A common problem in Northland is that many holiday homes are used for only short periods of time, during which there are often many people in residence. When large numbers of people stay at holiday homes, they can exceed the capacity of the on-site effluent treatment and disposal system, resulting in poor effluent treatment and possible failure of the disposal system. This can lead to the contamination of ground water, streams and coastal water, particularly where there are a number of holiday homes located together, all or many of them with poorly operating on-site effluent systems.
Shock loading happens when a sudden and large volume of effluent enters a treatment system that is not big enough to cope. This normally results in excessive solid material being washed out of the septic tank into the disposal system, or in AWTS type systems, entering the other treatment chambers and significantly reducing the treatment capacity of the system. The consequent failure of the disposal system can really spoil a holiday!
The simplest solution to this problem is to ensure that your system is large enough to cope with the number of people that would normally occupy the house at any one time. Alternatively, you can limit the number of occupants at the holiday home, particularly if you are renting it out.
The standard-size septic tank (4,500 litres) is generally sufficient to provide adequate treatment for up to eight people under normal operating conditions. The number of people the septic tank can handle can be increased by desludging the tank each year.
If your septic tank does not have an effluent filter fitted to the outlet, then installing one will reduce the risk of your disposal system failing during long periods of intensive use.
Aerated Wastewater Treatment Systems (AWTS)
If you are installing an AWTS in a holiday home, then you will need to check with the system’s manufacturer or supplier to make sure it is appropriate for your particular situation. You should also check that the size of the first tank (which acts as a septic tank) is sufficient for the number of people that would normally use your holiday home. If not, a simple cost-effective solution may be to install a standard septic tank before the AWTS.
The aerobic bacteria in an AWTS need a regular source of effluent to maintain their population. When an AWTS receives effluent after a long period of non-use, there will initially be too few aerobic bacteria to effectively treat the effluent. This will increase the risk of the final effluent filter or disposal system becoming clogged, especially if it is using irrigation lines, and may cause odour problems. This initial period of inadequate treatment will also reduce the environmental protection that these systems are installed to provide.
It is a good idea to have someone use the house for a few days prior to a large number of guests arriving so the bacteria have a chance to become active and increase their numbers. This simple practice will help the AWTS to treat the effluent more effectively and reduce the potential for major problems.
Make sure that your AWTS has a power supply at all times and is switched on even when the holiday home is not occupied, as this is essential to keep the aerobic bacteria alive.
If you have any questions regarding AWTS or other mechanical treatment systems, please contact the Northland Regional Council for advice on 0800 002 004.