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Water Supply and Sewage Systems in the North

Technical Series 94-218
Key Messages
  • Both water supply and wastewater systems may be on a storage tank basis or piped system.
  • Tank systems are generally less expensive to install but require regular maintenance by the householder.
  • This factsheet provides best practice for system installation to provide for
    • freeze protection
    • overflow protection
    • alarm systems
  • Venting plumbing systems is particularly troublesome in the North. Best practice methods are described which prevent freezing and blockage of the vent pipe and consequent backup of sewer gases into the house.
Water Supply

Water Tanks

In communities where piped water is not available, each house is equipped with a storage tank made of steel, aluminum, polyethylene or fibreglass. Tanks must be located inside the heated envelope. Domestic water is delivered in the form of ice blocks or liquid that is trucked in from a central supply point.

Tanks are equipped with removable covers or have exterior pipes which are connected to the truck for filling. The water may be gravity fed or pumped. These systems usually have an overflow pipe to allow air to escape and to indicate when the tank is full.

Tank capacities vary. A 1135 L tank is usually large enough for a single family dwelling if water is delivered daily. Larger tanks (up to about 2270 L) should be considered if the water is delivered less often, or to provide additional capacity for times when water cannot be delivered due to storms.

This type of system is less expensive to install than a piped system; the major cost is the tank and its transportation. Tanks must be able to fit through the doors of the house, and the floor must be designed to take the load. Things to note with this type of system include the following.
  • Pressure pumps and controls need maintenance.
  • Tanks must be cleaned out periodically.
  • Overflow pipes tend to freeze in cold weather; it is suggested that they be copper or polyethylene, be insulated, and protrude outside the building envelope as little as possible.
  • A low water cut-off switch should be installed in the tanks to prevent the pump from burning out if the water supply in the tank is depleted.

Piped Water

In communities that have piped systems, water and sewer pipes are carried in insulated and heated Autilidors@, either above ground or set into the ground. The same general design is used whether the system is buried or not. If the system is installed above ground, an exterior protective jacket of material such as steel is used. The advantage of above ground systems is that the piping is easily accessible for repair or replacement. Aesthetically, however, above-ground systems are not very appealing.

The water is usually supplied by means of a two-pipe system (one pipe for supply and one pipe for return) using continuous pressurized circulation which helps to prevent freezing. In the pumphouse the water is continuously heated, usually by waste heat from the electric power station. Some lines that may be more vulnerable to freezing are installed with heat tracing cables. Inside the home, the pipes may be connected to a small, electric circulating pump which runs constantly. Normally water supply and recirculation lines are installed in a 100 mm insulated pipe duct insulated and protected with a polyethylene jacket (Figure 1).

Figure 1: Water Supply Lines
Figure 1: Water Supply Lines. Enlarged Image

Some items to note with this type of system are described below.

  • The connection of the water service to the water main can be more expensive than the rest of the domestic water system and must be performed with a high degree of expertise.
  • Heat tape is more expensive to install and operate than low voltage impedance heat tracing.
  • Polyethylene pipe is typically used in these systems. It has a greater capacity than most other types of pipe to freeze and thaw without rupturing.

In addition to the circulation and heat tracing mentioned previously, there are a number of other methods of preventing freezing in the system.

  • The lines are insulated, usually with 50-75 mm of polystyrene.
  • A flow switch can be installed in the circuit to sound an alarm if the flow ceases and to control the heat tape.
  • Hot and cold water piping should be run with a definite slope and be fitted with valves at the low points to facilitate draining the water systems if the house is to be left unoccupied.
  • If a sloped run cannot be conveniently arranged, an automatic vacuum relief valve can be installed to drain low spots in piping.
  • A freeze alarm can be connected to a central community monitoring service.
  • A drain valve system can be fitted to the water system to automatically drain the pipes upon detecting a drop in temperature.
  • The pressure of the moving water in the town main can be used to force continuous circulation through the pipes to the house.

Wastewater Systems

Piped wastewater systems are preferred over storage systems mainly because of convenience. However, in communities where municipal sewer is not available, sewage has to be temporarily stored until it is removed by truck to a dump site or other point of discharge. The following are the most common wastewater sytsems.

