On-site systems greater than 40 equiv persons (EP)

On-site systems > 40 EP are typically installed at commercial sites, such as schools, wineries, work places, camp grounds / caravan parks and hotels.

Large on-site wastewater systems represent a higher risk than on-site systems serving single domestic dwellings, due to the exposure of third-parties to recycled water.  While the On-site Wastewater Systems Code is suitable to be used for many aspects of a design, including hydraulic and organic loading, site and soil evaluation, setbacks and land application, it does not consider the additional risk to public health associated with large on-site wastewater systems.  System designs are therefore required to contemplate risk management and multi-barrier principles, in line with the Australian Guidelines for Water Recycling (PDF 2.1MB).

The Australian Guidelines for Water Recycling require a fit-for-purpose approach to recycled water use.  Table 3.8 of the Guidelines establishes pathogen reduction targets for a variety of recycled water uses, expressed as log reductions, for the protection of public health.  A multi-barrier approach is considered necessary.

Pre-treatment barriers

Trade wastes (e.g., commercial kitchen waste) must be pre-treated via an appropriate trade waste pre-treatment device, prior to delivery to an on-site wastewater system.  The SA Water trade waste guidelines may be used to select and size an appropriate pre-treatment device.

Treatment barriers

Large on-site wastewater systems typically do not have sufficient design elements to allocate log reduction credits based on the AGWR or other published literature, such as Water Research Australia validation guidelines. There may be some cases where default log reductions can be applied to large on-site wastewater systems, however this is likely to be uncommon and would mainly apply to large systems (> 100 kL/d).  See the Recycled Water Management section for information on default log reductions for treatment barriers.

Secondary treatment systems are required to demonstrated secondary treatment by on-going water quality testing, reported via an annual report.  This is not required where recycled water is disposed of sub-surface. 

Primary treatment systems are to meet the requirements of the On-site Wastewater Systems Code.

On-site preventative measures

Large on-site wastewater systems will typically have all log reduction credits applied to non-treatment barriers, also known as on-site preventative measures.  On-site preventative measures must be reliable, practical, and easily controlled.

An example of how log reduction credits may be allocated for spray irrigation of a designated land application area or fenced woodlot is shown below:

An example of how log reduction credits may be allocated for spray irrigation of a designated land application area or fenced woodlot
Category Barrier Virus Protozoa Bacteria
Wastewater treatment Secondary treatment and chlorine disinfection - - -
On-site preventative measures No public access during irrigation (e.g., fenced irrigation site) 2 2 2
On-site preventative measures No public access after irrigation (e.g., fenced irrigation site with signage) 1 1 1
On-site preventative measures Buffer distance > 25m 1 1 1
On-site preventative measures Spray drift control (inward throw sprinklers, low throw, large droplet, or low height risers) 1 1 1
Total log reduction value (wastewater treatment + on-site prevention)   5.0 5.0 5.0
Total log reduction required (AGWR 2006)   5.0 5.0 5.0

Guidance on applying log reduction credits for on-site preventative measures can be found in Table 3.5 of AGWR. 

Note that the use of recycled water from a large on-site system is unlikely to be suitable for:

  • Municipal irrigation (e.g., public oval or park) — The maximum log credits able to be applied to on-site preventative measures for municipal irrigation is 4.0, resulting in a 1.0 log shortfall.
  • Commercial food crops — The maximum log credit applied to the drip irrigation of raised crops with no ground contact (e.g., apples, apricots, grapes) is 5.0, resulting in a 1.0 log shortfall.

Note that for systems disposing of treated wastewater subsurface, log reduction credits do not need to be considered.

Risk management plan

By default, a Risk Management Plan is required for all large on-site wastewater systems with surface irrigation.  Contact the Wastewater Management team to discuss exemptions.

Maintenance and monitoring

Approvals for large on-site systems may include conditions relating to:

  • on-line flow, level and aeration monitoring
  • land application monitoring (visual inspections)
  • servicing system components
  • maintenance of pre-treatment devices
  • de-sludging primary treatment tanks
  • water quality monitoring.

Engineering certification

Engineering certification is often required for large on-site systems, particularly if located in an environmentally sensitive area or a complex system.  It may not be required for straight-forward systems located outside of an environmentally sensitive area, and using an SA Health approved product.

SA Health approved products do not need to be selected for use, although they may be, where appropriate.