March 26, 2010

CITY OF OTTAWA

Ottawa’s Sandy Hill Flood Control and Park Rehabilitation project incorporates an underground storage tank similar in function to the $140 million facility proposed to prevent sewage overflows into the Ottawa River.

FEATURE | Sewer and Watermain

Ottawa opts for $140 million overflow solution

Ottawa River Action Plan passes on $1.3 billion plan over 60 years

PETER KENTER

correspondent

Ottawa City Council has approved a plan to construct a massive $140 million storage tank facility designed to contain combined sewage overflow (CSO) during heavy rainstorms.

The project was recommended by the city’s department of Infrastructure Services and Community Sustainability under the Ottawa River Action Plan (ORAP).

The report considered three CSO control options. The least expensive involved a $40- to $60-million expansion of existing storage capacity to meet provincial targets, which allow no more than two CSOs during the swimming season in an average year.

The most expensive was an option to virtually eliminate CSOs costing $1.3 billion to $2.2 billion. The program would take 50 to 60 years to complete and included complete sewer separation over a 675-hectare area of the city currently served by a single-pipe system. Separation would be a difficult prospect in this area because it lacks convenient locations to discharge stormwater. The program would also include installation of centrifuges at stormwater outfalls and extensive work on 58,000 households to disconnect downspouts, and install new sewer laterals and basement sump pumps.

“Essentially we approved of the report’s recommendation for the $140-million option, which is in the middle ground for cost,” says Alain Gonthier, manager of asset management with the City of Ottawa. “This option would provide enough additional capacity to exceed the Ministry of the Environment’s requirements, but provide us with a bit more flexibility in the future.”

The plan is designed to reduce the number of CSOs from a current annual average of 30 to only one per year, and allow for treatment of a greater volume of urban stormwater than the least expensive option.

The design for the storage facility won’t be finalized until a provincial Environmental Assessment (EA) is completed some time this year.

“What we do know is that the storage facility will be located along the northern part of the city, close to the Ottawa River,” says Gonthier. “Storage facilities of this kind are usually built of concrete and located below ground. The water would be held in the storage system, then transferred to the treatment facility, either by gravity or pumped back.”

Gonthier says that CSO storage facility could either take the form of a localized storage tank, or a series of linear storage tunnels. The ORAP report notes that if the EA recommends a linear solution, a tunnel extending from downtown to the sewage treatment plant could double as a back-up to the Ottawa Interceptor Outfall Sewer, which is now more than 50 years old.

Ottawa recently completed a similar project on a smaller scale. The Sandy Hill Flood Control and Park Rehabilitation project incorporates an underground storage tank one metre below the surface of a community park. The park project, which incorporates other elements of the city’s flood control and stormwater management plan, was honoured with an Award of Merit in the 2009 Ottawa Urban Design Award competition.

The city is looking to spend almost $252 million, including the cost of the storage facility, over a five-year period, which began in 2009, to stop the flow of raw sewage into the Ottawa River. Other projects include a program to maximize existing capacity in the combined sewer collection system through an upgrade of regulators, and the use of automated controls. The city is also installing traps in city sewers to reduce the quantity of “floatables,” such as plastic bottles, cups, wrappers, oil and grease, which can be discharged to the environment.

Most of the ORAP projects are scheduled for completion by 2013.

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