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Off the mains – treating home sewage
Is there a bad smell lingering in your backyard? One patch of grass looking particularly green? Sceptical of your septic tank?
A septic tank is opened for inspection.
If not operated or maintained properly, septic tanks and other on-site systems used to treat domestic wastewater can leak and pose a health and environmental risk.
“Poorly maintained or badly designed septic tanks can leach nutrients and bacteria into groundwater or through into streams or lakes," says civil engineer, Ian Gunn. "Of particular concern are the strips of developments along lakes where you have a whole lot of sections lining a lake shore or coastline. Often it’s the oldest properties using the oldest systems that line the lake shore.”
Septic tanks are just one type of on-site system that can treat domestic wastewater and return it to the environment within the boundaries of the property of origin. There are estimated to be around 270,000 domestic on-site systems in New Zealand. However, the performance of those systems is quite variable.
Many studies and surveys carried out in recent years reveal that a large number of on-site wastewater systems in New Zealand are not performing in a way that provides acceptable levels of treatment. Untreated or partially treated sewage from these systems is causing public health risks and negative environmental effects.
The 'sniff and look' test is one way to find out if a wastewater system isn’t working. You know there is a problem if you can see patches of wet or smell a soggy silage odour, says Gunn. Without proper maintenance such as regular pump-outs, the tank or the trenches receiving the wastewater can overflow. Also, septic tanks in baches are a common problem in the holiday season when the systems get a 'shock load'. With the sudden influx of people, bacteria can’t cope with the waste entering the system.
“Owners must also use their systems sensibly. Many councils have a user's guide about what to do and what not to do. Owners should really be reminded regularly to check their systems. Some councils send out a reminder with the rates notice,” says Gunn.
According to Gunn, people should ideally be looking at the system ahead of a problem occurring. He says some councils already encourage proactive performance monitoring, and in some areas it is recognised that regular inspections are needed to get ahead of potential problems. For example, Environment Bay of Plenty has implemented a scheme in problem areas where they check every system and pump it every three years.
The Ministry is currently scoping the feasibility of a national environmental standard that would apply to the operation and maintenance of domestic on-site wastewater systems.
If you do suspect there is a problem with your system, we recommend you contact your regional council.
For more information contact Barry Johnson, email barry.johnson@mfe.govt.nz or phone (04) 439 7769.
