WASTE WATER 

Onsite wastewater treatment and disposal

Local government assesses proposed systems for the onsite treatment and disposal of wastewater and inspects them prior to use.  

Parts of Carnarvon are connected to 'Deep Sewerage' whereby sewage goes through underground piping to the wastewater treatment plant operated by the Water Corporation. South Carnarvon, East Carnarvon and other areas are unsewered and rely on onsite treatment and disposal systems.

Onsite wastewater systems are typical of one of two main types: septic systems and aerobic treatment units (ATUs). Septic systems combined with leach drains is the most commonly used type in Carnarvon and are typically passive without the need for electrical connections while ATUs typically require electrical installations but treat the effluent to a higher standard that allows the effluent to be safely used for surface or sub-surface irrigation. 

If you are building or need to replace your existing system you will be required to complete and submit an Application to install a septic system.

For systems treating waste for more than a single dwelling, applications are required to be authorised by the Department of Health and in most cases, the applications are made to the Local Government who forwards the application on with a Local Government Report.

Maintaining a healthy waste water system at home

In the kitchen: Keep fats, oils and food scraps out of the drain as much as possible. Fats and oils can clog your effluent disposal area, contribute to bad odours and stick to the drains. Food scraps require a longer breakdown process than is provided in sewage treatment systems. Scrape plates before washing. Collect fats and oils into suitable receptacles and dispose of in the general rubbish once cool or give to an oil recycler. Food waste disposal units/grinders are not recommended. If you can’t compost your food scraps, dispose in the appropriate rubbish bin.

In the laundry: Spreading out your loads over the week can even out the wastewater volume loading and waiting for a full load can help reduce washing machine effluent. Sodium percarbonate is a septic-friendly oxidizer and sanitiser for clothes washing with temporary effectiveness after mixing with hot/warm water before breaking down to harmless byproducts compared to chlorine-based bleaches.

In the bathroom: Put only human waste and toilet paper into the toilet. Do not dispose of sanitary wipes, napkins or nappies into the toilet as they will not break down in the system. This also applies to so-called flush-able wipes, which have been found to be the most common non-soluble object causing problems in septic tanks. Leaking taps and toilet cisterns can overload the on-site sewage system over a period of time if not attended to.

Keep out harsh chemicals: Your system relies on bacteriological breakdown of sewage to function effectively. Use anti-bacterial products sparingly and avoid harsh chemicals such as drain cleaner. Mop water can be emptied into the yard away from plants and drains. Sodium percarbonate has many septic-friendly cleaning and disinfecting uses.

Caution against concreting or building over: The system needs to remain accessible for servicing and pumping out every few years or in the event of a malfunction. Structures with 4 walls or that otherwise obstruct access may not be built over the system. It is best not to concrete over any of the drainage plumbing but as a minimum avoid concreting over the septic tanks, drain inspection openings or leach drain area.

Caution against concreting or building over: The system needs to remain accessible for servicing and pumping out when required or in the event of a malfunction. Structures with 4 walls or that otherwise obstruct access can not be built over the system. It is best not to concrete over any of the drainage plumbing but as a minimum avoid concreting over the septic tanks, drain inspection openings or leach drain area.

For further information, contact the Shire office (08 9941 0000) or your local plumber.

Maintaining your septic tank and leach drain system

Alternate your leach drains: Your leach drains are of the alternating type. A diverter is in place to allow the drainage to be diverted from one leach drain to the other. Know where your diverter is located and ensure the leach drains are alternated every 6-12 months to give the soil time to recover and aerate. The lifespan of the leach drains will be improved by regular alternation of drains. If your property is rented out, it is best to provide this information to the tenant or to make other arrangements for the regular alternation of drains.

Be careful with tree roots: Trees can assist in effluent disposal by taking up the nutrients and water creating vigorous growth but in some cases they can block the drains and pipes causing a blockage.

Do not pave or seal the ground above leach drains: Leach drains need to be accessible for inspection and maintenance.

Avoid driving over leach drains: Leach drains work better when the soil isn’t compressed by driving over. Uncompressed soil allows for a soil evaporation effect. Driving over can also crush the drains if they aren’t of ‘trafficable’ construction.

Tight-fitting lids on septic tanks: The septic tank is an anaerobic system which works best without UV light and fresh air. Additionally, a lot of mosquitoes can breed in septic tanks if they can get in. Ensure all openings are tightly capped and air vents sealed with insect proof mesh.

Maintaining your effluent pump-tank

Your system includes an effluent pump-tank. This means the effluent is not gravity fed to the infiltration area and it requires a power source to pump the effluent away. A red warning light will be fitted near the septic tank to warn of a high-water level (e.g. pump failure). If the warning light flashes or is on, call a plumber. In the event of a total power outage, the warning light might not come on despite the pump-tank not working.

Maintaining your aerobic treatment unit (ATU) and effluent irrigation system

ATU treat sewage to a higher standard than septic tanks but require additional maintenance and a constant power source. Owners of ATUs are required to have arrangements in place for the regular servicing/maintenance of the unit (and irrigation system) by a qualified person (usually every 3 months).

Garden irrigation: Because they meet a higher level of treatment and include disinfection, ATU’s allow for irrigation of the effluent on or above ground level or subsurface drip irrigation depending on the approved installation. This can assist in watering and fertilizing of trees, gardens and lawns. Effluent irrigation lines need to be maintained to allow enough infiltration area for the proper disposal of the effluent without causing ponding or waterlogged conditions.

Refer to the operation manual which should be provided with your ATU system for detailed information from the manufacturer and installer about your specific system.

Useful Links

Apply to install a wastewater system