Sewage Storage Tank

The most satisfactory alternative to a municipal sewer connection is a storage tank. The sewage can be pumped out periodically and trucked to a treatment plant.

A sealed tank of rust proofed metal, polyethylene, or fibreglass is connected to the lowest point of the main house sewer. The tanks may be installed either within the heated building envelope (the most common and recommended), within a heated compartment separate from the house, in a non-heated container (not recommended), or underground. The tank should have a larger capacity (preferably 1.5 times) than the fresh water storage tank. Some installations require two or more tanks joined together. A suction pipe enables a sewage truck with a suction pump to empty the tank. Some installations have a high level switch in the tank which can either activate an alarm or disconnect the domestic water pump.

In a gravity draining system, the most satisfactory location for the tank is an insulated compartment under the floor (Figure 2). Gravity draining to the tank is possible in a multi-storey house if all the plumbing fixtures are on the upper floors. Where fixtures are installed below the top of the tank, a lift pump is needed.

Figure 2: Tank in Heated Envelope
Figure 3: Tank in Heated Envelope. Enlarged Image

Items to note with this type of sewage system include the following.

  • Tanks must be pumped out on a regular basis.
  • Pipes must be designed to accommodate the powerful motor of the sewage pumpout truck.
  • Underground tanks have been known to float out of the ground and must be properly anchored against uplift.
  • Alarms can be installed to notify occupants when the heating of the compartment fails.
  • Sewage storage tanks should be sealed and equipped with gasketed, bolted manholes and covers for maintenance and repairs.

Venting Problems

Plumbing vents are a source of trouble and inconvenience in the North. The vent is connected to a sewage tank of substantial surface area, containing relatively warm water producing large amounts of vapour. This vapour condenses and freezes in the pipe, causing complete blockage. Sewer gases then bubble back through the fixture traps into the house. To avoid these problems, it is suggested that:

  • the vent pass through as little unheated space as possible,
  • the vent termination be exactly 25 mm from the roof,
  • the vent termination (including portions of the vent that run through unheated space) be insulated with at least 50 mm of insulation, and
  • all connections of the vent stack be located in heated space.

If the run through unheated space is not too long, copper pipe can be used for the termination. It should extend at least 3 m into the heated space. The copper conducts enough heat to the tip to prevent freezing of the vapour. A heat trace can be used to keep the vent open but this requires maintenance and uses electricity. Its use should be limited to clearing a frozen vent.

Utilidors

The sewer lines are usually installed in the same utilidor as the water supply and insulated and protected in the same way. Skilled tradesmen are required for the installation of the sewer main and to make the house connections.

Apart from the use of insulated polyethylene pipes, sewer connections to utilidors are of conventional design. A much steeper slope is required than in southern systems to prevent the build-up of ice.

If the pipe freezes, it can be thawed with a steamer (portable steam generator) or a thaw tube (flexible plastic tube that uses hot water under pressure to drill through the ice). Access should be provided to thaw the pipe or to clear a blockage.

If it is necessary to lift sewage and wastewater to the sewer main, a sewage storage tank can be installed similar to those discussed above and fitted with a lift pump. A float-controlled switch automatically starts the pump when the storage tank is full and shuts it off when the sewage level falls to its operating minimum. To prevent freezing between cycles, there should be no check valve in the pressure pipe from the pump so that when the pump shuts off any liquid remaining in the pipe can drain back into the tan. The normal capacity of a domestic sewage storage tank with a lift system is about 135 L but this should be increased by an amount at least equal to the volume of the pipe from the pump to the sewer main.

Other Systems

References

Design Guidelines and Technology for Northern Housing Construction, April 1983, Indian and Northern Affairs Canada, Technical Service and Contracts, Section 8.

Examples of Housing Construction in the North, by Burdett-Moulton, Architects and Engineers, Northwest Territories, Don Jossa and Associates, Yellowknife, Northwest Territories, and Wayne Wilkinson, Consultant, Whitehorse, Yukon; for Canada Mortgage and Housing Corporation; April 1987.

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