Andrew Carvell, a Domestic Wastewater Management Officer with the Regional Council, says Northland’s population swells considerably over summer, particularly in popular beach areas.
In some cases, areas with a normally resident population of just several dozen can balloon to hundreds - or even thousands - of people.
That in turn puts added environmental stresses on the region, especially when many popular areas rely on septic tanks instead of a reticulated sewage treatment system.
Mr Carvell estimates there are about 18,500 “on site treatment systems” (including septic tanks) in Northland – responsible for about 35 percent of the region’s waste treatment needs.
Problems often stem from the sheer number of people using a septic system over summer, together with visitors’ unfamiliarity with septic tanks and the various practices that go with them.
Mr Carvell says although the capacity of septic tanks varies, most were never designed to deal with the situation that arises when a normal household is boosted in size – possibly several times or more – by friends and relatives who may stay for days at a time.
While people obviously need to use toilets, they can limit much of the wastewater generated in other areas – such as showering, washing clothes and doing dishes.
“Efficient use of water can go a long way to preventing septic tank overloads.”
He says overloaded on site treatment systems can cause a variety or problems, including polluting ground and surface water and affecting shellfish beds.
Effectively, a septic tank acts as a settling chamber, allowing solids to separate out from wastewater, which then goes into a soakage system in a process typically taking one to three days.
Overloading the system denies it the chance to treat the wastewater properly and can simply overwhelm soakage fields.
Meanwhile, Mr Carvell says depending on use, tanks usually need to be cleaned every three to five years to remove built-up solids as part of a routine maintenance programme.
“Otherwise solids accumulate to a level where the system doesn’t function properly and soakage fields can be permanently damaged.”
Mr Carvell says many new coastal developments boast more advanced biological treatment systems that use a range of bacteria and other organisms to treat sewage.
These effectively feed on the wastewater but can starve and die if the supply of waste is cut off for too long or if aeration systems are turned off outside of the holiday season.
“Loading biological treatment systems too heavily without allowing a start up period can lead to poor treatment of the wastewater, causing bad odour and blockage of the disposal system. “
People with these systems should be aware of their limitations and discuss any concerns with their suppliers.