The design of the most efficient and cost-effective onsite wastewater treatment system is fundamental to ensure performance, longevity, and protection of the environment. The design of the wastewater system for your property requires site visits, soil testing, assessment of building occupancy and use, and the creation of a site plan.
In planning your system, an installer/planner/designer will likely . . .
- Make a site drawing of your property and evaluate the area available for a wastewater system. He/she will attempt to create a design that preserves the landscaping and natural elements of your property.
- In the site drawing, the installer/planner/designer will show the location of other utilities including your well and the location of any public water adjacent to your property.
- The installer/planner/designer will evaluate the soil conditions of your property to determine its ability to accept wastewater. Under local, provincial or national regulations, the installer/planner/designer has a choice of determining the soil texture using lab tests. In some jurisdictions either a percolation test or a permeameter test may be performed at the treatment site to establish the loading rate. The quality of the domestic water supply will also be considered since sodium, iron and other components of well water are a factor in system design.
- The installer/planner/designer will ask you to supply information on the size and use of the structure in existence or to be built. In the case of a residence, the number of bedrooms and the expected occupancy will be a factor in design. If the home has jetted tubs, large appliances and/ or will be used for a home-based business, the capacity to accept the additional wastewater will be designed into the system.
- The designer will establish a peak daily flow rate expressed in gallons or litres per day the system must be able to handle. The flow rate must meet or exceed the minimum standard specified by the provincial regulatory framework.
After completing the tasks above, the installer/planner/designer will recommend one or more systems suitable for your property based on the flow rate, the land area available, the soil conditions and the presence of adjacent public water.
The installer or designer must submit a system design that meets or exceeds the requirements of the provincial regulations in order to obtain a permit from the permitting authority prior to construction. In most jurisdictions an inspection of the system is required prior to completion. There are five types of systems commonly in use in Western Canada. They are:
- Tank and field
- Tank and mound
- Advanced treatment plant
- Open Discharge (also called Ejector systems) (not permitted in BC)
- Advanced treatment and at-grade (not permitted in BC)
Tank and field
Standard soil-based treatment systems use a septic tank for initial treatment. The household plumbing collects wastewater and sends it to the septic tank which acts as a separation chamber. Heavy particles separate from the wastewater and settle to the bottom to form a sludge layer. Lighter particles, mainly soap, grease and toilet tissue separate and float to the top to form a scum layer. Using a baffle device the clearest liquid from the center of the tank flows by gravity to the effluent dosing chamber. A pump or siphon in the effluent dosing chamber will deliver the effluent to the final soil treatment component, in this case the septic field.
Tank and sand mound
As discussed above, the household plumbing collects the wastewater and sends it to the septic tank where it is separated into the three layers, sludge, scum and wastewater. Once the wastewater enters the effluent dosing chamber of the septic tank, the pump in the effluent dosing chamber delivers the effluent to the mound system. In a mound, pressure distribution pipes are placed in a bed of aggregates or chambers with a 12” layer of sand below. The wastewater is pumped into the pressure distribution system and sprays into the sand layer, where aerobic bacteria cleans the water. A sand mound receiving primary treated effluent (Type 1) must be above ground and must have a separation of three feet (AB, SK & MB) or two feet (BC) between the bottom of the sand layer and a restrictive layer or water table. Sand mounds receiving secondary treated effluent (Type 2) may have a reduced sand layer depending upon the regulatory requirements in the jurisdiction in which it is installed. Mounds must be landscaped with grass and be regularly maintained in order to have improved efficiency.
Advanced Treatment Plant
Other options for initial treatment components are manufactured packaged sewage treatment plants. They may have components, such as textile filter systems and aeration devices. These components, like a septic tank, will receive all the wastewater generated by the facility they serve. These systems will produce cleaner effluent and are considered to be advanced treatment systems. Cleaner effluent increases the percolation rate of effluent through soil pore spaces during the final treatment component.
Open Discharge or Ejector Systems (not permitted in BC)
Open discharge systems are sometimes used on farms or acreages. In this system waste enters the septic tank and the wastewater is discharged through a pipe system onto the open property. There are strict provincial guidelines on size of property required to run a direct or open discharge as the discharge must occur a certain distance from the property line and any water source on the property or within a certain radius of the discharge. Refer to the regulations for the jurisdiction the system is located in to obtain information on the requirements and restrictions regarding open discharge systems.
Advanced Treatment and At Grade (not permitted in BC)
The At-Grade effluent treatment and disposal system is a method of accomplishing the final treatment and disposal of effluent from an advanced sewage treatment plant. The At-Grade is arranged utilizing pressurized distributional laterals above virgin ground surface. The pressurized pipe is supported 1 ½ inches above ground surface utilizing feet spaced every meter along the length of the pipe. The pressurized lateral is then covered with a 4 – 6 inch insulated shield. The entire assembly is then covered with wood chip cover or leaf mold or peat moss. The width will vary between 3 and 6 feet depending on slope and terrain variables.
Freezing is avoided by adequate cover, proper timed dosing, and proper drainage of pipes. All of these parameters are site specific and require specialized training to accomplish this task. At-grade systems are not allowed in all jurisdictions and may require a variance for installation.
A typical At-Grade will perform at a rate 4.3 times better than any subsoil absorption method. Within 2 – 6 years, the entire area of the At-Grade will become infiltrated by local flora and fauna, blending it in with the surrounding terrain. The efficiency of the At-Grade is expected to improve as time passes, decomposition and growth in the area aid in the absorption/distribution of water. Research indicates that At-Grades out perform all other methods of final treatment in high water table areas and tight clay soils.
At-Grades perform best in treed areas where protection from wind and vehicles is greatest. The vegetation in the forest provides the best infiltration available. Areas with sloping terrain are preferred, but level areas are also acceptable.
Understanding Your New Wastewater Treatment System
Your system safely treats wastewater and returns it to the ground. After installation and inspection, the safe operation and regular maintenance of your OWTS are your responsibility. Your system is more than a simple tank – it is a utility and our homeowner’s manual will help you understand and operate it.