Overflow Storage Facility captures sewer overflows

Central flushing system in mechanical room

Like many established urban areas in North America, Metro Vancouver, previously the Greater Vancouver Regional District, has an aging sewer system. With age, sewer systems can become subject to increased infiltration and inflow. This was the case for the sanitary sewer collection systems in the Cloverdale and Surrey Central Valley areas of Metro Vancouver. The sewer systems were subject to excessive infiltration and inflow during substantial rainfall events. This had the potential to cause sanitary sewer overflows at the Cloverdale Pump Station, which could flood adjacent lands and ditches.

As part of Metro Vancouver's Liquid Waste Management Plan, Metro Vancouver made a commitment to capture sanitary sewer overflows arising from 1 in 5 year intensity storms. Metro Vancouver reviewed a number of alternatives and a decided to add peak flow storage upstream of the Cloverdale Pump Station.

Metro Vancouver retained Associated Engineering to design the new Cloverdale Sanitary Sewer Overflow Storage Facility. Associated Engineering completed design of the facility in 2003, and Metro Vancouver crews completed construction of the new facility in September 2007.

Tank site

The new facility automatically diverts sanitary sewer overflows into the 6,700 cubic metre, 44 metre diameter, circular storage tank, and returns the stored flows back to the Cloverdale Pump Station after the storm. A flushing system using retained wastewater held in a central column under vacuum cleans the floor of settled solids after each storm event. The use of this flushing system is the first in Canada. Two on-site buildings provide access to the tank, and house the electrical and mechanical equipment. All major equipment is contained above-grade, minimizing the need for operators to enter the tank for equipment servicing.

The facility embraces Metro Vancouver's Sustainable Region Initiative by protecting the environment through the significant reduction of sanitary sewer overflows into the environment and by incorporating a number of sustainable design features within the facility. Sustainable features of the facility included:

• Reusing wastewater for flushing and cleaning, thereby significantly reducing use of drinking water for this purpose
• Using high-volume fly ash concrete (which also provides improved chemical resistance) to reduce the greenhouse gas emissions associated with Portland cement production
• Using natural and wetland grasses for landscaping
• Reusing existing soils
• Optimizing material use (circular compared to rectangular tank)
• Incorporating energy efficiency by allowing the tank to completely fill under gravity conditions and drain about 40% by gravity
• Using an innovative control approach to maximize the storage capacity using control gates.

Metro Vancouver's Project Manager, Chris Squire reports, "As of midNovember, the facility has been used a number of times to prevent sanitary sewer overflows into the natural environment."

This facility was part of the Metro Vancouver submission which received the 2003 Professional Engineers and Geoscientists of BC's Sustainability Award.

Metro Vancouver Engineering and Construction Team