How Your Septic System Actually Works
The rest of this FAQ answers the everyday questions homeowners ask most often. Where a New Brunswick rule applies, it is noted.
25 questions in this section
- What happens to wastewater after it leaves my house?
- What are the three layers in a septic tank?
- What does the bacteria in my tank actually do?
- Does the septic tank treat the wastewater completely?
- What is the disposal field, drain field or leach field?
- What is a biomat?
- Why do disposal fields have several trenches instead of one big one?
- What is a header?
- What is an inspection port or riser?
- What is effluent?
- What is septage?
- What is a gravity system versus a pumped system?
- What is a pressure-dosed system?
- Why is a mound system more expensive than a trench system?
- Do septic systems smell?
- Where do the gases from my system go?
- Does my system need electricity?
- What happens to my system during a power outage?
- Is a septic system bad for the environment?
- How much water does an average household send to a septic system?
- Can two houses share one septic system?
- What is a communal or cluster system?
- What is an aerobic treatment unit?
- Does a bigger tank mean I never have to pump?
- How is a septic system different from a cesspool?
What happens to wastewater after it leaves my house?
It flows by gravity down a sloped pipe into the septic tank, where it sits long enough for solids to settle and grease to float. The relatively clear liquid in the middle flows out to the disposal field, where soil and bacteria finish the treatment before the water rejoins the groundwater.
What are the three layers in a septic tank?
Sludge on the bottom, made of settled solids. Scum on top, made of fats, oils and grease. Effluent in the middle, the clarified liquid that flows out to the field. Only the middle layer should ever leave the tank.
What does the bacteria in my tank actually do?
Anaerobic bacteria break down organic solids, reducing the volume of sludge and partially treating the wastewater. They do not eliminate sludge entirely, which is why pumping is still necessary.
Does the septic tank treat the wastewater completely?
No. The tank is a settling chamber that does primary treatment. The real purification happens in the soil beneath the disposal field, where aerobic bacteria, filtration and time remove pathogens and nutrients.
What is the disposal field, drain field or leach field?
Three names for the same thing: the network of perforated pipe or chambers in gravel that distributes effluent into the soil. New Brunswick's Guidelines use the term disposal field.
What is a biomat?
A thin biological layer that forms at the soil interface in the disposal field. A healthy biomat slows the flow of effluent and helps treat it. An overloaded system builds an excessive biomat that clogs the soil and causes failure.
Why do disposal fields have several trenches instead of one big one?
To spread the effluent over a wide area of undisturbed soil and to keep any single trench from being overloaded. Equal distribution across all lines is a core design requirement.
What is a header?
The non-perforated, level pipe at the top of the field that feeds the individual distribution lines. Keeping it level is what makes distribution equal.
What is an inspection port or riser?
A vertical pipe brought to or above grade so the tank, distribution box or field can be checked and serviced without digging. Risers are one of the best small investments a septic owner can make.
What is effluent?
The liquid that leaves the septic tank. It is clarified but not clean, and still contains bacteria, viruses and nutrients that the soil must treat.
What is septage?
The combined sludge, scum and liquid removed from a septic tank when it is pumped. It must be hauled by a licensed septage hauler to an approved receiving facility.
What is a gravity system versus a pumped system?
In a gravity system, effluent flows downhill from the tank to the field on its own. In a pumped system, a pump lifts or pressurizes the effluent. Pumped systems have more parts to maintain and more to go wrong.
What is a pressure-dosed system?
One where effluent is delivered to the field in measured doses under pressure, rather than trickling out continuously. Dosing spreads effluent more evenly across a large field and gives the soil time to recover between doses.
Why is a mound system more expensive than a trench system?
Because a mound requires imported sand that meets a strict gradation specification, careful scarification of the native soil, an apron and taper, and much more earth-moving. Materials and machine time are the difference.
Do septic systems smell?
A properly working system should not produce persistent outdoor odours. Occasional whiffs near a vent on a still, damp day are normal. A constant smell in the yard or house is a warning sign.
Where do the gases from my system go?
Up the plumbing vent stack on your roof. That vent is part of the septic system, not just the plumbing, and a blocked vent can cause gurgling drains and odour.
Does my system need electricity?
A conventional gravity system does not. Systems with a pump, an aerator, an alarm or any treatment unit do, and will stop working correctly during an extended power outage.
What happens to my system during a power outage?
A gravity system keeps working. A pumped system stops moving effluent to the field, and wastewater backs up in the pump chamber. Reduce water use immediately and avoid laundry and long showers until power returns.
Is a septic system bad for the environment?
A properly sited, sized and maintained system is a legitimate wastewater treatment method that returns treated water to the local groundwater. A failing or undersized system is a genuine source of pathogen and nutrient pollution.
How much water does an average household send to a septic system?
Roughly 40 percent from toilets, 30 percent from the bathroom, 15 percent from laundry, 10 percent from the kitchen and 5 percent from other sources, according to New Brunswick septic service providers.
Can two houses share one septic system?
This requires specific approval and design, and the system must be sized for the combined flow. In practice it introduces legal and maintenance complications. Discuss it with a licensed installer and Technical Inspection Services before assuming it is possible.
What is a communal or cluster system?
A shared system serving several properties, typically owned and operated by a municipality or a legal entity. In New Brunswick, a holding tank may be approved as an interim measure where a communal sewerage system is confirmed to be coming within one year.
What is an aerobic treatment unit?
A system that injects air to support aerobic bacteria, producing much cleaner effluent than a septic tank alone. In New Brunswick these are non-conventional systems requiring engineering or a special installer licence, and they need regular servicing and electricity.
Does a bigger tank mean I never have to pump?
No. A bigger tank buys more time between pumpings but sludge still accumulates. Every tank needs periodic pumping regardless of size.
How is a septic system different from a cesspool?
A cesspool is simply a pit that lets raw sewage seep into the ground with no treatment. It is obsolete and not permitted. A septic system separates solids and delivers clarified effluent to soil designed to treat it.
Have a question about your own property? General answers only go so far — your soil, slope, water table and setbacks are specific to your lot. Call (506) 233-6272 or send us the details.
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