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Molonglo Valley Interceptor Sewer Odour Control Project

Frequently Asked Questions

Background and details

The Molonglo Valley is Canberra’s newest region of urban development. Molonglo Valley Stage 1 and Stage 2 include the suburbs of Denman Prospect, Wright and Coombs, which are south of the Molonglo River. Molonglo Valley Stage 3 is the third and final stage of the development, comprising suburbs north of the Molonglo River, including Whitlam and future suburbs of Molonglo 3 east of the new John Gorton Drive. 

Figure 1: Molonglo 3 Development Area (from Molonglo Valley 3 Planning and Design Framework).

The Molonglo Valley Interceptor Sewer (MVIS) is Icon Water’s largest and most critical sewer. It contains a series of ventilation structures that were constructed some 40 years ago. The ventilation structures, or vents, protect the MVIS from corrosion through venting corrosive gases from the sewer to the atmosphere. When the MVIS was constructed there was no future residential development identified for Molonglo Valley Stages 2 and 3. Hence the impact of sewer odours from the ventilation of the MVIS on adjacent residents was not a consideration.

Why are you doing this?

The MVIS Odour Mitigation Project is one of the Suburban Land Agency’s (SLA) infrastructure projects required to enable further development in the Molonglo Valley. 

During planning of Molonglo Valley 2 and 3 it was identifed that odour emissions from the existing vents had the potential to cause widespread impacts on the future residential developments, which may lead to complaints from resident’s sensitive to odours.

To address these concerns the existing ventilation structures, such as the vent shown in Figure 2, will be replaced with more technically advanced Odour Control Units (OCUs) that will ensure the ongoing protection of the MVIS against corrosion, while ensuring that future residents are not impacted by odour emissions. The OCUs use carbon filters to remove odour from the sewer gases before they are discharged to the atmosphere through vent stacks.  



Figure 2: Photo of existing sewer vent to be removed.

The primary objective of the project is to design and construct four OCUs and ancillary works (vehicle access, landscaping, electrical supplies and demolition/removal of existing vent stacks) to reduce the extent of odour within the Molonglo Valley, whilst continuing to protect the sewer from corrosion. Following construction and commissioning the OCUs will be handed over to Icon Water to own, maintain and operate.

Modelling studies have been undertaken to determine the optimal locations of the OCUs. The proposed location of the four OCUs and the existing infrastructure to be removed (represented by the green crosses) are shown in Figure 3.

Figure 3: Odour Control Unit locations (Sites 1 to 4) and existing vents to be removed (green circles).


What will happen to the existing vent stacks?

The new OCUs will result in some existing vent stacks on the MVIS becoming redundant. These structures will be decommissioned. The existing vent stacks will be removed and the connection points to the MVIS will be closed off. An example of a vent stack to be removed is at Figure 2.

Will the work have any environmental impact?

In 2021 the Conservator of Flora and Fauna provided an Environmental Significance Opinion (ESO) on the project, which concluded the works are not expected to have a significant adverse environmental impact. The four OCU sites were carefully selected to avoid impacts to sensitive environmental sites in the region and to minimise impacts on the Molonglo River Reserve. 

The project is within the Strategic Assessment Area under the Molonglo Valley Plan for the Protection of Matters of National Environmental Significance. The Plan includes provisions for the construction of infrastructure that will be required to support development in the Molonglo Valley. 

All construction works will need to be undertaken in accordance with an approved Construction Environmental Management Plan. 

How long will the works take? Including When.

Construction works are expected to commence in mid-2022 and take approximately 12 months to complete. Construction of Site 3 and Site 4, west of Coppins Crossing Road, will commence first. Construction of Site 1 and Site 2, east of Coppins Crossing Road, will follow shortly after. 

Will this work have any impact on residents of Whitlam and Denman Prospect? 

The works are expected to have minimal impact on the residents of Whitlam and Denman Prospect. The sites are located a significant distance from residential areas and are unable to be accessed by the public in vehicles. Construction will require use of the MVIS access track, and it is expected that the track will be closed for public use at times.  

All construction works will need to be undertaken in accordance with an approved Construction Environmental Management Plan, which will ensure that dust and noise impacts are minimised.

Will the works impact on Namarag special purpose reserve? 

The works will not impact on the Namarag special purpose reserve. Careful planning has ensured that Namarag special purpose reserve infrastructure will not be adversely impacted. However, access to Namarag special purpose reserve may be impacted during construction of the sites. The SLA will liaise closely with Parks and Conversation Services to ensure that impacts are minimised during construction.