Well before the E. coli outbreak tragedy in Walkerton, Ont., in May 2000, the Region of Halton in southwestern Ontario had a history of providing high quality drinking water to its residents.

To maintain its high standard for water quality, the region initiated plans to upgrade its water treatment systems. In 2002, the region retained Associated Engineering (AE) to complete preliminary and detailed design and provide construction administration services for the Oakville (Ont.) Water Purification Plant upgrades. AE has a long history of providing consulting services to the region for this plant, dating back to the 1993 Predesign Report.

The Oakville plant treats 109 million liters per day of water from Lake Ontario. The conventional treatment plant includes alum coagulation, tapered flocculation and sedimentation. Dual-media anthracite/sand filters provide additional particulate removal. Gas chlorination is used for primary and secondary disinfection, zebra mussel control and taste and odor control. Fluoride is also added.

Proposed upgrades will improve primary disinfection, provide better taste and odor control and will consider anticipated near-future regulations, including tighter filter effluent criteria, inactivation of Cryptosporidium oocysts and potential formation of disinfection byproducts.

Upgrades include an Actiflo retrofit in the existing pretreatment facilities. Actiflo, a high-rate, ballasted flocculation, upflow-clarification process, will improve particulate removal. The process ability to accommodate sudden changes in turbidity should benefit the Oakville plant, which is prone to upset during short-term turbidity spikes from storm events.

Completing the upgrades

Ozone will be added for primary disinfection and taste and odor control. The ozone system is designed to achieve 1.0-log inactivation of Cryptosporidium oocysts across all water conditions at all times. Studies confirmed that the ozone upgrades provide a “one-two punch” for effective disinfection under cold water conditions and taste and odor control. Other upgrades include the following:

• Eliminating existing sulfur dioxide system;
• Installing chemical systems including carbon dioxide (pretreatment pH control), sodium hydroxide (corrosion control), hydrogen peroxide (taste and odor control), calcium thiosulphate (ozone quenching and dechlorination), and two polymers (wastewater treatment);
• Upgrading existing high lift pumping stations;
• Constructing a new three million liter treated water reservoir;
• Converting existing Accelerator process wastewater treatment system to a gravity thickener/clarifier process;
• Implementing a dry scrubber for gas chlorine; and
• Developing a preliminary design for an ultraviolet disinfection facility, low lift pumping station upgrade and filter upgrade.

“One of the challenges of this project is developing a clear construction sequencing strategy to allow for timely and cost-effective completion of the upgrades while maintaining the Oakville plant in operation and in regulatory compliance,” said Bill Chisholm, project manager for Associated Engineering. “The region’s project manager, Ron Rae, has been instrumental in coordinating the input from Halton’s Operations and Maintenance and Engineering staff.”

AE emphasized using in-plant space within existing building envelopes as much as possible for the upgrades. The detailed design phase of the $25 million (CAN) upgrade is scheduled for completion as of presstime with construction beginning later in 2004.