Wastewater Treatment systems

The type of wastewater treatment system specified is contingent upon the soil inventory onsite – soils dictate the type of system required.

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Proper soil analyzation is critical to the success of your septic system. A recent publication by Onsite Installer magazine listed the number one cause of failed systems to be improper soil identification. Over the last decade, Daniel has devoted most of his time to studying the soil inventory in most areas of Alberta. This gives customers security that their septic design will be designed correctly for the soils at their sites.

The Maximum depth of a trench is 3 feet. For Primary treated effluent (wastewater from a septic tank) the code requires a minimum of 5 feet of suitable soil below trench bottom to effectively treat the effluent. For Secondary treated effluent (from a treatment plant or a mound) the code requires at least 3 feet of suitable soil below trench bottom to treat the effluent. In cases where there is approximately 3 feet of soil or less, as measured from native ground surface to a restrictive layer a pressurized sand treatment mound is typically prescribed.

For further information view the Alberta Municipal Affairs website: Homeowner Information - Advice for Selecting a Private Sewage System.

Primary Treated Effluent Systems

This type of septic system comprises a conventional two compartment septic tank and a septic field.

The sewage from the home travels through the plumbing of the facility and enters the first compartment of the septic tank. This is where the solids within the wastewater are allowed to settle to the bottom of the tank (sludge) and the greases and soap residual can float to the top of the wastewater and creates a scum layer. This first compartment of the septic tank is crucial to being sized correctly for the facility so that there is sufficient retention time to allow the solids to settle and greases to float. Physical separation is the only treatment process that occurs in the first compartment of a septic tank. Very limited biological digestion occurs in the septic tank, as it is an anaerobic environment. This compartment needs to hold the expected volume of wastewater from the home for a minimum of 24 hours to allow the settling/floating process to occur, to protect the soils from becoming plugged with solids and grease.

At this time Alberta requires ALL wastewater from homes to be sent to a holding tank or septic tank. There is no differentiation between black water (toilet water) and grey water (laundry/shower water). Although grey water contains less solid waste than black water; it still contains viruses, and bacteria that can pose a human health risk.

Typical Cross Section - Tank Details

The middle section of the working chamber contains the cleanest effluent. The effluent travels downstream to the second compartment (dose chamber/tank) for further settling and to be contained until a specific volume can be dosed out to the soil based treatment area. Once the wastewater from the home has been retained for a minimum 24 hours, it is considered to be primary treated effluent. Final treatment of the effluent takes place in the soils.

Primary treated effluent can be distributed to the soils via a trench type system when the site and soil conditions at the site allow. This includes traditional pipe and washed drain media type systems and chambers (plastic domes) as well. The distribution of the effluent can be either by gravity or pressure distribution. Pressure distribution is highly recommended as it ensures all of the usable soil inventory receives wastewater each time the pump cycles. Another benefit is the trench bottom area may be reduced as the code allows loading rate factors if pressure distribution is incorporated into the design and provided the soils can have an increased loading rate.

  • ~50% settlement of total suspended solids with wastewater stream. The remainder of the solids(organics) ends up being deposited in the soil based treatment area via the effluent.
  • Can be distributed by siphon to pipe + washed drain media or chamber type trench systems.
  • Can be distributed with a pump + pressurized distribution laterals in order to utilize entire treatment area.

Secondary Treated Effluent

Various manufacturers have treatment plants that treat the sewage prior to discharging it into the soil based treatment area. Secondary treated effluent is of a higher quality than primary effluent. This means it contains less solid matter and less organics, and therefore reduces treatment demands on the soils. Some types of soils require secondary treated effluent only. The two major types of treatment plants are as follows:

  • Aeration only – these types of systems provide an increased amount of oxygen to the wastewater to encourage the development of aerobic bacteria to digest organics within the sewage.
  • Aeration + Attached Growth – these types of systems have media within the tank for the aerobic bacteria to attach to so they can digest the organics within the sewage.
  • Secondary treatment systems are useful when there is less than 5 feet of suitable soil for the effluent to travel through. Although secondary treated effluent is a much higher quality when compared to primary treated effluent, a minimum of 3 feet of suitable soil for the effluent to travel through for final treatment is still required.

