Bowral Sewage Treatment Plant Upgrade

  • Project typeUpgrades to Bowral Sewage Treatment Plant
  • Contractor nameHaslin Constructions Pty Ltd
Burradoo STP
Update on progress of Bowral Sewerage Treatment Plant (STP) - February 2024

Sewage generated within Bowral, East Bowral and Burradoo is transferred through a combination of gravity sewers and sewage pump stations to the Bowral Sewage Treatment Plant (STP).

Although the STP is operating well and the quality of the effluent discharged to the Wingecarribee River within its Environment Protection Licence, the plant is now operating at near its design capacity. A further upgrade of the STP is required to:

  • improve process and operational performance;
  • provide treatment capacity to meet current and future population demands in the catchment;
  • provide treatment infrastructure to meet environmental objectives from the regulator - the NSW Environmental Protection Agency (EPA); and
  • protect the sensitive environment the STP discharges into which is part of the Sydney Drinking Water Catchment.


It was necessary to undertake the environmental investigations and the detailed design of the STP Upgrade concurrently.

As endorsed at the Council meeting of 13 October 2021, the (final) draft of the REF  was publicly displayed on Council’s website – for the community’s information. The REF was comprehensive document required to identify and assess potential impacts of the project. It includes extensive studies with modelling on various aspects including catchment water quality and effluent discharge impact assessment, and air quality impacts.


The design of the STP upgrade has been completed. In order to accommodate future growth, a design horizon of up to the year 2046 (which equates to a forecast equivalent population of 21,000) has been adopted for the development of the upgrade. The upgraded facility will serve our community well into the future providing resilience and a robust and reliable service.

The STP upgrade has been designed to use proven technology that creates an opportunity to enhance water quality in the Wingecarribee River. Together with designing for key attributes such as hydraulic requirements and reliable and efficient operations, the design will ensure that there are ‘neutral or beneficial effects’ to the receiving waters that the STP discharges to.

The STP upgrade design provides improvements to each step within the STP treatment process as well as further treatment steps, from the receival and screening of raw sewage to the discharge of high quality effluent off site, and the handling and disposal of sludge/biosolids from the site.

The design has been undertaken in a way to balance stringent water quality (effluent discharge) requirements, construction and operational cost factors (i.e. whole of life costs).

Key findings of the REF

The necessary investigations to allow for the environmental assessment of the project been undertaken over several years, liaising with regulatory stakeholders whose requirements have influenced key decisions in the design development. Information regarding regulatory requirements and their associated influence on key decisions is shared in the (final draft) REF.

The REF has been prepared in two parts – with the main document being for the proposed STP upgrades on the existing site, plus an addendum for the upsizing of the incoming main (where it crosses Mittagong Creek prior to entering the STP site).

The key findings of the REF is that it is unlikely that there would be significant adverse environmental impacts associated with the Bowral STP Upgrade project. Although there is a focus on effluent discharge catchment impacts, as the STP is in close proximity to residential areas another project priority is reducing the risk of odour emanating from the STP. The design has addressed this issue by several operational changes, and the incorporation covers and odour control biofilters to the inlet works.

The Odour Impact Assessment modelling indicates that odour concentrations are predicted to decrease by an average of 62 per cent across the sensitive receptors under normal operations – therefore providing a healthier and cleaner environment for our neighbouring residents.

Project timeframes

Construction of the proposed upgrade works commenced in June 2023. 

Given the scope and complexity of the project, construction phase timeframes are expected to extend for 18 months to 2 years.


Following their review of the (final draft) REF document, the EPA provided concurrence to the proposed upgrade works, and in turn Council received approval from the Department of Planning & Environment approval to proceed with the construction of the proposed works. 

Construction of the proposed upgrade works on this ‘brownfields’ site whilst maintaining operation of the existing treatment infrastructure presents unique challenges, including the careful management of interfaces.

The community will be provided with updates throughout the project. As with most construction projects of this scale there will be impacts to the local community during the works. We will communicate with potentially impacted community members, with the aim to mitigate or minimise the impacts they may be subject to. 

Contact details

Project Delivery team
02 4868 0888