A $42 million upgrade of sewer and stormwater drainage systems that is part of Edmonton's Capital City Revitalization Levy (CRL) plan could begin in early 2015 if city council passes the needed borrowing bylaw and the capital construction project this year.
“Once that is finalized, we can continue the design stage and move into construction,” said city engineer John Cairns, a project manager for drainage services.
“The project is considered one of the largest upgrades of the city’s drainage system and may entail the use of a tunnel boring machine for 2.4 kilometres to build a new stormwater trunk line running through the downtown revitalization area.
“We will be using trenchless technology,” said Cairns, project manager.
A boring machine will burrow a path for an eight-foot diameter (2340 mm) sewermain, which will be buried 24-26 metres below the surface.
The storm water sewer trunk line will serve as the backbone of the much-needed infrastructure upgrade.
“This piece of infrastructure is critical to service future development in the downtown,” the CRL plan said.
“It will reduce the frequency of basement and surface flooding within the CRL area and will reduce the risk of combined sewer overflow to the North Saskatchewan River.”
Edmonton, like many other larger cities, is rejuvenating its downtown core as more individuals opt to live in central areas.
In April, council received approval for provincial funding support for its CRL plan, which the Downtown Business Association anticipates will spur $4.8 billion in new development over the next five to 10 years.
The system dates back to the early 1900s. Population and climate change is expected to place greater demands on Edmonton’s sanitary and stormwater sewer systems.
The area slated for an upgrade within the CRL plan is currently using a combined system that sees sanitary and storm water going into one sewer.
“Combined systems were the standard until the 1960s, almost everywhere in the world,” said Cairns.
In 1962, Rachel Carson’s book Silent Spring, became a scientific treatise linking population’s impact on the environment, including drinking water. Cities began building separate systems.
Edmonton has embarked on both with separate lines for sewer and drainage water in new construction, but in the older areas, the city has been operating on an “opportunistic” way to separate out lines from the older combined system, said Cairns.
The city’s new revitalization program provided the impetus for partial separation, an alternative outlined in the revitalization plan.
It is intended to provide a reasonable level of service (one in five year event).
It has a lower cost than total separation and does not adversely affect downstream systems.
The old combined system in the area has a low service rate of one in two years or the potential to flood every second year.
Cairns said that sizing the sewers to carry the runoff for a one in five year event is an effective service level.
The city has a policy in place policy for new downtown development, which requires developments to control runoff ranging from a one in 100 event to a one in five year event.
This is achieved by water storage and slow release on site to low impact strategies such as recycling water, using green roofs and bioswales.
The city’s method of separating the combined system has been to build a second line for storm water sewers to reduce the amount of rainwater going into the combined system.
The city has been slowly separating out the systems.
In the 1970s, a nine-foot (2775 mm) stormwater trunk line was built on 111 Avenue in the downtown area.
“We will connect to it,” said Cairns.
The new trunk line carrying storm water will run north along 105 Street hooking into the 1970s line at 111 Ave.
New storm sewers along 100, 102, 105 and 108 avenues, are also proposed.
These lateral storm sewers will connect to the new 105 Street backbone pipe and provide connections from the new developments.
“Because of all the laterals, you have an outlet for any new storm sewer you put in,” he said.
“When areas are redeveloped, they will have separate storm water and sanitary laterals that connect to storm water and sanitary sewers separately.”
He added that some of this work has already started in the nearby Quarters areas following a study in 2009 that laid out a similar plan. T
The older combined sewer is often renewed and converted to function as solely a sanitary sewer.
Edmonton has continued to invest in infrastructure upgrades and last year $230 million was earmarked for work in 56 neighbourhoods, with a portion of the funds going to upgrade sewer and drainage pipes.