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Nearly all Rural Properties have some form of septic system to dispose of household waste. The following article taken from CMHC describes the function of a traditional system system and what you should know as you prepare to purchase a farm or rural property.



Understanding Your Septic System

Do you know where the water goes when you empty a sink or flush a toilet? If your home is in a city, the wastewater likely goes into a municipal sanitary sewer system to a sewage treatment plant. If your home is located in a rural area or a small community, you are likely one of the 25 per cent of Canadians whose wastewater is treated by a septic system (also referred to as an onsite wastewater system). A septic system treats your sewage right in your own yard and releases the treated effluent back into the groundwater.

How Does My Septic System Work?

A properly functioning septic system receives all the wastewater created from household use (including toilets, showers, sinks, dishwasher, washing machine, and so on), treats the wastewater to a safe level, and returns the treated effluent to the groundwater system. A conventional septic system is composed of a septic tank and a soil filter called a leaching bed. A leaching bed may also be called a drain field, an absorption field or a tile field.

Septic Tank

The purpose of the septic tank is to separate liquids from solids and to provide some breakdown of organic matter in the wastewater. A septic tank is a buried, watertight container made from concrete, polyethylene or fiberglass. In the past, the tank was sometimes made of steel or wood. If you have a steel tank, it is likely rusted through and needs replacing. If you have a wooden one it is likely rotting and may need replacing. The size of the septic tank will depend upon the size of the house (number of bedrooms) and household water use, with minimum tank volumes ranging from 1,800 to 3,600. Older tanks may be smaller than those installed today and tanks may have one or two compartments, depending upon when and where they were installed.

As wastewater from the house enters the septic tank, its velocity slows allowing heavier solids to settle to the bottom and lighter materials to float to the surface (see Figure 2). The accumulation of settled solids at the bottom of the tank is called “sludge” while the accumulation of lighter solids (greases and fats), which form a mass on the surface, is called “scum”. Anaerobic bacteria, which are always present in wastewater, digest some of the organic solids in the tank. Clarified wastewater in the middle of the tank flows by displacement into the leaching bed for further treatment in the soil layer.

Leaching Bed

The partially treated wastewater from the septic tank flows into the leaching bed (see Figure 3). The leaching bed is typically a network of perforated plastic distribution pipes laid in gravel trenches over a layer of soil. In most provinces, the soil layer must be a minimum of 0.7 – 1.2 m above the high ground water table or a restrictive layer such as bedrock or clay and have a certain permeability (absorptive capacity). Older systems may have been constructed with clay tiles instead of plastic pipes, while new systems may use plastic chambers to replace the gravel trenches and perforated piping. The actual size, design and layout of the leaching bed is defined in provincial/territorial code or regulation and is based upon the volume of sewage generated, the absorptive capacity of the underlying soils, and the depth to the high groundwater table or limiting/restrictive layer. Wastewater can flow by gravity from the septic tank to the distribution lines, or where required, can be collected in a pump chamber and pumped to a leaching bed at a higher elevation.

The leaching bed is a soil filter which uses natural processes to treat the wastewater from the septic tank. Contaminants in the wastewater include solid and dissolved organic matter (carbon compounds), nutrients (nitrogen and phosphorus) and harmful bacteria and viruses. A slime layer of bacteria, called a “biomat” layer, forms at the bottom and sidewalls of each distribution trench; and it is in this layer where much of the treatment occurs. Bacteria in the biomat layer and surrounding soils consume the organic matter in the wastewater as well as transform ammonia nitrogen, which is toxic to some aquatic species, to the less toxic form of nitrate-nitrogen. Harmful bacteria and viruses present in the wastewater are largely removed in the leaching bed through filtration, predation (eaten by other microbes) and environmental exposure. Some leaching bed soils will contain iron, aluminium or calcium which can adsorb phosphorus from the wastewater. The soil bacteria which perform the treatment require oxygen to function; therefore the leaching bed must be installed in soils that are not saturated by surface water run-off or a high groundwater table, and should not be paved or covered over with pavement, patios, sheds, and so on.

The leaching bed soil must be the right type to retain the wastewater long enough for treatment to occur, while at the same time allowing the wastewater to infiltrate into the ground (refer to your provincial or territorial regulations).

In cases where there is a sufficient separation from either the high groundwater table or bedrock, the network of drainage piping is installed directly in the native soil or in imported sand if the permeability of the native soil is not suitable. This is called a conventional system (see Figure 3). In cases where the high groundwater table or bedrock is close to the surface, the leaching bed must be raised so that there is sufficient unsaturated soil under the drainage piping. This is called a raised (bed) system or a mound system (see Figure 4).

 What Do I Need to Do to Keep My Septic System Working?

Access Risers

Having easy access to the septic tank is the first step to routine maintenance. For tanks that are buried in the ground it is a very good idea to install access risers, which extend the tank lids to or near the surface (see Figure 2). Should there be a need to access the tank during the winter, risers will make the job much easier. Risers can be made of plastic or concrete and must be secured against entry.

Tank Pump-out

Over time, the sludge will build up in the bottom of the septic tank. If the sludge is allowed to accumulate it will eventually flow into the leaching bed and rapidly clog the distribution pipes. Once the pipes become clogged, the wastewater will either seep to the surface of the ground, or worse yet, back up into your house. Not only can a clogged septic system be hazardous to the environment and to your family’s health, it also represents a very expensive repair bill.

A septic tank should generally be pumped out every three to five years or when 1/3 of the tank volume is filled with solids (measured by a qualified practitioner). The frequency of pumping out the tank will depend upon household water use (number of people) and the size of the septic tank. For example, a family of five with a 2,300 L tank may require a tank pump-out as frequently as every two to three years, while a retired couple with a 3,600 L tank may only require a tank pump-out every five to seven years. Some jurisdictions define how frequently a septic tank must be pumped out. In the province of Quebec, for instance, septic tanks are required to be pumped every two years for full time residences and every four years for seasonal residences.

