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Appendix 1: Definitions

Cluster systems
On-site systems that serve two or more houses, but less than an entire community. The wastewater from each group of dwellings may be treated on-site by individual septic tanks before the effluent is transported through alternative sewer systems to a nearby off-site location for further treatment and ecosystem re-entry.
Disposal field
In most cases this comprises a subsurface 'field drain', such as perforated pipes. The idea is that the wastewater percolates into unsaturated soil at least 600 mm above the groundwater table. This way the wastewater is renovated in the unsaturated soil profile by microbial and physico-chemical processes.
Domestic wastewater
Wastewater or sewage from domestic households originating from toilets, urinals, kitchens, bathrooms, showers, baths, basins and laundries, such as from a dwelling, but excludes stormwater flows.
Environmental performance
The performance of on-site wastewater treatment systems relative to both public health protection and protection of the natural and physical environment.
Escherichia coliform (E. coli)
One of the species of bacteria in the coliform group. Its presence is considered indicative of fresh faecal contamination.
Faecal coliform
Bacteria present in waste from warm blooded animals (mammals or birds) and used as an indicator of pollution in water.
A situation where the effluent is not treated to a sufficient standard before entering groundwater or surface waters, or where inadequately treated effluent rises to the ground surface (usually near the on-site system). The failure of an on-site system may cause a risk to human health or the environment.
An area with high numbers of (failing) on-site systems within a larger area of low or normal density.
Primary systems
These systems involve separating bulk solids, grease and grit from the main liquid stream. Septic tanks are a well-known traditional example of on-site primary systems. Typical primary systems are either single-chamber or two-chamber septic tanks.
Secondary systems/ advanced on-site systems
These systems involve biological processes to biodegrade the organic contaminants in the wastewater. Secondary treatment processes can include wastewater aeration, such as aerated wastewater treatment systems (AWTS), treatment and filtering media, disinfection, and other technologies. These systems are typically designed, operated and maintained by specialist companies. The disposal field often includes dripper lines and evapo-transpiration beds. Advanced systems are generally used in more 'difficult' sites, such as in poorly drained soils, in close proximity to surface waters, or where there is limited room for the disposal field.
Liquid or solid material removed from a septic tank, cesspool, portable toilet, or similar system that receives only domestic (non commercial) waste.
Septic tank
Septic tanks comprise two distinct components: a solids settling tank (the septic tank) and an effluent disposal field. The main function of the tank is to allow solids to settle out and scum and fat to float to the surface. The liquid fraction is then drawn off by gravity from a pipe just below the surface of the wastewater. Some septic tanks have multiple chambers to improve solids removal, but the majority are simple single-chamber tanks.
The material that settles out of wastewater primary and secondary treatment systems; the solids layer at the bottom of a septic tank.
Tertiary systems
The treatment process following secondary treatment can involve the use of sand filters to further improve the removal of organic matter (fine solids) from biological secondary treatment, and the use of disinfection units to remove human intestinal bacteria before treated effluent discharge. Disinfection can be achieved for on-site treatment units via tablet chlorination or ultraviolet light units.
Also known as sewage, wastewater includes the water you flush down your toilet and the water that drains from your bathtub, sink, washing machine and many other domestic sources.