* ALL Secondary treated effluent requires pressure distribution + timed dosing with data logging capabilities. Examples of various secondary treatment plants available in Alberta can be provided by D&S upon request.

  • Treatment fields (both primary and secondary) are required to be seeded to lawn.
  • The field area is to receive regular lawn care maintenance to ensure maximum aeration of the soils, while keeping compaction to a minimum.
  • The designer is to be consulted regarding placement of trees near the treatment system area.
  • Small ride on lawn maintenance equipment is permitted to drive on the treatment field area
  • The treatment field area should be inspected regularly for tunneling or burrowing rodents. Rodent control is required to prevent any extensive damage to the treatment system. This is the responsibility of the property owner.

Sand Treatment Mound


  • Useful in high water or shallow restrictive soil layer conditions.
  • Primary treated effluent can be pressure distributed to a minimum 12” layer of washed concrete sand (sand specifications must achieve the requirements of the code). Once the effluent travels through the sand, it is considered to be similar to secondary treated effluent.
  • These systems are constructed on existing native ground. And require all materials to be imported to construct the above ground mound.
  • Mounds are typically between 3 or 4 feet above native soil.
  • Side slopes of the mound are minimum 1:3.

Finished sand treatment mound

Finished Sand Treatment Mound
(The mound is just in front of the row of trees)
  • Mounds can easily be incorporated into the final landscape plans for the property
  • Placement of the mound can provide privacy and windbreaks for the home
  • Consultation with the designer is required to determine placement of suitable vegetation and approximate setback distances for trees
  • Mounds are to be seeded to grass, and are to be treated as part of the lawn. This requires mowing on a regular basis to allow for maximum aeration of the soils.
  • Small ride on lawn maintenance equipment is permitted to drive on the mound.
  • The mound area should be inspected regularly for tunneling or burrowing rodents. Rodent control is required to prevent any extensive damage to the mound. This is the responsibility of the property owner.


A finished sand treatment mound. Here the landscaper has included some rock gardens and trees to tie the treatment mound into the final landscape design.

LFH At-grade Treatment System

  • All LFH At-grades require secondary treated effluent and are to be installed in a forested area
  • Pressure distribution laterals are placed on pipe supports just above the forest floor and then covered with chambers and bark mulch for insulation.
  • Any trees that may require removal, are to be cut off at ground surface and the stump is to remain in the ground.
  • The LFH horizon is not be compacted with machinery or stripped.
  • Soils are not to be imported as in the installation of a treatment mound.
  • This is the only treatment system that requires the mandatory use of open bottomed chambers.
  • The bark mulch imported to cover the system is to be suitable to the ecology of the forest. Care is to be taken to ensure that any harmful species of “bugs” that could be detrimental to a forest are not imported.
  • These systems can require additional bark mulch to added over time to ensure that the system is properly insulated.
  • LFH At-grade also require regular inspection to ensure any burrowing rodents are not causing any issues with the system operation.
  • In some instances, existing wildlife in the forest can trample the system and sometimes require repairs.
  • Damage from wildlife in the forests cannot be predicted, it is a fact of country living.

LFH At-grade septic fields
LFH At-grade septic field installation. Photo compliments of Gray line Contracting Ltd

LFH At-grades during and after constructions
LFH At-grade during and after construction... nicely blended into the landscape. Photo compliments of Alaqua Projects Inc.

Learn more...

  • The Forest Floor website
    Since humus forms are comprised of a group of soil horizons located at or near the surface, which have formed from organic residues (separate from or mixed with ... There are two groups of organic horizons– those that are formed in relatively well-drained conditions (LFH) and those that are formed in poorly drained... more

  • Top Spray Services Video
    Bark Mulch application to an LFH At-grade... view

Requirements of ALL Wastewater/Septic Systems in Alberta

  • Mandatory minimum two soil profiles to be completed for each site (with the exception of a surface discharge system – which only requires a single soil profile investigation)
  • Soil samples to be collected from the most limiting layer for design
  • Mandatory texture by hydrometer testing by a certified lab for collected soil samples
  • GPS coordinates for soil profiles
  • ALL systems within Alberta MUST have a filter. The simplest filter follows a pump; as this type is self-cleaning each time the pump cycles.
  • ALL systems within Alberta require a high water alarm.
  • ALL systems also require monitoring ports.