Water Down the Road: Repairing A Critical Transmission Main While Keeping the Taps Running
John Donald Eisnor, Kevin Healy (Halifax Water)

In June 2023, Halifax Water experienced a failure on a 900 mm prestressed concrete cylinder pipe transmission main. This transmission main is the sole supply to one reservoir and approximately 15,000 customers and could not be taken out of service to complete the repair. The intent of this case study is to discuss the challenges encountered and the solutions used to complete the repair.

The challenges included:

- The inability to take the transmission main out of service under the normal system configuration.

- Maintaining water supply to the downstream communities during the repair.

- An unexpected change in pipe lay direction at the location of the break resulting in a lack of repair pieces.

- Dewatering 3,000 m of transmission main and the resulting regulatory challenge this presented.

- A failed attempt to install a 900 mm line stop to reduce the amount of pipe dewatered.

- Contractual issues with the contractor hired under emergency conditions to complete the repair.

- Scheduling the work around street access requirements established by Nova Scotia Public Works. The innovative solutions included:

- Temporarily stabilizing the failure using steel repair bands and a mass of concrete until a permanent repair solution could be developed.

- Constructing a 200 mm above ground ’“back door’” feed to the zone from a control chamber to a hydrant to increase the length of time the transmission main could be taken out of service.

- Utilizing an experienced pipe contractor to complete the repair.

- With the significant amount of pipe dewatered, a unique and in-depth plan for what would trigger a boil order was prepared and presented to the regulator.

The innovative solutions included:

- Temporarily stabilizing the failure using steel repair bands and a mass of concrete until a permanent repair solution could be developed.

- Constructing a 200 mm above ground ’“back door’” feed to the zone from a control chamber to a hydrant to increase the length of time the transmission main could be taken out of service.

- Utilizing an experienced pipe contractor to complete the repair.

- With the significant amount of pipe dewatered, a unique and in-depth plan for what would trigger a boil order was prepared and presented to the regulator.