Rural Drainage

In many rural areas there are no main sewers. Sewage has to be disposed of in other ways. There are various systems in use such as cess pits, septic tanks and mini treatment works.

Septic Tanks - What is a Septic Tank?

A septic tank treats domestic sewage and discharge, either into a watercourse or into the ground. In septic tanks the solids in the sewage settle to the bottom. Relatively clear liquid is left which forms a layer of scum on its surface. Bacteria feed on this liquid and digest some of the matter in it. The liquid then either passes into another settlement tank before passing to a watercourse or is discharged underground through a network of pipes to filter through the soil. Septic tanks are capable of treating all of a household's domestic sewage. However, the solids that build up at the bottom of the tank do need to be pumped out about once a year.

Whose responsibility is it to maintain the septic tank?

If the tank serves only your house then you alone are responsible for maintaining and emptying the tank. If several houses share the tank then the responsibility is normally shared between the owners.

If you rent your house privately, either you or your landlord may be responsible. We advise you to check your tenancy agreement to see who is responsible.

Contaminated Septic Tanks

The process of digestion in the septic tank is done by bacteria. These bacteria can be killed by certain chemicals. Too much bleach, detergents and other household chemicals may destroy the useful bacteria. As a result the sewage will not be treated fully and may cause pollution problems. Emptying the septic tank regularly will ensure the septic tank keeps working properly.

Who to Contact for Tank Emptying

Most companies who will empty your tank can be found under Waste Disposal Services in the Yellow Pages.

Watercourse Pollution

If a septic tank is too small for the amount of sewage it takes and discharges to a stream or river it may be causing pollution. See "Discharge Consents".

Cess Pits

A cess pit is simply a sealed storage tank into which sewage is drained until it can be taken away by a tanker. The sewage is not treated in the tank. Older cess pits are usually cylindrical pits lined with either brick or concrete. Modern cess pits are made from fibre glass, steel or polyethylene. Current building regulations require cess pits to be able to hold at least 18,000 litres of sewage. It is estimated that each person produces 115 litres of sewage a day. For a family of four this means that the tank will need emptying about once a month.

Blockages

Blockages can occur in the pipes leading to the tank. This can cause sewage to back up the pipe and stop the toilet working properly. The pipe leading from the tank may also become silted and then block. This will prevent the tank from working properly and cause it to fill much faster. When such blockages occur the pipes will have to be rodded or jetted.

Leaking Tanks

Old brick tanks and cracked glass fibre tanks will sometimes let ground water in. This often happens during the winter when the water table is higher. The extra water means that the tank will have to be emptied more frequently. The faulty tank will also allow sewage to leak outwards. It is an offence to allow a tank to overflow and the Environmental Protection department at the District Council may legally require that the tank be repaired or emptied.

Mini Treatment Works

In poorly drained areas (eg. on clay soils) it may only be possible to discharge to a local watercourse. As there are strict controls on the quality of effluent that is allowed into watercourses, a greater standard of treatment is required. Mini treatment works or biodisc machines act in a similar way to septic tanks. They contain motorised plastic discs which rotate through the sewage. The action of the discs encourages much more bacterial breakdown and treats the sewage to a much higher degree.

Discharge Consents

If your tank discharges its final effluent to a watercourse you will need to obtain a Consent for Discharge from the Environment Agency (EA). The EA sets standards for quality of effluent that can be allowed to enter rivers and streams. The quality of watercourses is monitored by the EA and they may take legal action against anyone who causes pollution.