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Wollongong City Council

Changing an Onsite Sewage System

You can stop using an old onsite sewage system if you connect to the Sydney Water sewer network, or if you install a new, approved system.

If you no longer need your old system, you can either decommission it or, in some cases, reuse it to store water for watering gardens and lawns.

Under no circumstances can onsite sewage systems be reused to hold water for domestic washing or drinking purposes.

Council approval is not needed to decommission and/or reuse an onsite sewage system, but you must take care when doing this to protect public health and the environment.

You need to tell Council if you stop using an onsite sewage system - email or call us on (02) 4227 7111.

The information below is provided as a general guide only, based on recommendations from NSW Health.

Talk to a qualified professional if you need help.

If you will not be reusing a septic tank or well, follow the steps below to decommission it:

  1. Get the contents removed by a pumpout tanker
  2. As the contents are being removed, hose down the sides, lid, baffle (if fitted) and square junctions of the tank
  3. Disinfect the tank by spreading hydrated lime over all exposed surfaces. Do not climb into the tank to do this.
  4. Punch several holes into the bottom of the tank.
  5. Any parts of the system that are above ground should be demolished and collapsed into the tank
  6. Fill the tank with clean soil.

If you will not be reusing an aerated water treatement system (AWTS), follow the steps below to decommission it:

  1. Get the contents of the AWTS removed by a pumpout tanker. This needs to include any liquid, which is not to be irrigated to the land application area.
  2. As the contents are being removed, hose down the sides, lid, baffle, square junctions and any other parts of the AWTS.
  3. Internal parts such as pumps and blowers should be collapsed into the AWTS, or selectively removed for use as spare parts. If parts are being removed, care must be taken not to contaminate the environment or create a health or safety risk to the person removing them, or anyone else.
  4. Disinfect the AWTS by spreading hydrated lime over all exposed surfaces. Do not climb into the tank to do this.
  5. Punch several holes into the bottom of the tank.
  6. Any parts of the system that are above ground should be demolished and collapsed into the tank.
  7. Fill the tank with clean soil.
  8. Flush all irrigation lines, spray heads, sprinklers and drippers with clean (potable) water for 5 minutes. If irrigation lines are to be connected to the main water supply, you will need to follow any relevant Sydney Water requirements.

You may be able to reuse an old tank, well or aerated water treatment system (AWTS) to store roofwater for watering the garden or firefighting. You should only do this if the tank or system is still in good condition.

If the system is damaged or not structurally sound you should decommission it. See the sections above for details.

These steps should be followed to reuse an old system:

  1. Get the contents of the system removed by a pumpout tanker.
  2. As the contents are being removed, hose down the sides, lid, baffle and square junctions.
  3. Mosquito-proof the tank.
  4. Fill the tank with clean water and disinfect it to a minimum of 5mg/L of free residual cholorine with a half hour contact time. The chlorine should be allowed to dissipate naturally, and not be neutralised. After chlorinating, do no use the water for at least seven days as this could damage plants.
  5. Seal the inlet and outlet, then install and connect any pumps or irrigation lines. Keep in mind:
    1. Water and irrigation fittings must be non-standard so they cannot be connected to any potable (drinking) water supply.
    2. Check with the pump supplier that it is suitable for the site, especially if it will be used to pump stormwater overflow into street gutters.
    3. Use a licenced electrician for any electrical work related to pump installation. Make sure a safety cut-off switch is installed.
  6. Only roofwater pipes can be connected to the tank/s.
  7. An overflow pipe should be fitted to the tank. This should be connected to a drainage easement system, street gutter or existing absorption trench.
  8. Label the tank and any taps supplied by the tank with warning signs to let people know the water is not fit for human consumption. Warning signs should have:
    1. a yellow background
    2. all capital letters at least 20mm high
    3. the appropriate symbol for non-potable water
    4. text along the lines of ‘WARNING: WATER FOR IRRIGATION PURPOSES ONLY – NOT FOR DRINKING'.
  9. For the first two months after converting the system, regularly test the chlorine levels of the water. Keep chlorine levels between 1.5 and 5 mg/L.

You must make sure that the system does not cause any drainage nuisance to nearby properties.

If septic tanks are left empty, they can lift out of the ground because of ground water pressure. Talk to a plumber or the tank manufacturer if you need advice about the requirements for your specific system.