Water and Sewer Servicing in Yellowknife, NWT

Water and Sewer Servicing in Yellowknife, NWT

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Water and Sewer Servicing in Yellowknife, NWT Rob Osborne, and Ken Johnson, AECOM October 2012 Servicing a new development, complete with underground water, and sewer is no easy task anywhere in Canada, but the difficulty goes up a notch or two when the ground is solid rock and the construction season is very short. Such is the servicing in Yellowknife, Northwest Territories.

Photo 1. First on the site are the drillers and blasters, whose job it is to reduce the bedrock to a size that is manageable for excavation. The drillers are guided by the survey stakes for the locations, depth, and width of the trenches that they will create. A series of holes are drilled, loaded with a charge, covered with a sufficient number of 5000lb blast mats, and detonated.

Photo 2. KABOOM !

Photo 3. All of the buried pipe is pre-insulated and installed with 300 mm of 25 mm minus crushed rock bedding. The 25 mm minus bedding extends 300 mm above the pipe and the remainder of the trench is backfilled with 50 mm minus crushed rock up to the subgrade of the road.

Photo 4. The installation of services for each house is even more labour intensive than the mains, and each property has one sewer service and two water services. The two insulated water lines, coupled with a circulation pump in each house, protects the homeowner’s lines from freezing. All water service connections include a "goose neck" near the main connection to absorb the expansion and contraction in the service line due to the extreme temperature variation.

Photo 5. The insulation on the water and sewer mains are cut away for the service connections, and reinsulated with a sprayed on urethane foam, and then tarred to prevent water from damaging the insulation. Sections of pipe that are not pre-insulated , such as the bends, and the stubs at the water vaults must also be field insulated and tarred.

Photo 6. The water mains are clamped before and after each bend. The water main also has a copper strip that must be connected with each section of pipe for the corrosion protection of the system. A copper strip is show being welded on at a bend.

Photo 7. To protect hydrant assembles from freezing and damage from ground movement, a concrete vault is built around each hydrant, with enough space to allow access for servicing. Hydrants assembles are design to be “in line” on the water main (hence the two pipes going into the vault) as opposed to the conventional hydrant “tee”, to provide freeze protection from the recirculating water supply system.

Photo 8. The finished hydrant vault is a $45,000 capital investment, but its design and the construction techniques to build them have developed over 30 years in water and sewer work in Yellowknife. Once covered, all that is visible is the hydrant and the manhole cover.

Photo 9. With winter quickly taking hold, there is barely enough time to bring the road up to final grade.

All of the water mains and services are pressure tested and the sewer is camera inspected. As a layer of snow blankets the former job site, there are a few brave individuals already building foundations for their houses.