What Are the Different Types of Septic Systems?


Table of Contents

With many different types of septic systems choosing a septic system for your home can be quite a daunting task, considering that there are several different types of septic systems available, and often a number of options to choose from within each type.

Determining the right septic system type is based on these factors:

1) It is important to select the most appropriate septic system for your soil conditions

2) The system must adequately meet your household needs

3) The wastewater must be treated sufficiently to ensure the effluent that is discharged complies with local environmental health standards

Different Types of Septic Systems 

There are three types of septic systems, categorized according to the manner in which they treat wastewater that enters the system as follows:

Type 1 Septic System

In a type 1 septic system, sewage is treated within a septic tank only before being discharged to a drain field, where further treatment occurs naturally.

Type 2 Septic System

In a type 1 septic system, treatment takes place within a septic tank plus an additional aerobic treatment unit, typically within a small-scale on-site mechanical biological packaged treatment plant, before being discharged to a drain field.

Type 3 Septic System

A type 3 septic system is a specially designed septic system that is capable of treating sewage to produce effluent of a higher quality standard, by including a disinfection process before being discharged into the environment via the drain field. Treatment takes place within an advanced on-site mechanical biological packaged treatment plant.

It is important to choose the most appropriate septic system for your property, as the wrong choice of system can end up being an expensive mistake.

Let’s take a closer look at the differences between each type of septic system to help you decide which is the best option for your situation.

Type 1 Septic System (Septic Tank System)

A Type 1 septic system is defined as an on-site septic system where a septic tank is the primary means of treating sewage.

The treated effluent can then be disposed of in a drainage field that can consist of seepage beds, sub-surface trenches, or above-ground sand mounds. Effluent can either flow to the drain field via gravity or it can be pumped to the drain field under pressure.

different types of septic systems
Conventional septic system

Type 1 septic systems are a suitable choice for properties where the soil conditions are ideal for disposing of the effluent into the ground. They consist of a septic tank installed underground, which receives the wastewater.

Once the wastewater is in the septic tank, the suspended solids settle down to the bottom, forming a layer of sludge, while the less dense oil, grease, and fat float to the surface, forming a layer of scum.

septic tank

Because the septic tank is free of oxygen, it provides conditions that allow anaerobic bacteria to thrive. The community of anaerobic bacteria living in the septic tank breaks down the solids, reducing the volume by about 50-60%.

The watery effluent is sandwiched between the layer of scum on the surface and the layer of sludge on the bottom. This wastewater flows out from the septic tank into a drain field where it is disposed of into the soil.

Naturally occurring microorganisms that live in the soil provide further treatment by removing any harmful bacteria and pathogens before the effluent reaches the groundwater. The solids (scum and sludge) remaining in the septic tank need to be pumped out on a regular basis.

Type 2 Septic System (Septic Tank + Secondary Treatment)

The main difference between a Type 1 and a Type 2 septic system is that a Type 2 septic system includes an additional secondary wastewater treatment stage.

As with a Type 1 system, the anaerobic bacteria break down the solids in the oxygen-free septic tank. During the secondary treatment process, oxygen is typically added to the wastewater which allows aerobic bacteria to flourish in the system.

The aerobic bacteria break down any suspended solids that may be present in the wastewater.

Extending Drain Field Life with Aerobic Septic Systems

Some experiments have suggested that retrofitting an aerobic septic system to an existing conventional septic system may rejuvenate or extend the life expectancy of that system. Adding aeration or oxygen to an existing septic system may boost the aerobic bacterial action in the biomass, which can improve the septic field from a malfunctioned state. Although not quite that simple.

A settling compartment or additional septic tank may be required with an effluent filter because the agitation from the aerating can send suspended solids out into the septic field, which would lead to eventual clogging.

Benefits of a Type 2 Septic System

Type 2 septic systems are more efficient at treating wastewater than Type 1 septic systems.

