'Concrete corrosion' fears as high salinity destroys 150yo mangroves

A long-awaited meeting has been held with South Australian government officials as fears mount that an ecological disaster north of Adelaide, which has already killed sensitive mangroves, could eat into the septic tanks and foundations of people's homes.

Key points:

The impact of a plant die-off at St Kilda is believed to have grown to 193 hectares Town residents are worried about high salt levels in the ground having a corrosive effect on infrastructure State government department officials have met with the local council and stakeholders over rising concerns

Late last year a salt mining company near the town of St Kilda reinstated a pump against the terms of its tenancy and filled dried out gypsum ponds with hypersaline water.

Some 10 hectares of nearby mangroves are now considered completely dead, along with 35ha of salt marsh, and lead researchers believe the evidence of stressed, dying or dead vegetation can be seen in a 193ha area.

"If you have a high pond, and a tree 150 metres away that died because it put its roots into the hypersaline water directly below it, then you can fairly safely assume there is contaminated groundwater for the intervening 150m," said environmental consultant Peri Coleman.

She said hypersaline water had leaked through cracks in the pond's gypsum lining before seeping into the surrounding marshlands and mangroves — most of which were nearly 150 years old — and marshlands.

The St Kilda mangroves have died due to hypersaline water leaking into the surrounding marshlands.(

Photo: Alex Mausolf

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Impact area spreading

Representatives from the Department for Energy and Mining (DEM), Department for Environment and Water, and the Environmental Protection Authority (EPA) on Monday night met with the City of Salisbury and stakeholders to receive an update on the situation from Ms Coleman.

Ms Coleman said township trees on the southern side of St Kilda's Mangrove Street were among those impacted by the leakage last year.

"But since Christmas the trees on the northern side of town became impacted as well, including a large gum tree up at the northernmost end of town," she said.

A DEM spokesperson said the government was working with the pond operators, Buckland Dry Creek, to "restore and maintain the stability of the site and allow for the right conditions for the rehabilitation of the impacted area".

"Analysis of piezometer data is showing positive progress but further monitoring is required to confirm that this pattern is maintained," the spokesman said.

"The government is aware of community concerns relating to trees within the St Kilda township and is committed to investigating potential environmental impacts."

What was previously a lush matt of samphires is now almost completely dead.(

Supplied: Chad Buchanan

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Salt corrosion

St Kilda and Surrounds Development and Tourism Association president Lindsay Virgo says the pollution may have increased the already high salt levels in the area's soil to corrosive quantities.

He said it was well known that the concrete kerb along St Kilda Road near the salt pans fell apart and "basically disappeared" several years ago due to the ground's salt content.

"The salinity level of the ground obviously has an effect on a concrete product, but if the salinity level is going to increase, then what is the next step?" Mr Virgo said.

"Every house around here has a concrete septic tank, and you've got footings on houses, concrete blocks that are supporting some of them, concrete slabs that have gone down for some of the newer houses.

"This is not going to have a happy ending by any means."

The DEM spokesperson said its website offered regular updates and information regarding the Dry Creek salt fields. 

Calls to expand testing

City of Salisbury deputy mayor Chad Buchanan said that while the EPA had installed groundwater testing instruments around the direct kill zone, more needed to be done.

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"We need DEM to widen the groundwater testing area and require the operator to do this as a matter of urgency because that's how we're going to fully understand and know what the wider impact is," he said.

Mr Buchanan said that while the leakage had stopped for the moment, there was a real concern about lagging salinity making its way into the groundwater.

Ms Coleman said the ponds remained a risk.

She said that the pond operators had since pumped water "from one side of the pond to the other so it would evaporate", but it had left high deposits of salt on the bed.

"That's now waiting for the next time that evaporated water comes back as rainfall and we'll have brine again," Ms Coleman said.

She said the ponds should be capped and a hypersaline-tolerant plant community established on top of them.

Ms Coleman said the plants would use the rainfall and prevent much of it from reaching the salt trapped under the soil.

"A lot of pollution control is about managing the concentration and speed of the impact," she said.

(Originally posted by Sutton)