Running and maintaining a septic tank or small sewage plant

If your property is not connected to a public sewer, your sewage is probably dealt with by a private sewerage system. This might be a small package treatment plant, a septic tank, or a cesspit/cesspool. If any of these systems are not maintained or emptied correctly, they can become a health hazard and pollute the environment. It is your responsibility to ensure it works efficiently.

Records of maintenance must be kept for 5 years. Download a maintenance guide and log book to help you manage your system effectively and meet legal obligations.

Septic tanks

Solid material settles to the bottom of the septic tank to form sludge, whilst a scum is formed at the surface. The sludge and scum should be removed periodically and taken away for disposal by a registered waste carrier.

The liquid effluent requires further treatment through a drainage field before discharging to ground, or via other treatment systems such as a reed bed, gravel filter or package treatment plant where a drainage field is unsuitable. Package treatment plants treat the effluent to a higher standard and may allow direct discharge to a suitable watercourse.

Micro-organisms in a drainage field help break down the effluent and the treated liquid eventually pass through to the groundwater. Even when properly maintained, your drainage field may become blocked after several years usage and require replacement.

Maintaining a septic tank

Solids build up over time. If material builds up too much it can flow into the drainage field and lead to clogging. A little effort on a regular basis will save money and significantly prolong the life of the system. You should:

  • ensure the tank is emptied every 12 – 24 months by a registered contractor
  • check the drainage field monthly to ensure it is not waterlogged

Other measures which can help your septic tank run smoothly include:

  • using cleaning products little and often
  • always using the same, phosphate-free cleaning products
  • fitting water saving devices to your toilet cistern
  • adding aerators to shower hoses and taps
  • always doing full loads in washing machines and dish-washers
  • never flushing anything other than human waste and toilet paper
  • not planting trees near your treatment system
  • not disposing of oils, chemicals, fats or solvents in the drain
  • not connecting roof or surface water run-off
  • not parking over or compacting a drainage field

Package Sewage Treatment Plants (PSTP)

Package treatment plants provide a much greater level of biological treatment than a septic tank and may allow direct discharge to a watercourse. A drainage field is still required if discharging to the ground.

PSTPs usually have a mechanical component, providing oxygen to assist with the break-down of organic matter. Most PSTPs require a continual power supply.

In some environmentally sensitive areas, the effluent from a PSTP may require further treatment. Depending on the sensitivity of the environment further treatment may be achieved by a filtration system such as an above ground drainage mound, a reed-bed, a wetland system, or UV disinfection.

Maintaining and servicing your PSTP

Sludge and solids will build up over time in the PSTP and affect the performance. The treatment systems require regular desludging.

Most PSTP require professional servicing every 12 months and detailed checks every 6 months. Maintenance should be carried out by suitably trained and qualified personnel in line with the manufacturer’s specification. This is often through a maintenance agreement with an authorised servicing company.

A list of British Water accredited service engineers can be found on the British Water website.

Registering a septic tank

Any activity involving releasing fluid to the ground or a water course requires an environmental permit. In most instances septic tanks and small treatment plants are exempt from the need to obtain a permit. You must however register your septic tank or small treatment plant as being exempt with Natural Resources Wales.

Under certain circumstances, you may be refused an exemption. You can read more about why you may have been refused and the next steps you should take.

Maintenance records

You need to keep a record of the checks you have completed and when you had your tank emptied for your own purposes and in case you are asked for the records by Natural Resources Wales or a prospective house buyer.

Records must be kept for 5 years.

Download our maintenance guide and log book

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