Coliban Water is seeking approval to construct a brine lagoon at Epsom in a bid to prevent rising groundwater – laced with hydrogen sulphide, arsenic, dissolved salts and other metals – spilling into waterways in and around Bendigo.
Known as the ‘Coliban Option,’ the $1.3 million, 270-megalitre, brine lagoon is a temporary fix while authorities seek a permanent solution as water continues to fill abandoned mine shafts beneath the city.
If left unchecked, rising groundwater could damage roads, footpaths and buildings and threaten the operations of the one of the city’s major tourist draw cards, the Central Deborah Tourist Mine.
Its impacts on the environment, agriculture and public health are also far-reaching.
In its submission to council, Coliban warns the discharged mining water would lead to increased salinity in the wider Murray-Darling Basin and pose “public amenity issues”.
Part of the project was submitted to the City of Greater Bendigo for approval earlier this month and Coliban has told council the lagoon must be operational by the end of July.
"The critical requirement of the project is that it must be operational by 31 July, 2016,"Coliban Water submission to council
The Coliban Option would see the construction of a pipeline from Eaglehawk to the Epsom Water Reclamation Plant, where the brine lagoon would be constructed.
Department of Environment, Land, Water and Planning Loddon Mallee regional director Graham Phelps told the Bendigo Advertiser if the Coliban Option was found to be feasible and given ministerial approval, the water would be treated to remove contaminants.
“If possible, clean water would be re-used or returned to the environment,”DELWP Loddon Mallee regional director Graham Phelps
“The Coliban Option is based on the preferred option of the Community Reference Group and has been endorsed by the State and Local Government Advisory Group,” Mr Phelps said.
“If approved it would address the groundwater issue over the next five years while a permanent solution is developed.”
A DELWP commissioned report published last year warned water below the city was rising to levels seen almost five decades earlier, when mine water flowed freely into the Bendigo catchment.
“Without intervention, uncontrolled discharge of mine water to the environmental appears to be imminent,”2015 DELWP commissioned report
“This will result in groundwater flowing into Bendigo Creek and other waterways as it did in the 1970s and 1980s.”
The threat of rising groundwater became a problem for the city when Unity Mining closed its Kangaroo Flat mine in 2011 – ending the latest phase of mining in a history dating back to the gold rushes of the early 19th century.
In early 2012, Unity Mining switched off the groundwater pumps which had funnelled water into evaporation ponds at Woodvale for decades, allowing its mines to remain operational.
The DELWP commissioned report said once this process – known as mine dewatering – ceased, the “extensive network of interconnected mine voids below Bendigo” began filling as groundwater drained through rock fractures and historical workings.
The report raises concerns about arsenic and hydrogen sulfide – otherwise known as ‘rotten egg gas’ – in the rising mine water.
“Compared with waters typically flowing in surface waterways in the Bendigo area, the mine water is also brackish, has elevated concentrations of iron, manganese and some heavy metals [e.g. nickel, chromium, zinc and lead have all have been detected at trace concentrations],” it reads.
Faced with the threat to one of the city’s icons, the Bendigo Trust – which operates the Central Deborah Tourist Mine – continued dewatering once Unity switched off its pumps.
However in June last year the state government put a stop to the use of the Woodvale Ponds after sustained pressure from locals concerned about the effects of living near site.
Late last September, Water Minister Lisa Neville said the state government would provide $1.5 million to fund a feasibility study into the Coliban Option, pumping water into storage in the New Chum mine workings in Golden Square as an interim solution.
“[This] announcement puts us firmly on track to reach the long term solution that will permanently overcome the issues in managing rising groundwater in Bendigo,” the minister said at the time.
However, the Coliban Option is not that permanent solution – its operational lifespan is expected to be five years.
It is involves three components: a new groundwater treatment plant at the Epsom water factory, an underground pipeline and the brine lagoon. Currently, only the brine lagoon is awaiting council approval.
The Coliban Option would involve building a new underground pipeline to transfer 920 megalitres of groundwater per year from Lake Neangar to Epsom.
This transfer system would use the existing groundwater extraction system, pump and pipeline from the New Moon Mine in Eaglehawk to Lake Neangar.
Treated water from the process would be discharged into the Bendigo Creek, with the brine created from this process stored and evaporated in the proposed lagoon.
The Coliban submission to council said the Epsom site was chosen among six proposals as it did not contain any trees or native vegetation and was located further away from urban communities “to better manage potential odour”.
Mr Phelps said DWELP would engage with landowners when and if the Coliban Option was approved.
“Following the conclusion of the feasibility study and if the project is approved we will meet all planning and approval requirements which will include community engagement and consultation with stakeholders, nearby residents and business operators,” he said.
Long term solutions to Bendigo’s rising groundwater problem proposed in the 2015 report include the creation of wetlands and the use of a new generation of filters known as ‘permeable reactive barriers’.