Frequently Asked Questions

A septic system has two key components; a septic tank and a septic dispersal field.

The septic tank allows for the solids to settle, where naturally occuring bacteria break down the sewage and partially treat it. The cleaner sewage, called effluent, is either further treated, depending on the system, or is dispersed into the soil.

The septic dispersal field allows for the overflow effluent from the septic tank to drain into the soil, where naturally occuring bacteria further treat the effluent. When designed correctly, by the time the effluent reaches the water table in the soil, the effluent is completely clean.

There are three types of septic systems; type I, type II, and type III. 

Type I septic systems include a septic tank and a septic field. This provides basic treatment to the sewage, the solids settle and naturally occuring bacteria break down the sewage, before being dispersed into the soil.

Type II septic systems are similar to type I systems with the addition of a treatment tank. The treatment tank is filled with a mesh film to increase the area available for bacteria to grow on and an air blower is installed so that bacteria requiring oxygen can grow. Bacteria that require oxygen break down sewage more effectively than bacteria that don’t require oxygen in type I systems. 

Type III septic systems are similar to type II systems with the addition of a UV light. The UV light further breaks down the effluent from the treatment tank by killing any pathogens in the effluent. There are other options for type III systems than UV lights, but these are less common.

Most new systems with a power supply will also have an additional pump chamber/tank, where a pump is installed to pump the effluent to the septic field. 

Other type II systems exist that don’t need air blowers or oxygen-bacteria to clean the effluent to type II levels, but these are less common and are usually only used on sites without a power supply. They utilize organic materials like coconut, woodchips, and peat moss to treat the effluent.

Several factors are considered when choosing the type of septic system for a site, but basically a higher type septic system will result in a smaller septic field size as the effluent is cleaner. 

Thus, a higher type septic system may be installed if:

• the site is small
• the soil is poor
• groundwater or the water table is high
• the system is near a water course
• the system is near farm crops

Soils that are poor for septic fields are soils that won’t allow water to drain through it well. These include sites that have:

• soil that is compacted/packed tightly
• soil with lots of clay
• soil within the water table

Clay acts as an impermeable floor for water to flow through as the particles are very small. Much like the clay pots you may have in your home, minimal water is absorbed by the material. A good indication of high clay content in a soil is to see if the soil has a similar consistency to play-doh when wet.

The water table elevation fluctuates throughout the year and typically peaks in the spring from snow melt and rainfall.

The elevation of the seasonally high water table can be found by digging a test pit and looking for mottling and gleying. Mottling is the formation of rust spots in the soil from iron rusting when in contact with the water table and gleying is the formation of a grey colored soil caused by the water table dissolving the minerals in the soil.

Sand mounds are septic fields that are installed above the existing ground level using septic sand. These systems are installed when there is a minimal depth of good soil to treat the septic effluent and use septic sand as fill to create a depth of soil and sand that will treat and clean the effluent. Septic sand is a specific grade of sand that acts as a filter to treat the septic effluent and is different than river sand.

The depth required to install a septic field can vary anywhere from 1.5 ft to 3.5 ft on a level site, and up to 6 ft on a highly sloped site. In some cases, removing this depth of soil so that the septic field is completely underground is not possible as stripping the required depth would significantly or completely remove the layer of usable soil to treat the effluent. Typically, as you go deeper into the ground, the soil conditions worsen for septic fields. In these situations, we are forced to install a system partially or completely above grade.

On sites that have larger depths of usable soil, stripping away the required depth will still leave enough soil below it to treat the effluent and in these cases an underground septic field can be installed.