February 12, 2010

In early December 2009, after several months of work, Priestly completed the demolition of two aged and inadequate process plants at the Oakville Southwest Sewage Treatment Plant.

FOCUS | Waste & wastewater

Challenges abound in rehabilitation of Oakville sewage treatment plant

Process of replacing old units required several system redesigns

DAN O’REILLY

correspondent

A three-year, $60 million rehabilitation project now underway at the Oakville Southwest Sewage Treatment Plant is not considered an expansion.

Nevertheless, it is the most expensive non-development related plant upgrade Halton Region has ever undertaken and it is comprised of a whole set of design and construction challenges for the region, Stantec Consultants, general contractor Kenaidan Contracting, and demolition contractor Priestly Demolition.

In early December 2009, after several months of work, Priestly completed the demolition of two aged and inadequate process plants — or equipment trains — plus digesters and a administration building, as well as rerouting the main sewer line.

Now Kenaidan is in the early stages of building two new equipment trains comprised of primary tanks, settling tanks, secondary treatment plants and other components.

The project also includes the construction of an 8,600-cubic-metre inground equalization tank to temporarily store peak flows during severe storm events as well as the reconstruction of a pumping station.

The new trains are being built to meet existing and anticipated Ministry of Environment wastewater effluent criteria and to address a longstanding problem of wet weather flow control, says Dave Andrews, the region’s director of wastewater.

“The plant has a rated capacity of 45 million litres a day, but has to be able to handle up to five times that flow during extreme wet weather events.”

When the facility was last upgraded in 1977, the Ministry of Environment approved the 45-million-litres-a-day standard. But that flow level was never realized and the old trains that were built in 1955 and 1961 respectively were shut down because of their age and reliability.

“The original plants have remained out of active service for quite a while, only being used for wet weather flow control and holding tanks,” Andrews said.

A number of studies dating back to the late 1990s, however, recommended the structures be replaced because of their age, the condition of the concrete, and their configuration, he explains.

“The region has implemented a phased approach to replace and upgrade the plant’s aged infrastructure.”

Achieving that goal with this current Phase 3 upgrade hasn’t and won’t be easy, though.

Designing a system capable of handling a low- to high-range volume flow took a considerable amount of time with several redesigns, says Andrews.

Then there is the Oakville Sewage Treatment’s location in a residential area just north of Lakeshore Road between the Third and Fourth Lines. For the safety of the contractors and its own operational personnel, a new temporary construction entrance off Lakeshore and new access road around the plant had to be built without impacting a natural tree buffer on the property.

“This was a very tight access. The site has also been set up so Kenaidan’s work is within a construction island (completely fenced area) to delineate the between the construction and non construction areas.”

During the Environmental Assessment, the region made a commitment to the area residents not to impact the tree buffer which is a provincially designated mature woodlot with sensitive varieties of vegetation including a rare and protected butternut tree, says the director.

The province and federal governments will be providing funding up to a maximum of $33 million under the Infrastructure Stimulus Funding program. In order to fast track the project to meet that program’s requirements, the region has pre-purchased and pre-selected major equipment components, says Andrews. He expects the bulk of the civil construction to be completed by the end of March 2011.

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