As a result, the effluent that is discharged is cleaner and safer. This is an important factor to consider when a property has poor-quality soils or there is insufficient depth between the surface and the constricting layer or water table to adequately treat the effluent.

Also, because this secondary treatment stage is more effective at breaking down the wastewater than a Type 1 septic system, the surface area of the drainage pipes in the drain field can be less than that used in a Type 1 septic system, and will, therefore, take up less space.

This makes them ideal for use on properties where space is limited. Treatment prior to discharging into the drain field greatly reduces the likelihood that the drain field will clog up with continual use, allowing its size to be reduced.

Disadvantages of a Type 2 Septic System

However, the one drawback is that treatment costs associated with a Type 2 septic system will be higher than those of a Type 1 septic system.

Type 2 Effluent Hydraulic Loading Rate and Vertical Separation

As per our Standards Practice, here is a subsection of our code: III- Type 2 effluent hydraulic loading rate and vertical separation

i) Vertical separation for Type 2 hydraulic loading rates

The use of a Type 2 treatment method is a viable option on many projects and sites (particularly if the available area is limited), although this will seldom be the only viable option.

The Volume II standards indicate a larger vertical separation for Type 2 effluent hydraulic loading rates (HLR) in some cases, particularly for a gravity distribution system and demand dosing.

A larger soil depth is specified to provide for adequate soil-based treatment (particularly pathogen removal) in these cases because:

• Type 2 effluent may have pathogen levels nearly as high as in Type 1 effluent
• Type 2 effluent hydraulic loading rates are higher than for Type 1, and so:
• risk of bypass or saturated flow from the infiltrative surface is higher
• there is a higher risk of soil saturation if multiple doses are applied in a short time
total number of pathogens applied will be correspondingly higher at the higher HLR
• Type 2 systems typically have less or no biomat, resulting in:
• less effective distribution with gravity dispersal
• less moderation of effluent flow to the soil from the infiltrative surface
• less removal of pathogens by the biomat

Since Type 2 treatment systems are often used as a solution for a small site, the standards of this manual allow for high HLR with Type 2 effluent. It is considered that vertical separation can be adjusted, but the site area is generally fixed.

So, the standards prioritize a higher HLR for Type 2 rather than a smaller VS.  However, if Type 2 effluent is applied using Type 1 hydraulic loading rates (HLR) then the standards allow for the use of Type 1 vertical separation standards and Type 1 dosing and distribution standards.

This is because at the lower HLR the shallower VS will be adequate for treatment. For example, a gravity distribution system to Fine Sand Table II- 14 (page II-26) specifies 120 cm VS for Type 2 effluent HLR, but if the effluent was applied at Type 1 HLR, then 90 cm VS could be used.

ii) Type 2 effluent with uniform distribution

The Volume II standards allow smaller vertical separation when timed or micro-dosing options are used with Type 2 HLR. This is because these options lead to lower hydraulic application rates (HAR), more similar to those for Type 1 HLR. They also lead to a lower risk of soil saturation by spacing doses apart. Timed and micro-dosing, therefore, reduce the risk of bypass flows and poor pathogen removal posed by high Type 2 HLR. See Section III- for discussion of hydraulic application rate (HAR).

Timed dosing standards for Type 2 HLR result in higher HAR than for Type 1 HLR. For this reason, on some soils, the standards specify slightly larger VS for Type 2 HLR with timed dosing.
Since micro-dosing ensures the same HAR regardless of hydraulic loading rate, the VS standards are the same for Type 1 and Type 2 HLR on all soil types if micro-dosing is used.

Standards for sand mound and sand lined trench or bed systems allow very high HLR to the sand media with Type 2 effluent, for that reason micro-dosing is required where this high HLR are used.

different types of septic systems

Type 3 Septic System (Septic Tank + Secondary Treatment + Disinfection/Filtration)

Type 3 septic systems are custom-designed sewage treatment plants that treat wastewater to a very high standard, producing clear, odorless effluent that has a much higher water quality than Type 1 or 2 systems.

