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June 14, 2006
feature article

Farm septic systems — knowing the basics

Knowledge of the land key to developing a safe and efficient septic system

Truck Producers are assessing their household wastewater management through the completion of an Environmental Farm Plan.

The average farm septic system is the sometimes-neglected workhorse of the farm. According to Alberta Municipal Affairs, the average person puts 340 litres of sewage through a septic system every day. For a family of four living in a two-bedroom house, that amounts to 1,360 litres per day and just under half a million litres per year.

With that kind of workload, most landowners want to develop a system that's up to the job. And it's evident that septic system issues are very much on the minds of Alberta producers — an ongoing survey reveals that household wastewater management ranks among the top five environmental challenges producers who have completed an Environmental Farm Plan (EFP) consider fundamental to the sustainability of their farms and ranches.

In Alberta, standards for the design, installation and material requirements of on-site private sewage systems are provided by the Private Sewage Systems Standards of Practice under the Safety Codes Act. However, standards are just part of a bigger picture that involves tailoring the right kind of septic system to your land, says Joe Petryk, senior field inspector for Alberta Municipal Affairs.

"Any given septic system is as unique as the land it services," says Petryk. "Soil quality, land gradients and the number of people living on the property are all factors to consider when deciding the kind of septic system to install. Also, knowing the details of your existing system is a major factor in deciding what kind of maintenance needs to be done."

One way to address household wastewater management and a host of other environmental issues on a farm or ranch is to develop an Environmental Farm Plan (EFP). An EFP is a free, voluntary assessment of an agricultural operation's environmental strengths and weaknesses.

Pressure vs. gravity

One of the most important decisions when developing a septic system is deciding how wastewater reaches its intended destination. Pressure-fed and gravity-fed systems are the two common choices where it comes to septic system discharge.

"Gravity-fed systems are fairly self-explanatory," says Petryk. "The sewage flows out of the tank and into a lower-elevation field, which takes the effluent underground through a series of pipes and allows it to be absorbed by the infiltration area within the field.

"Pressure-fed systems, meanwhile, use a pump set in the effluent chamber that forces the effluent into the treatment field, distributing it evenly throughout the field. We generally recommend pressure-fed systems because of this; the effluent doesn't mass in one place like it sometimes does in gravity-fed systems."

Tank size matters

Making sure the septic tank size is adequate for the farm's needs is a crucial consideration when installing a septic system, says Petryk. A septic tank that is too small to meet the needs of those living on the farm can cause unwanted problems.

Although there are several factors to consider when deciding on the size of a septic tank, Petryk says an estimate of a household's required capacity can be calculated using a simple formula.

"In single family dwellings, the average volume of sewage per day is estimated at 340 litres per person," he says. "To get a general idea of the size of tank required, multiply the number of bedrooms by the number of people per bedroom and then multiply the result by 340. For example, two persons in a two bedroom home would be two multiplied by two multiplied by 340 to equal the number of litres required."

Treatment systems

Contrary to popular thought, the purification of wastewater does not take place within the septic tank. Rather, the aerobic process which purifies the water occurs in a field or treatment mound before being returned to groundwater.

Making the right decision on what kind of treatment system to use depends to a large degree on the type of soil profile the property has to offer, says Petryk. Currently, the Private Sewage Standard of Practice accepts a "soils percolation test" or a "soils particle or grain size analysis test" done by a lab to arrive at the acceptable effluent loading rate of a field or mound. Of the two, the latter is more accurate, says Petryk.

"The 'perc test' determines the rate at which water is absorbed by the soil after the test hole is saturated. If not done properly, the results can jeopardize the design of the sewage treatment system," he says.

"Meanwhile, the particle or grain size analysis test accurately establishes the amounts of clay; sand and silt in the soil and provides a soil classification to properly design the sewage treatment system. As designs of systems become more critical to prevent system failures, percolation tests are less reliable and the particle or grain size analysis is highly recommended."

Holding tanks. In some instances, when a site is faced with several design constraints the only option may be to install a holding tank. These tanks are available in various sizes and store the sewage until such time the tank is full. The sewage then needs to be removed from the tank by a sewage pump truck and disposed of at an approved disposal site, usually a municipal lagoon. In some cases land spreading is allowed under the approval process established by Alberta Environment.

Water tight septic tanks or sewage holding tanks must be no less than:

Open discharge. These are the easiest septic systems to maintain, says Petryk. "If a landowner already has an existing septic tank system, then management largely involves keeping track of solid waste build-up and deciding how often to pump it out."

Open discharge sewage systems must be no less than:

Subsurface fields. These are underground fields to which wastewater is discharged and the aerobic treatment of wastewater takes place. They are generally most appropriate in loamy soil conditions.

Subsurface treatment fields must be no less than:

Treatment mounds. Petryk says treatment mounds, mounds that are built on top of the existing landscape, are best used in situations where the subsoil is not suitable for absorbing effluent.

However, they are also somewhat high-maintenance. "They have to be protected from animals and traffic and there has to be a good amount of grass and weed control. In the wintertime, traffic, whether it be human, animal or vehicular, can drive frost down through the soil and cause them to freeze up."

Treatment mounds must be no less than:

Lagoons. Lagoons, which retain effluent, are best for land with poor soil. "Because lagoons are meant to retain effluent, the sides and bottom of the lagoon are constructed of compacted clay or a liner is used to prevent the effluent from saturating the soil — the target is to have it 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 off so cattle and humans cannot get into it, maintain grass and weed growth on the berms, and divert surface runoff away from the lagoon," says Petryk.

A sewage lagoon serving a single family dwelling or duplex must be not less than:

More information

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 Private Onsite Wastewater Treatment System Owner's Manual, available from the Alberta Onsite Wastewater Management Association (AOWMA). Visit the AOWMA Web site at www.aowma.com for further details.


The information on this website is available for reprint with credit to "The Alberta Environmental Farm Plan, www.albertaEFP.com".
Article development courtesy of The Alberta Environmental Farm Plan Company

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