Bega Valley Shire Council | Dye Testing in Merimbula Bay

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Dye Testing in Merimbula Bay - August 2017

Bega Valley Shire Council will carry out dye dispersion tests in Merimbula Bay in August, weather permitting.

With Council commencing an environmental assessment process and developing a concept design for the Merimbula Sewerage Treatment Plant (STP) Upgrade and Deep Water Ocean Outfall, the testing is critical to the hydrodynamic modelling for the project.

Council’s Water and Sewerage Services Manager, Jim Collins, said Council is acting on advice from the NSW Environment Protection Authority and also local community concerns, that the existing beach-face outfall at Merimbula STP is not sustainable.

“The information we receive from these tests will show the dispersion rates and travel times of waterborne materials in the bay, and will help our designers determine the best location for the placement of the deep water ocean outfall,” Mr Collins said.

“The process will involve Council’s consultant hydrologists releasing a harmless, bright red fluorescent dye called Rhodamine into the water at up to four locations in the Bay, including Haycock Point (east and north) and Merimbula Embayment.

“The exact timing of the testing is dependent on weather and ocean conditions; however Merimbula Bay will be open and safe for all water users during the tests.

“Rhodamine, which will disperse rapidly, follows the pathways of currents closely and has a low impact on water quality. It will be used to measure how long it takes the currents to move water between predetermined sampling sites, with the testing set to take a few hours in each location,” Mr Collins said.

Photograph: Merimbula Bay looking south towards Pambula Beach and Haycock Point with the Pambula Merimbula Golf Course and Merimbula Sewage Treatment Plant in the foreground.

Category : Fieldwork

Created On : 21 October 2017

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FAQs

Originally the outfall extended out into the ocean and beyond the waves, but it was destroyed by a large storm in the 1970s. Since then, the beach-face outfall has been discharging effluent at the centre of Merimbula Beach. The effluent flows across the beach and into the ocean waters of Merimbula Bay.

Effluent (treated sewage) is either reused or disposed of. Council reuses as much effluent as possible for irrigation at Pambula Merimbula Golf Course and farmland at Oaklands. The remaining effluent is disposed using either the dunal exfiltration ponds or the beach-face outfall.

The beach-face outfall has caused community concern around its impact on the aquatic environment and public health. In 2009, the EPA required Council to start investigating better disposal options. After investigating a wide range of options, Council assessed the options with a community focus group made up of state government, interest groups and local community members.

In 2013, the group and Council agreed a deep ocean outfall is the preferred effluent disposal option. Compared to other options the deep ocean outfall has:

the greatest environmental benefit through improving water quality and ecology
least construction and operational impacts recognising the value the Merimbula community places on its beach and ocean fronts
is more socially, environmentally and economically sustainable in the long term.

Link to information about the discounted options: Fact Sheets 1 - 16 Merimbula Effluent Options Investigation (BVSC & AECOM 2013)

As a result, the EPA amended Council's operating licence for the STP to include a requirement to construct a deep-ocean outfall and upgrades to the STP.

First, the Community Working Group must help the project team assess options for upgrading the STP and select an alignment for the deep ocean outfall. After that, the project team will be able to design this infrastructure and prepare an environmental impact statement (EIS). This design and EIS will be subject to statutory and regulatory approval which we hope to have by 2019. Once we have approval, we will be able to seek funding for detailed design and construction.

This project will be assessed as State Significant Infrastructure (SSI) and will meet the Secretary’s Environmental Assessment Requirements (SEARs).

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Merimbula Sewage Treatment Plant Upgrade and Deep Ocean Outfall