What is a Septic Sewer System?

In rural or semi rural areas where municipal water and sewage lines are unavailable, home owners must provide their own water and sewage systems.

A safe and effective septic system consists of an underground tank and a leach or drain field that work to cleanse and purify household waste water.

Permits are required from the local Health Authority before installation of a septic system.

Sewage Emission

The average individual uses anywhere from 50 to 350 gallons (227.3 to 1,591 litres) of water per day for drinking, cooking, washing, flushing the toilet, and other household purposes. 99.9 percent of sewage is water. The remaining 0.1 percent is solid. This solid component is 80 percent organic and 20 percent inorganic. The organic substances derive from feces, detergents, soaps, urine, and food bits produced by garbage grinders. Water softeners, borax, paint, photographic chemicals, household cleaners and the like are the sources of the inorganic solids found in household sewer lines.

About 50% of sewage is Gray Water. It is less polluted water, such as the water from the kitchen sink, the shower and the bathtub. The other 50% is Black Water. This is the water used to flush the toilet.

The Sewer Line

Sewage flows by gravity (1/8″ per foot fall) from the house’s main drain outlet through the sewer line to the septic tank. In single family residences, a 4″ plastic PVC or ABS solid-walled and tight-coupled pipe is used. Occasionally sewage must be mechanically pumped upward into a tank at a higher level. Where the building sewer is steeply graded, the last pipe section may need to be levelled, or nearly so, to reduce velocity. Excessive grade/fall and speed must be avoided so that the stilling action in the tank is not compromised. Pipe should be buried as a precaution from frost, foot traffic, and animals.

The Tank and Its Function

The tank is a large watertight, light proof and relatively air tight container positioned beneath grade level. The septic tank has a sewer line inlet and a lower outlet on the opposite side or end that leads to the leach field.

The purpose of the septic tank is to still the flow of sewage from the building and contain it long enough for anaerobic bacteria to digest the fecal and other organic matter. This period is estimated to be from three to five days. The tank must therefore be large enough to contain at least three days’ worth of sewage. Because you don’t want to replace a tank every few years, it must be made of some rot and rust-resisting material.

Tanks are commonly made from several materials, and are chosen because of their affordability and life span. Types of materials include: polyethelene, metal, cast concrete, concrete block, and brick. Of these, cast concrete and polyethelene can last indefinitely, and are commonly used in the Niagara Region.

Sizing a Tank

Statistically, probably because of the abundance of water in Canada, Canadians use more and dirty more water than any other nation in the world.

According to the Environmental Protection Act (EPA), for purposes of computation, a daily sewage flow of 275 litres (61.6 gallons) per person is recommended for tank design to account for the individual share of all types of water use in a house having modern appliances.

No. of Bedrooms                                  Daily Sewage Flow (Litres)

2 or less (4 People)                                     1100 (242 gallons)

3 (6 People)                                                1600 (352.4 gallons)

4 (8 People)                                                2000 (440 gallons)

Over 4                                                         add 300 litres (66 gallons) per bedroom

Septic tanks for residences of up to 5 bedrooms shall have a minimum working capacity in accordance with this table:

No. of Bedrooms                             Minimum total working capacity

(allows 2 persons per bedroom) (litres) (gallons)
2 2700 594
3 3600 792
4/5 4500 990

Note: Where the number of occupants is known and exceeds two times the number of bedrooms, the tank size  selected should be that which relates to the next higher number of bedrooms.

If daily sewage flows are 3600 litres (792 gallons) or less, tank capacity shall not be less than twice the daily sewage flow. If daily sewage flow is in excess of 3600 litres (792 gallons), the tank must be no less than 3/4 of the daily sewage flow plus 4500 litres (990 gallons).

In larger tanks a maximum depth of 1800 to 2000 millimetres (70 to 78″) is recommended. A ratio of length to width such that the length is 2 to 3 times the width is recommended for good proportions.

Computation of the daily sewage flow to be used in design of the sewage system is most important. An applicant for approval of a sewage system should discuss with the approving authority prior to commencing design. Agreement should be reached on the total daily sewage flow, on the average of daily sewage flow where it varies from day to day, and on the flow pattern within peak days.

Certified tanks only are to be used. Manufacturers have strict regulations to follow, and are certified by the CSA or the Underwriter’s Laboratories of Canada.

Location of Tank

  1. Must be accessible for pumpout/cleaning
  2. Minimum 1.5m from house
  3. Minimum 3m from property line
  4. Minimum 15m from lake, pond, reservoir, river, stream, spring or well

The Leach Field

The effluent from the septic tank is carried into the leach field through perforated plastic pipe or short lengths of loosely joined clay pipe. The liquid flows out of the pipe and through the coarse gravel in which the pipe is bedded. As the effluent flows through the earth, it is filtered.


  • The field should be as far away as possible from all water wells (your own and your neighbours’): 100 linear feet is a typical minimum
  • The field should be on ground lower than the ground on which any water wells are
  • The spot selected should not be a natural sump where rain collects and
  • The field should be positioned on the sunny side of the building or
  • The field should not be close to trees or shrubs, as roots can easily clog and destroy drain field pipes (root systems are about equal in size and extent to branch systems). Trees and dense shrubs also cast heavy shadows that slow evaporation and tend to keep the soil damp and cool enough to freeze sooner in cold weather.
  • The earth in which the drain pipes will be buried should be highly permeable.

