Pressure is mounting to better manage rural septic systems, so know the fundamentals of sewage treatment, starting with the soil
Most landowners want a septic system that's up to the job. In fact it would appear many farmers and ranchers harbour some concerns in that department. Household wastewater management ranks among the top five environmental challenges for producers who have completed an Environmental Farm Plan (EFP).
In Alberta, standards for the design, installation and material requirements of on-site private sewage treatment systems are set out in the Alberta Private Sewage Systems Standard of Practice under the Safety Codes Act. However, standards are just part of a bigger picture that involves designing the right kind of sewage treatment system, says Joe Petryk, senior field inspector for Alberta Municipal Affairs, a man who has dealt with these issues for many years.
"Any system is as unique as the site it serves," he says. "Soil suitability, land gradients, lifestyle and the number of people living on the property are all factors to consider when deciding the kind of system to install. The site's capability to treat wastewater is a combination of its ability to accept the wastewater load, meet separation distances to other site features, and have the depth of suitable soil needed to achieve treatment.
"Knowing the details of your system design is a major factor in the extent and type of maintenance that needs to be done."
A good starting point to address household wastewater management and a host of other environmental issues on a farm or ranch is to develop an EFP, says Petryk. Developing an EFP is an excellent process for understanding and assessing the risks of various approaches to farm sewage treatment systems from a human health and groundwater protection perspective.
One of the most important decisions when developing a septic system is deciding how wastewater reaches its intended destination. Gravity-fed and pressure-fed systems are the two common design choices, with pressure-fed generally preferred.
"There are two types of gravity-fed systems," says Petryk. "The first has the effluent pumped from the effluent chamber of the septic tank to a distribution box where gravity then distributes the effluent through a series of lateral pipes. The effluent is then absorbed by the infiltration area within the treatment field trenches.
"The second has the effluent flow directly out of the effluent chamber of the septic tank and into a lower-elevation treatment field. The effluent is distributed underground through a series of lateral pipes which allows it to be absorbed by the infiltration area within the treatment field trenches. This is commonly referred to as a trickle system and not generally recommended. Gravity-fed systems have the potential to overload parts of the treatment field and not load other parts of the field adequately thus allowing for ineffective sewage treatment.
"Pressure-fed systems use a pump set in the effluent chamber of the septic tank that forces the effluent throughout lateral piping, distributing the effluent evenly throughout the field. Pressure-fed systems are generally recommended because the effluent is distributed evenly."
Adequate septic tank size is crucial, says Petryk. Working capacity (first chamber) of a septic tank is based on the number of bedrooms. Additional volumes must be considered and added to the tank size when the predetermined fixture count is exceeded. The Standard of Practice, which should be consulted to ensure all considerations are made with regards to septic tank sizing.
Contrary to popular thought, the treatment of wastewater does not only occur in the septic tank. The majority of treatment will occur in the final treatment component of the system which is usually soil based such as a Treatment Field or Treatment Mound. The septic tank provides only the initial stage of treatment through the process of settling and separation of solids.
The treatment system depends largely on soil type, says Petryk. The Standard of Practice requires a site evaluation, with test pits dug to produce a soil profile. A soil sample of the most limiting condition within the proposed treatment zone are collected and sent to a laboratory for analysis to determine texture. Soil texture classification determines the effluent soil loading rates for the treatment system design.
Percolation test results are now only being used in support of a design that is based on a soil profile investigation and a site evaluation required by the Standard.
Holding tanks. In some instances, when a site is faced with several design constraints the only option may be to install a holding tank. Available in various sizes sewage then needs to be removed from the tank by a vacuum truck and disposed of at an approved disposal site, usually a municipal lagoon. Water tight septic tanks or sewage holding tanks must be no less than:
Open discharge. The design and location of an open discharge system that discharges effluent onto the surface of the ground must ensure the effluent is contained on the property. These can be the easiest septic systems to maintain, says Petryk. "If a landowner already has this type of septic tank system, then management largely involves keeping track of solid waste build-up and deciding how often to vacuum out the first chamber of the septic tank."
Open discharge sewage systems must be no less than:
Treatment fields. These are subsurface fields to which wastewater is discharged and the aerobic treatment of wastewater takes place. Soil characteristics will dictate the size and design of the treatment field.
Subsurface treatment fields must be no less than:
Treatment mounds. Petryk says treatment mounds, built on top of the existing landscape, are used where it is difficult to achieve the required vertical separation from the infiltrative soil interface to the limiting condition below it.
It is important to keep all types of traffic off a mound and maintain the grass growth over the entire mound. It is also important to divert runoff water away from the mound. Whenever treatment mounds are built on a slope, a diversion should be constructed upslope of the upper side of the mound berm to intercept and divert runoff water away from the mound.
Treatment mounds must be no less than:
Lagoons require large land parcel sizes. "Because lagoons are meant to retain effluent, the sides and bottom of the lagoon are constructed in soil with high clay content or with a synthetic liner to prevent the effluent from leaching out of the lagoon. The intent is to have effluent evaporate."
Maintenance of lagoons involves monitoring the collection pit at the bottom of the lagoon to make sure the solid waste isn't building up too high. "Lagoons generally do not require a lot of maintenance. The main things to do are to fence the lagoon to prevent access to animals and humans , maintain grass and weed growth on the berms, and divert surface runoff away from the lagoon," says Petryk.
An evaporative lagoon serving a single family dwelling or duplex can not be located within:
An evaporative lagoon serving other than a single family dwelling or duplex can not be located within:
For more information on septic systems, including maintenance tips, visit the Alberta Municipal Affairs Web site at www.municipalaffairs.gov.ab.ca/ss_index.htm or call toll-free 1-866-421-6929. Another resource is the Alberta Onsite Wastewater Management Association (AOWMA). Visit the AOWMA Web site at www.aowma.com.
More information on EFPs in Alberta is available at www.albertaefp.com.