March 28, 2008

Infrastructure

Construction of London’s $30-million sewer upgrade and pumping station begins soon

MARY BAXTER

correspondent

Construction on a nearly $30-million sanitary sewer upgrade and pumping station in London’s southwest begins this spring.

“Essentially, the whole project is eventually to service the south end of London and all of the developments in the works going on in the south end,” says Ted Koza, an engineer in the city’s construction administration division, adding the pumping station will replace an existing one designed in 1967 that is at the end of its life.

Because of its magnitude, the project is being divided into three major segments: building the new station, installing 3,800 meters of sanitary trunk sewer to join the existing pump with the proposed one, and adding a 0.75 m diameter forcemain from the station to convey sewage to the city’s west-end Greenway Pollution Control Plant.

Construction is expected to begin in March on the first phase of the project — the 3,800 meters of sanitary trunk and sewer to join the two pumping stations.

Koza explains that the first phase was split into two contracts that were recently awarded: $7.7 million to London-based Bre-ex Ltd. to install 2,400 meters of 1.65 m diameter sewer, and $3.75 million to London-based L82 Construction Ltd. to install 1,400 meters of 1.5 m.

Gravity will help feed sewage along this portion of the system and that means the pipe will have to be “significantly deep” in some spots, he said, estimating depths to reach 32 to 36 feet.

With the depth, there’s “no question” there will be challenges and safety will be paramount, Koza says.

With the pipes going into a clay silt soil, both contractors are proposing open trench excavation, he said. Excavation and installation will take place in short sections to help maintain control.

“There’s a very rigorous excavation and material replacement program that needs to be put in place, obviously, with this,” he says.

Because of the depth of excavation involved, the reuse of excavated material and a required compaction density of 98 per cent, the city is requiring a two-year warranty on the road reconstruction that accompanies this phase of the project “to make sure we have mitigated any kind of potential issues into the future,” Koza says. The length of the warranty is more than what the city usually requires.

So far, one of the biggest challenges facing the project has been its location. All of the work takes place in an environmentally-sensitive area, requiring the involvement from different levels of government, Koza explains. It also means taking particular care while work takes place to make sure “we don’t impact the adjacent environmentally-sensitive areas.”

Next, the forcemain will be installed, says Koza, noting estimating the tender for this work will close in mid-April and the contract awarded in May.

No date has yet been set for the last phase of the project – building the Wonderland pumping station – but the goal is to have the contract for that one dealt with this summer, he says.

The project is being funded through the city’s capital budget.

Stantec along with Spriet Associates designed the project, Koza says.

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