The best time to have the tank pumped out is summer to early fall. At these times, the ground will not be frozen, allowing easier access to the tank, and the biological activity in the tank can re-establish itself before it gets too cold (micro-organisms like it warm). In the spring, a high water table caused by melted snow can sometimes create sufficient pressure on the underside of an empty tank to push it up out of the ground. This is more of a concern with lighter tanks made of polyethylene or fibreglass than those made of concrete.

Never inspect or pump out a septic tank yourself. There is no oxygen in the tank for you to breathe and the tank contains deadly gases which can kill you in only a few seconds. When it is time to clean or inspect your tank, call a licensed pumper.

Effluent Filters

An effluent filter is a relatively new accessory for a septic tank. It is a simple filter which is installed at the outlet of the septic tank to prevent large solid particles from flowing out of the septic tank and into the leaching bed. An effluent filter could prevent the premature clogging of your leaching bed with solids. There are many different effluent filters on the market, so consult with a local contractor to determine which filter is best for your system. Effluent filters need to be cleaned periodically depending upon the type and size of filter and household water use. Some filter models can be fitted with an alarm which sounds when the filter requires cleaning.

What Not to Put Down the Drain

Because septic systems rely on bacteria to break down the waste material, it is important that you don’t poison these micro-organisms. Even small amounts of paints, solvents, thinners, nail polish remover and other common household compounds flushed or poured down the drain can kill the bacteria that break down the organic matter in the wastewater. Household disinfectants such as laundry bleach or toilet bowl cleaner can be used in moderation without affecting the operation of the septic system; however, overuse of disinfectants can kill the bacteria in a septic tank. Some manufacturers promote the use of septic tank “cleaners”, “starters” or “enhancers” to aid in the digestion of the waste. These products are typically of little value and are not recommended.

You should avoid putting anything into the septic system that doesn’t break down naturally or anything that takes a long time to break down. Materials such as oils, grease, and fat, disposable diapers, tampons and their holders, condoms, paper towels, facial tissues, cat box litter, plastics, cigarette filters, coffee grounds, egg shells, and other kitchen wastes, should never be put into the septic system. You should also avoid the use of in-sink garbage disposal units (“garburators”) unless the septic tank and leaching bed are designed to accommodate the increase water and organic load created from these devices.

How Do I Look After the Leaching Bed?

Looking after the leaching bed is easy. There’s nothing you have to do, but there are a few things you shouldn’t do. The area over the leaching bed should have a good cover of grass. Good ventilation and adequate sunlight should also be maintained to promote evaporation. This means that nothing should be constructed over the leaching bed including: parking areas, patios, tennis courts, decks or storage sheds. Covering the leaching bed will prevent oxygen from getting into the soil. The bacteria responsible for digesting the wastewater need oxygen to survive and function.

You should not drive vehicles or machinery over the bed, as the weight could crush the distribution pipes or compact the soil. In winter, you should also keep snowmobiles off the leaching bed. The compaction of the snow will reduce its natural insulating effect, increasing the chances of the pipes freezing.

Don’t plant trees or shrubs near the leaching bed. The roots of some trees, especially willows and poplars, will travel significant distances to reach water. The roots can plug and damage the distribution pipes. Lastly, don’t water the grass over the leaching bed and ensure that all surface drainage (particularly eave troughs) is directed away from the leaching bed. The additional water may interfere with the ability of the soil to absorb and treat the wastewater.

The leaching bed of a conventional septic system should last at least 20 years; however, the distribution lines will eventually become clogged with biomat and the bed will have to be repaired or replaced.

How Will I Know if I Have a Problem with My Septic System?

Some of the warning signs that your septic system may be failing include the following:

  • The ground around the septic tank or over the leaching bed may be soggy or spongy to walk on.
  • Toilets, showers and sinks may back up or may take longer than usual to drain.
  • Occasional sewage odours may become noticeable, particularly after a rainfall.
  • Gray or black liquids may be surfacing in your yard or backing up through fixtures into the house.
  • E. coli or fecal coliform indicator bacteria may be found in nearby well water or in a surface ditch close to the leaching bed.
  • The water level in the septic tank is higher than the outlet pipe (this indicates that the water is ponding in the distribution lines) — inspection should be conducted by a qualified practitioner.
  • Wastewater is ponding in the distribution lines — inspection should be conducted by a qualified practitioner or an engineer.

Your Septic System and the Law

You are required by law to report any problem to your local authorities before proceeding with repairs or replacement. A final inspection will need to be carried out and a Use Permit granted before you can legally use a new or altered septic system. Your contractor and/or your local authorities can also help you determine the required size of your septic system. You may find that you need a larger system than you currently have. If you are repairing, replacing or installing a new septic system, you will also have to be aware of the legal limitations imposed on where your septic system can be located with respect to your house and your well, your neighbour’s house and well, and nearby bodies of water. These distances are required to help ensure that wastewater from your septic system cannot reach and contaminate nearby water supplies. Depending upon the province, the leaching bed must be at least 1.5 – 9 m from a property line, 3 – 1 m from a building, 15 – 30.5 m from a well, and 15 – 75 m from a body of water.

The agency responsible for onsite septic system permits in Ontario is the Ministry of Municipal Affairs and Housing under the Ontario Building Code Part 8.

Where Can I Get More Information?

  • ministries responsible for septic systems (e.g. environment, health)Local municipal offices or public health offices
  • Licensed septic system installers (check the Yellow Pages™)
  • Provincial and territorial
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