Natural Effluent Treatment Process

The effluent that flows from the tank outlet is still septic: it contains substances that promote the decomposition of vegetable and animal matter as well as pathogens, bacteria, and viruses harmful to man and beast. The effluent cannot just be dumped. It must be treated. This is where nature steps in. During the time that household sewage remains in the septic tank, heavy particles sink to the bottom where anaerobic bacteria attack and digest the organic material. The resulting effluent, as it is displaced by fresh incoming sewage, flows into the leach field, where aerobic bacteria convert the remaining organic material to soluble, stable plant nutrients.

As the effluent flows through the earth it is filtered. Large particles are stopped by grains of clay and sand. Viruses are attracted to the surfaces of stone particles, stick, and die. Much of the now purified water finds its way downward to a water table; some returns to the surface and is dissipated through transpiration and evaporation. The downward movement must be slow enough to provide sufficient time for this action to result in an acceptable level of treatment of the sewage before it enters the water table, or reaches rock or a soil of unacceptable permeability. The soil in the treatment zone is specified by regulation as to the minimum depth and to both minimum and maximum percolation times, in order to ensure continued satisfactory operation. Percolation is the rate of water dispersion into the type of available soil. Adding soils may be necessary to ensure a good mix.

Sizing a Leach Field

The size and layout of a leaching bed will be determined from:

  1. the daily sewage flow
  2. the soil
  3. other site characteristics in the area proposed for construction of the

A loading rate is established which, considering the characteristics of the sewage and the filter medium, can be sustained without clogging the filter medium. The absorption trenches should be not more than 30m (98.4 ft.) in length. The maximum of size of field is 50 square metres (538.19 square feet).

Earth Choice

The ideal drain field soil is light, airy, porous, and dry. Unfortunately, few septic system site soils have these properties and you must ascertain what sort of soil you actually do have. If there is any choice for field location, you must also determine which area contains the best soil for leaching purposes. Important physical properties of soil are texture, structure, consistency and sensitivity, plasticity, clay mineralogy, shrinkage and liquidity indexes, colour and density.

The two factors commonly used to rate soil for purposes of its use in a sewage disposal system are:

The Coefficient of Permeability: Measured in centimetres per second or metres per day, it is a measure of the ease with which liquid will pass through the soil. The Coefficient of Permeology is determined by laboratory tests conducted on site samples.

Percolation Time: Measured in minutes per centimetre and defined as the average time in minutes that is required for water to drop one centimetre during a soil percolation test.

Soil Samples

A positive way to determine soil composition is to contact Canadian Home Inspection Services to drill the soil at numerous test sites in the potential leaching areas, make its assessments, and furnish you with a report. Let it be noted that tests are carried out at owner’s expense.


The purpose of the percolation test is to determine by actual experiment the rate at which the soil in your proposed drain field can absorb water. This is done by repeatedly pouring water into one or more holes in the ground and timing the rate at which the water disappears. There are various procedures and variations thereon for making this test, which often depend upon the requirements of the local testing or inspecting authority.

Problem Detection

The life span of the leach field depends upon its use, size, and the kind of soil that surrounds it. When the soil immediately around the pipes becomes saturated and clogged with fine particles of solid matter, the soil loses its ability to function as a filter. The effluent cannot flow easily from the lines and disperse. As a result, the effluent will back up and appear on the ground surface, causing a distinctive and unpleasant odour. Thus, the system has a built-in alarm that warns the homeowner or buyer of trouble.

Restoring a Leach Field

When a drain field has reached the end of its useful life, it can be brought back and made an effective filter again by removing the old gravel and the clogged earth immediately adjacent, treating the nearby remaining soil, and replacing the gravel field and covering it with a layer of fresh soil.

Sewage System Design Overview

A Sewage System will vary as to size, component parts and layout depending upon such variables as:

  • The daily sewage flow and the pattern of this sewage flow within any one
  • The site conditions including topography, surface and subsurface drainage, soil stratification and characteristics, particularly soil permeability, existing and design water table and the prevalence of
  • The relative elevation of the components of the sewage system in relation to the building(s) served and to each
  • Changes of usage. This may go up or down when people move in or out, and remedial measures are not limited to replacing a tank or leach For instance there are measures to cut back the amount of sewage created, and system designs that separate the waste products before treatment takes place. These solutions should be discussed with Canadian Home Inspection Services and/or your local Health Authority.

Real Estate Agents Checklist for Septic Systems

  1. Check history/records of the septic sewer system, including date of latest tank. As ownership changes, it must be underlined that the lifestyles and number of the prospective new occupants may overload the septic sewer system. Therefore it is vital to know:
    1. If there is proper flow into the (A dye test may be required).
    2. Tank capacity, and
    3. If tank requires
    4. If there is adequate water dispersion in the leach
  2. Ask owners about any problems and dates of
  3. Visual evidence
    1. Is septic system on fall graded land?
    2. Is there enough distance from septic system to water well?
    3. Check leach bed for location, ponding or odour and trees that are too close.

In Summary

Canadian Home Inspection Services Inc. has noticed increased concern for full disclosure of septic sewer systems before Real Estate transactions take place.

Through rising concerns over poorly constructed septic systems, the Environmental Protection Act has incorporated stricter regulations for the installation of new systems. Much of the concern however, is over older systems. To address this issue, there have been proposals to require mandatory septic system inspections upon the sale of the dwelling.

Lawsuits involving Purchasers, Sellers, Real Estate Agents, and Lawyers have prompted the concern for full disclosure. It is important to remember that while a well-maintained and non-abused septic system can last almost indefinitely, a septic sewer system assessment should form an integral part of a real estate transaction.

Canadian Home Inspection Services Inc. will, therefore, perform a thorough investigation of a septic system by examining the effectiveness of the disposal process beginning from initial waste depot such as toilets and sinks, to the dispersal of sewage through leaching beds.