A Type 3 septic system is required to include a method of disinfection that is capable of removing pathogenic organisms before the effluent is discharged to the drain field.

Type 3 Septic System Components

A Type 3 septic system typically consists of the following components:

1) a septic tank where wastewater is broken down in an oxygen-free environment by anaerobic bacteria;

2) a secondary treatment stage, where oxygen is usually added to facilitate aerobic treatment as with a Type 2 septic system

3) the addition of a third stage, where disinfection takes place.

The disinfection process can incorporate chemical treatment with chlorine, or disinfection with ozone or ultraviolet light, and can include the addition of a filter for more effective removal of pathogens. Finally, the treated effluent is discharged to a drain field, usually under pressure (i.e. pumped rather than gravity-fed).

Who Should Choose a Type 3 Septic System?

Type 3 septic systems are a good choice for properties where soil conditions are very poor and conditions are not suitable for a Type 1 or Type 2 septic system. This includes sites with the following parameters:

  • Soil depth is less than 0.5 feet (15 cm)
  • Soil percolation rates are very slow or very fast
  • Poor soil structure
  • Limited space to install a more conventional septic system.

In cases where conditions are appropriate for a Type 1 or Type 2 system, but space is extremely limited, a Type 3 system may be a better option as a much smaller drain field is required due to the high quality of the effluent discharged.

Different Types of Septic System Video

Here is an explainer video on different types of septic systems from Washington State.  Although the video is from the US, BC regulations are quite similar to Washington standards.


In Conclusion, some of these systems are certainly more complex than others, to be certain of the type of septic system you may require for your lot, a more thorough analysis should be done.

If you have questions about your septic system in BC, be sure to contact us. We’re happy to help. Reach out by email at groundstoneonsite@gmail.com or by phone at 250-768-0056.

Septic System FAQ

Why Does the Type of Septic System Matter?

septic system for a cabin

One may very well ask ‘Why do we need different types of septic systems when they all perform the same job?’

This is true to a certain degree, however, the efficiency of treatment and the water quality of the effluent discharged at the end of the treatment process is higher in a Type 2 system than in a Type 1 system, and higher still in a Type 3 system.

Ultimately, the choice of septic system will hinge on the soil conditions at the site, the amount of space available for a drain field, and/or the need for a higher quality effluent that is cleaner and safer, and that will not pose a risk to the environment or to human health.

How Can I Determine What Type of Septic System is Right for Me?

It is best to have an authorized, qualified professional conduct a thorough site analysis to assess the conditions on site and to determine the amount of wastewater that the household is likely to generate each day.

This will enable them to design an appropriate septic system that is able to cope with the family’s output, taking full cognizance of any limiting factors on-site to ensure that the system is not overloaded and environmental health is not compromised.

What is the Sewerage System Regulation Process?

‘The Ministry of Health provides policy support for land use management, which includes both onsite sewage disposal and subdivision activities. The fundamental goal is to minimize, mitigate and/or prevent potential risks to human health. This is achieved through legislative requirements, supporting policies and guidelines.’   – Govt of Canada Website

What Sewage System is Right for Season Properties?

Type 2 or Type 3 systems may not be suitable for some seasonal dwellings, such as a vacation cottage, because these treatment systems typically run on electricity and may rely on biological processes that cannot be sustained under seasonal use.

When specifying a treatment system at a seasonal dwelling, provide measures to maintain the operation of the system during periods of intermittent power supply and limited water use.

Seasonal use systems should be installed in compliance with the Sewerage System Standard Practice Manual.

Luis Goncalves, ROWP, IN, PL

I fell into this amazing trade quite by accident, I have always loved being around heavy machinery and moving earth and in contrast love working with designing things.  This trade in the septic field has led me down a wonderful path of exploring all of my skills and passions while working hard at achieving success.

Table of Contents

More Posts