Content provided by Canterbury Regional Council
Failing to ensure that septic tanks are properly maintained could put users’ health at risk.
It is estimated that there are about 34,000 onsite wastewater systems, often called septic tanks, across the Canterbury region alone. It’s a relatively high number when considering that Auckland, with nearly three times the population, has an estimated 46,000 septic tanks.
The most common system for single households in Canterbury is a primary treatment tank and land application system (i.e., a bolder pit or trench), but there are also some newer secondary treatment systems.
If these systems aren’t looked after properly, there could be serious consequences. Faulty systems can contaminate the land on individual properties, and even the drinking water supplies of the whole community.
Is onsite wastewater causing illness?
When it comes to health risks from onsite wastewater, prevention is key. Canterbury Regional Council (Environment Canterbury) Resource Management Technical Lead Jessica Newlands warns that problems often begin when people don’t maintain their systems and the tank or gully trap overflows, causing ponding of wastewater on the land surface.
‘There’s a heightened risk in areas where the ground has had “human interference”, such as landscaping, vehicle movements or the installation of children’s equipment,’ she says.
Bronwyn Humphries, Senior Groundwater Scientist at Institute of Environmental Science and Research (ESR), agrees, highlighting anecdotal evidence linking seepage with children’s play areas.
‘Kids might just assume it’s a muddy puddle, and not bother to tell their parents,’ Humphries says. ‘There was a case in Canterbury where children had sustained gastro for two years before the family finally figured out the kids were playing in a waste disposal field near their playground. It can take people a long time to realise something is wrong.’
Onsite wastewater can also enter groundwater, from which much of Canterbury’s drinking water is sourced. Weather can exacerbate the issue; prolonged dry periods followed by heavy rainfall events can cause wastewater to rapidly infiltrate groundwater, significantly increasing the risk of contamination.
Sucking out the sludge
In a bid to understand some of the key issues around onsite wastewater, ESR reached out to a sludge-removal company and asked them to log their jobs for a week.
The predominant problem was people not routinely getting the sludge sucked out every three years, as recommended. Instead, some were waiting up to 10 years to get it done. Newlands says this ‘flush and forget’ mentality is concerning.
‘For every year that you don’t look after your tank, you’re increasing the risk that something will go wrong.’
She says it is important that people do their research when purchasing a property with an onsite wastewater system.
‘Often, when a rural property changes hands, the new owners have no idea what sort of system they’re getting, where it is located, or when it was last serviced. Real estate agents and lawyers are not legally required to disclose the type of system and the service history, so the impetus is on the property owner to find out all they can about the tank – including whether a resource consent has lapsed.’
Spotting the signs
Signs of potential problems could include water presenting at the surface and offensive odours – often a strong ammonia or sewage-type smell.
Throwing bleach or antimicrobial cleaning products down the toilet is a big no-no, as it kills off the ‘good’ microbes that help to break down the sludge. Newlands says only the three ‘P’s should be flushed: pee, poo and paper.
‘Other items can cause blockages and added maintenance costs,’ she says. ‘Wet wipes and sanitary items should be put in the rubbish.’
Maintenance is key
Regardless of whether onsite wastewater systems are new or old, keeping them well maintained will help ensure any problems are caught early. This reduces the risk of wastewater systems causing community contamination events, such as wastewater contaminating downgradient drinking water wells. According to Humphries, maintaining wastewater systems also prevents a system failure that can require a complete renewal, which can cost between $30,000 and $40,000.
‘Enteric (occurring in the intestines) illnesses stemming from drinking water supplies that are contaminated by wastewater can include norovirus, which may leave you unwell for several weeks. Longer illnesses are also possible due to pathogenic organisms like cryptosporidium and giardia,’ says Humphries, highlighting that the cost to public health can be significant when things go wrong.
Key tips for managing wastewater
- Newer, secondary treatment systems require regular inspection and maintenance at least every 12 months, including sludge removal every three years. Older, primary treatment systems (septic tanks), while not requiring an inspection, still need to have sludge pumped out around once every three years.
- Residents with onsite wastewater systems can support microbial communities by using low-phosphorous soaps and detergents, and not flushing solids, such as wet wipes, or aggressive chemicals like caustic soda. Water New Zealand has more information on what can and cannot be flushed, and other advice for taking care of onsite wastewater systems.
- Residents should try to space out water use to avoid overloading the system – for example, not running a washing machine and a dishwasher at the same time.
- Systems should be inspected immediately by a suitably qualified technician if there are issues like sewage overflow, murky or smelly puddles around treatment systems, or even a broken tank lid.
- Residents should be advised that before purchasing a property with an onsite wastewater management system, they should check with a lawyer or estate agent to find out whether the system is consented, and how it has been maintained.