Your Septic System (CMHC)

Feb 3, 2016

Where Does the Water Go?

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 (see Figure 1).

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 liquid 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 L depending on the province or territory. 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 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.

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 only 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 (microorganisms 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 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.

How do I Prevent my System from Freezing?

Septic systems are most likely to freeze in periods of cold temperature when there is little snow cover. The first line of defence against system freezing is adequate insulation. Adding 0.3 m (1 ft) of mulch (leaves, straw, hay) or letting the grass grow long over the system in the fall will provide a good insulating layer. Snow can also be piled over the system in the early winter. Other options include: insulate the pipe from the house to the septic tank, add Styrofoam sheets above the septic tank, and increase the soil cover over the system.

There are three major causes of system freezing

  1. Pipes Not Draining Properly – Any standing water in pipes may freeze. This may result from poor installation without sufficient slope or ground settling or frost heaving over time. The solution to this problem is to excavate and replace the faulty section of piping.
  2. Low Water Usage – Water slowly trickling through piping (for instance from a leaking tap or toilet) can create a film of water which can freeze the line solid. Low water use (or vacancy) for an extended period of time can lead to the septic tank freezing. If you are going away for an extended period of time during the winter, it is a good idea to have the tank pumped out before you leave.
  3. Waterlogged System – If your leaching bed is saturated (either through poor design or clogging of the distribution lines) it could freeze solid. If this happens, the only solution is to use the septic tank as a holding tank until spring, when the leaching bed thaws and can be repaired or replaced. This means the septic tank will have to be pumped out every time it fills up, which could be as frequently as twice a week. If you have to use your septic tank as a holding tank, it would be a good idea to have the pumper install a high level alarm in the tank to indicate when pumping is required.

If your system freezes call a qualified practitioner (pumper, installer). Many contractors have high pressure steamers to defrost frozen piping or can install heat tape or a tank heater. Do not add antifreeze, salt or additives to the tank and do not try and run water continuously to unfreeze the system.

Source: Canada Mortgage and Housing Corporation

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