The possibility of contaminated mine water polluting groundwater across the southern Mallee was raised at public hearings in Swan Hill in the past week.
Expert evidence has continued at the hearings into a proposed mineral sands and rare earths mine on cropping country across the Cannie Ridge, near Lalbert in Victoria.
A government inquiry today begins its third week of investigations into the planned mine which has been opposed by grain farmers and several environmental groups.
The Mallee mine hearings will run for 21 days across six weeks.
Experts for VHM Ltd said highly saline groundwater was found about 30 metres below the proposed mine site during several years of monitoring.
They also said the groundwater travelled very slowly to take thousands of years to travel about 50km to empty at the hyper-saline Lake Tyrrell, just north of Sea Lake.
VHM Ltd wants approval for an open cut mine to extract hard-to-find minerals - neodymium, praseodymium, dysprosium and terbium - which are necessary to create the magnets critical for the renewable industry.
VHM is gearing up to begin construction of the mine later this year.
Opponents say the mining could also lead to contaminants filtering into the the groundwater below the mine site or from the tailings.
Although the hearing was told there were "no registered bore users within 50km in the down gradient direction".
The freehold land has already been bought from willing sellers for its Goshen mine which covers about 1534 hectares.
VHM's flagship Goschen project will mean 20-25 years of round-the-clock mining to open cut five million tonnes of mineral sands and rare earths every year.
VHM intends to run a water pipeline 38 kilometres from Kangaroo Lake to the Cannie Ridge mine, build a generator-driven power station, upgrade some local roads and prepare its truck convoy route from the mine to the closest rail at Ultima.
Mine Free Mallee Farmers intends to call its own hydrology expert, Dr Phillip Macumber, to question the mining company's findings later this week.
Dr Macumber is well known for his extensive work on salinity in the Kerang region.
The Environment Protection Authority will continue its evidence on Tuesday with locals councils and the Victorian Farmers Federation scheduled to make presentations on Wednesday.
A site visit to VHM's Kerang warehouse is planned for Friday.
The public exhibition of its 4000-page environmental effects statement was a major milestone for the project and forms the basis of these planning panel hearings.
After that, a positive ministerial assessment for Goschen would allow VHM to apply for its relevant permits and mining licence, which is already underway, so the company can make its final investment decision.
The panel is to provide its report within 40 days after those hearings.
There is no timeline on the government's final decision for the project.