Going with the Flow: A case study

Thursday, May 23, 2019

It was a water main replacement that pushed M & E Engineering to dig deep within its expertise to bring relief to a Southern Ontario neighbourhood. Conducted over a span of two years, the $350,000 project tasked the mechanical engineering consulting firm with installing a new underground water main for an aging town home complex in Scarborough.

“The existing underground water main was cast iron and had come to the end of its expected service life,” recalls Ed Porasz, P.Eng., President of M & E Engineering. “Due to its condition, the complex was experiencing frequent water main leaks which were creating sinkholes on the driveway and leading to all kinds of headaches for the property owners.

Each sinkhole required a call to an underground plumbing and excavator. It also meant shutting down the main water main interrupting the water supply to all of the suites.

“Each of those emergency repair calls cost over $30,000,” explained Nick Jackson, Project Engineer and Associate with M & E. “And those costs were adding up.”

Going underground

On paper, the job was a straightforward replacement of an aging townhouse water main. Yet as anyone in the industry knows, underground infrastructure work is rarely cut and dry.

The town home complex was comprised of 50 town home units split between nine groups. Each group is supplied with domestic cold water through its own dedicated water service; however, shutting off water for one group meant cutting water supply for other homes.

“This used to be a standard design practice for the age of the site,” explains Jackson. “In our design, we had to allow for a temporary service to each home to prevent continual service disruptions to the other units in the same block when the water was turned off.”

Jackson adds Inoperable service shutoff valves also posed a challenge for the team.

Down to work

M & E Engineering worked with the complex’s property manager to scope the project and determine a solution that would best fit their objectives and budget. A decision was made to conduct full pipe replacement with tendering the project to a number of contractors. A contractor was then selected to carry out the project.

The replacement took place over two phases in Fall 2016 and fall of 2018. First, the contractor installed temporary branch services to a block of town homes to keep the water flowing for residents while they worked to replace the piping was underway. The project took a little longer than expected due to poor soil conditions.

The existing water main was then isolated from the city water main. Next, crews installed new service lines and isolation valves to each home, opting to reuse the existing copper branch from the isolation valve to the homes to reduce construction costs.

“The existing underground water piping was in poor condition, which is typically the case whenever the anodes on the existing steel piping are no longer present,” explains Jackson.

In its place, crews installed new municipal grade potable water PVC piping, which was then pressure tested to ensure no leaks were present. After cleaning and chlorinating the piping, and testing a water sample, the trench was closed and the property manager moved forward with their own plans to resurface the driveway.

Lessons learned

Underground work can be both be complex and costly. Yet as projects like M & E Engineering’s water main replacement in Scarborough make clear, some upfront consideration can save costs and prevent issues and make the overall project affordable and livable:

  • Water shutdowns: Test city water valves to ensure they are operable before starting a project.
  • Soil conditions: Test the underground soil before starting the project.
  • Safety first: Excavation equipment will block driveways. As such, it is important to safely control the flow of car and pedestrian traffic in the area.
  • Piping before paving: If a site has cast iron underground water mains, replacing the piping should be considered before replacement or major repaires of the asphalt pavement is considered.
  • Temporary water by-passes: Verify whether the site has isolation valves and identify where they are located throughout the complex. This should be investigated to allow the main to be isolated in various sections.

Ed Porasz and Nick Jackson are with M & E Engineering, a professional multi-disciplined mechanical and electrical engineering consulting firm serving clients in the GTA and across Canada. For more, visit www.me-eng.com.

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