Effluent Management Report

If you want to build on a property not connected to the town sewer, you will have to install an onsite wastewater or effluent management system to treat the grey and blackwater produced in your household. Blackwater is the wastewater from your toilets, while greywater comes from your laundry, shower and sinks. Both are categorised as wastewater. There are many different onsite wastewater management systems available. The most appropriate system needs to be designed.

Overview of onsite wastewater management systems

Onsite wastewater designs can be categorised into three treatment systems (primary, secondary, and tertiary) and three disposal systems (soil absorption, subsurface irrigation and surface irrigation).

Treatment types

Primary systems treat the wastewater the least of all system types. They typically separate solids and liquids through flotation and settlement and dispose of the liquids without further treatment. Primary systems include septic tanks and composting toilets.
Secondary systems also separate solids from liquids but aid the decomposition of the solids by exposing them to air and biological processes and treating the liquid to a safe standard for irrigation on your property. Secondary systems include aerated wastewater treatment systems.
Tertiary systems use the same processes as secondary systems but also use other processes, such as membranes and UV disinfection, to treat the wastewater to an even higher standard. Tertiary systems include advanced aerated wastewater treatment systems and systems with membrane filtration or UV disinfection.

Disposal types

Wastewater systems with a primary treatment (e.g., septic tanks) require soil absorption at at least 300mm below the surface. Soil absorption systems must be sited at a lower elevation than the septic tank as they are gravity operated. This type of disposal is only suitable where the soil profile is deep enough and does not work for properties with shallow bedrock or low soil permeability (i.e., the ability of the soil to move water around). Examples of soil absorption include absorption trenches and beds and sand mounds.
Wastewater from secondary treatment systems using biological treatments may be disposed of in a subsurface irrigation system. In subsurface irrigation systems, the filtered wastewater is applied to the land under the surface to the roots of plants through a network of pipes. Plantings and microorganisms in the soil work as a filter and reduce the amount of nutrients and bacteria before the irrigated water runs into the groundwater. The design of subsurface irrigation systems depends on the amount of wastewater, the available irrigation area, and the soil texture. Subsurface irrigation systems can include raised evapotranspiration absorption beds (ETA/ETS).
Surface irrigation is only possible for wastewater treated in secondary and tertiary systems such as aerated wastewater treatment systems (AWTS) and advanced systems with membrane or UV filtration. Surface irrigation systems pump the treated wastewater to a network of drips or sprinklers above the ground where plants take it up. Currently in New South Wales, Local Government has stated they are not going to approve surface irrigation systems due to the high levels of failure (2021).

Stormwater modeling

Water NSW has a requirement that the Consultant that design the Onsite Wastewater systems in the Sydney drinking water catchment area, is required to supply a certificate or report for stormwater modelling.

For developments of less than 2,500m2: S3QM Model

S3QM is a small-scale stormwater model as a complying tool for the development application. WaterNSW has determined two critical requirements for managing stormwater in the Sydney drinking water catchment area.

  • BASIX, the Building and Sustainability Index, require new homes to be water and energy efficient.
  • NorBE, the neutral and beneficial effect on water quality must be met to achieve higher standards using more landscape treatment measures than the BASIX required.
S3QM estimates stormwater pollutant generation and the performance of stormwater treatments from smaller, less complex proposed developments. WaterNSW accepts the use of this tool when estimating stormwater impacts for smaller developments of less than 2,500 square metres. In estimating impacts, the modelling allows for the design of the technical intervention that will achieve improvement of water quality, e.g., grassed areas and water tanks

For developments of more than 2,500m2: Model for Urban Stormwater Improvement Conceptualisation (MUSIC)

Described by WaterNSW, MUSIC is a water quality decision support tool for stormwater managers. It helps the planning and design (at a conceptual level) of appropriate stormwater treatment and management systems from individual development to a catchment level. MUSIC provides information on whether a proposed stormwater management system conceptually would achieve water quality targets, and in the Sydney drinking water catchment, whether the NorBE (Neutral or Beneficial Effect on Water Quality) requirement is satisfied. At CESsoils, we have a license for the tool and qualified trained professionals who can utilise this system for proposed urban and rural land use developments greater than 2,500 square metres.