Milliken Reservoir & Pump Station

A $90-million expansion of the Milliken Reservoir and Pump Station in York Region north of Toronto is under way. The expansion is doubling the size of the facility in order to help meet the future drinking water needs of the city of Toronto and York Region.

Owned and operated by the City of Toronto, and one of three major reservoirs north of the city, the existing Milliken in-ground reservoir was built in the 1970s and receives water from Lake Ontario. Associated Engineering is providing engineering design and construction administration services for the expansion, which will increase the storage capacity of the reservoir and its pumping capacity, and will provide stand-by power to the existing Milliken facilities

The project is a huge undertaking. The existing two-cell reservoir has a combined capacity of 134 million litres. The new reservoir, being built adjacent to the existing reservoir, will double the capacity to 268 million litres. The underground chamber is made of steel-reinforced concrete covering an area of 16,800 square metres and supported on 446 columns, 9 metres high. On its roof will be placed 400 mm of overburden and topsoil to provide soccer fields for the town of Markham.

Approximately 1,100 metres of large diameter watermain and six new valve chambers were required to be constructed on-site to service the expanded facility.

The new pump station adds three 90 ML per day and three 45 ML per day pumps, with ancillary electrical and mechanical equipment. Selecting the appropriate pumping units was a design challenge. The units needed to convey today’s flows efficiently, yet they had to be sized to accommodate pumping requirements to the year 2031. With input from the city’s operations staff, the design team developed the solution of combining the different pump capacities, installing fixed and variable speed drives, and recommending flexible operating strategies.

The site conditions required the engineers to do a sophisticated structural analysis of potential seismic scenarios. The result is believed to be one of the first “post-disaster structures” constructed by Toronto. Special connections were required to be designed at each entry and exit to the structure. The connections had to provide flexibility in the event of an earthquake, yet retain the integrity of the piping system. Each connection was custom engineered, fabricated and installed.

To minimize dead zones in the reservoir cells and ensure efficient disinfection, a new access house was constructed with connections between the existing and new reservoir cells in order to encourage water circulation. In addition, curtain walls were placed in the cells to better facilitate water flow.

On the operational side, the city required that water storage and pumping at the plant was uninterrupted during the construction. The construction schedule was aggressive and the contractor employed significant resources and innovative techniques. Special column forms were developed and used to allow construction of the 446 columns to proceed more efficiently. Also, to allow for the base slab to be placed during winter months, a glycol heating system was installed underneath the slab to maintain proper placement temperatures.

The timely delivery of shop drawings and shop drawing reviews, as well as equipment testing and delivery to the site had to be carefully coordinated. For example, as the pump station was being constructed, the bridge crane was installed in the building, prior to the roof being placed. This crane was then used to place the new pumps into position.

Construction began in the summer of 2009 and the pumping station was operational in April this year. The reservoir cells will be in service this summer. The project also involves upgrades and remedial work in the existing pump station and reservoir, which is expected to be completed by mid-2012. Careful coordination is required between Associated Engineering, the contractor and the city operations in shutting down the existing facilities and delivering water using the new pump station and reservoir.

The success of the Milliken project to date has been achieved through teamwork and communication between the client, engineers, contractor and subcontractors. In particular, having a full-time project manager on-site has enabled the consultant team to be more intimately engaged with project matters. They can quickly resolve most day-to-day construction matters and, at the same time, be more proactive in overall project management, both of which have aided the project delivery. cce

Bondfield Construction Associated Engineering (Chris Caers, P.Eng., Bill De Angelis, P.Eng., Rick Swinton, Krys Pioro, P.Eng., Frank Dolling, P.Eng., Rada Djunisijevic, P.Eng., Mike Dupre, Patrick Zhao, P.Eng., Paul Shi, P.Eng., Caroline Korn, P.Eng.)City of Toronto