Understanding conventional septic systems

The purpose of a septic tank is to allow solid materials to settle, allow the good bugs time to breakdown the contents of the wastewater, and acts as a storage chamber. The modern septic tank is divided into two chambers which helps the solids to drop out of the wastewater.

A healthy septic tank should have three layers.

The clear effluent flows out of the tank when new wastewater enters the chamber and is discharged to an absorption field (please refer to the diagram below). 

These septic tanks are not mechanical systems and mostly rely on gravity and good bugs to work, which means the system is generally inexpensive to operate when in good working order. 

It is very important to remember that septic tanks do not kill the bad bugs that can make us ill (such as bacteria, viruses and parasites) and the effluent from these tanks must be treated with caution. Contact with people, food, clothing and pets by effluent from septic tanks MUST be prevented. 

Primary issues people encounter with their conventional septic systems include:

• Too much sludge in the septic tank. This can result in the effluent leaving the septic tank being ladened with solid material and clogging up pipes and absorption trenches. Ensure the septic tank is de-sludged regularly and never allow the sludge to be less than 100mm from the bottom of the outlet pipe.

• Too much water going into the septic tank. This  can result in solids being pushed out of the tank and clogging up the pipes and trenches. This is a common problem resulting from the system being undersized to manage the household wastewater or overused. The answer to this problem is to look at the amount of wastewater being generated in your house and reduce it as much as possible (e.g. install water saving devices). The other option is much more expensive and involves increasing the size of the disposal field.
• Toxic chemicals going into the system. Stop toxic chemicals such as bleach or commercial cleaning products from going into the system. These chemicals can kill off the good bugs and will hinder the breakdown of wastewater in the septic tank.

There are usually warning signs of problems in your septic system. If you notice water draining away too slowly, pipes making noises or gurgling when draining, sewage smells, or water ponding near your trenches then these are the signs that your septic system is failing. You will need to contact a licensed plumbing practitioner for assistance and get some help.

Conventional septic tanks overfull with sludge and scum allow untreated wastewater with solid material to flow out of the tank, clogging pipes and the absorption trenches. This is the most common cause of problems with septic tank systems.

You should de-sludge your septic tank every 3-5 years depending on use. Newly de-sludged tanks should be refilled with clean water and a hand full of lime added to reduce any odours and encourage the growth of good bugs.

The following are some helpful hints to keep your septic tank healthy:

• Have your septic system regularly checked for sludge and scum level build up, and blockages by your licensed plumbing practitioner.
• Keep a record of de-sludging, inspections and other maintenance activities.
• Check the household products that you use are suitable for disposal through septic tank systems. Bleaches, solvents, oils, paints, disinfectants, antibiotics, chemical cleaners, pesticides and herbicides, and caustic soda can kill the good bugs in your septic system. You can protect your system by using traditional non-toxic cleaners, like vinegar and bicarbonate of soda, in the kitchen and bathroom.
• Use biodegradable liquid detergents (e.g. concentrates with low phosphorus and salt).
• Ensure that the septic tank is mosquito proof.
• Do not put rubbish such as sanitary napkins, condoms or disposable nappies down the toilet.
• Spread your laundry cycles throughout the week to reduce the disruption of the settling process inside the septic tank.

Your septic tank system has been designed to manage a particular amount of wastewater so be careful not to overload the system. Do not alter any part of your septic tank system without council approval. 

The use of improperly constructed or damaged pump wells can result in contamination of the surrounding environment and odours being generated. For new systems, check that your plumber is using a manufactured pump well approved by your local Environmental Health Officer (EHO). For existing systems, if the pump well is leaking then call your plumber and have it repaired or replaced as quickly as possible.

• The pump well may be undersized for the system and not coping with the wastewater load. This would mean the pump is working continuously and there is inadequate emergency storage capacity within the tank. Call your plumber and have the pump checked and any works required to be undertaken.
• Solids from the septic tank entering the pump well. If this occurs, then your septic tank needs to be pumped out. Septic tanks should be pumped out every 3-5 years depending on use.
• Systems being installed without an alarm to indicate a fault with the electric pump. For new systems, the EHO will not give final approval (issue a Certificate to Use the system) until the alarm has been fitted. For existing systems, you should contact your licensed plumbing practitioner and arrange for an alarm to be retrofitted.
• Pumps failing or power being disconnected. The electric pump installed in a pump well needs to always have power to work effectively. Any issues with the pump or the power supply need to be remedied as soon as possible.