A private sewage system does much more than make your sewage soak into the ground. The system treats the wastewater to prevent the transmission of disease and prevents damage to the environment. Design, install and operate a private sewage system with care.

The Alberta Private Sewage Systems Standard of Practice 2015 (SOP) provides the performance objectives, design standards, and material requirements for onsite system designs. This standard is available from the Alberta Queen's Printer or phone: 780-427-4952.

Getting the right private sewage system

Prior to the installation, ensure the prospective installer carries a private sewage certificate of competency.

Have the prospective installer:

  • Estimate the expected volume of sewage per day from your home. The estimates in the standard are based on a basic home.
  • Determine the proper size of septic tank, holding tank or packaged sewage treatment plant required for the expected volume of sewage per day.
  • Determine the best location for the system.
  • Establish if a high seasonal water table may cause problems with your system.
  • Confirm clearance requirements from property lines, wells, water sources, water courses, dwellings and others buildings.
  • Identify other systems that may be suitable for your property.
  • Identify the required maintenance for your system, anticipated costs and consequences of failing to maintain it.

During the installation

  1. Ensure the certified installer obtains a private sewage permit before starting the installation.
  2. Watch the installation to become familiar with the design and components, which will help with future maintenance.
  3. Ensure an inspection is conducted and that you receive a copy of all inspection reports.
  4. Ensure the installer provides you with an operation and maintenance manual and reviews its contents with you.

Selecting a new sewage system

Select a system that is properly designed for your needs and complies with the Private Sewage Standard of Practice.

System capacity

Minimum volumes are specified in the standard and are based on the number of bedrooms in a home. If your home has additional features that might increase water use, additional volumes should be included.

If you are building a septic tank system, ensure the tank is large enough for your home.

The minimum septic tank size (working capacity) is specified in the standard:

  • four-bedroom home = 4,260 L (940 gallons)

The size will increase when a garbage grinder is used.

The "Model #" is often NOT the "Working Capacity" of the "Septic Chamber" and cannot be used for sizing purposes. Septic tanks must be labelled and certified to comply with CSA Standards.

System sizing

Determine if the soil-based effluent treatment system (disposal field) is a different size in each proposal you receive from certified installers.

If there is a difference between the sizes of systems proposed, find out why and which is right for you. Ask your installer questions about the design. Some private sewage systems can reduce the soil-based effluent treatment area required as compared to others.

The required size of the effluent treatment system varies depending if the system uses primary treated effluent (septic tank) or secondary treated effluent (package treatment plant, sand filter, mound and other similar systems).

System sizing also depends on how the treated effluent is distributed to the final soil treatment component, such as gravity or pressure distribution.


Another variable is whether the soils are sandy or clay. Clay soil typically has a slow infiltration rate and requires a large soil infiltration area as compared to sandy loam soil.

An investigation needs to determine the texture, structure and grade of the different soil layers, and include a soil sample of the most limiting condition in the soil profile affecting the design.

These characteristics considered together dictate the ability of the soil to absorb and treat the effluent. It is critical to the effectiveness of your system that it be sized for your soil type and the constraints that may exist in the soil:

  • shallow groundwater
  • restrictive soil layers, such as fine-grained clays or coarse-grained sands

Without this information the design of your sewage system will be inadequate and can lead to failure within a couple of years or less.