Cracks above Dendrobium mine spark fears for water catchment

The front gates of the Dendrobium mine at Mount Kembla last week. Picture: Adam McLean

The front gates of the Dendrobium mine at Mount Kembla last week. Picture: Adam McLean

The ground is bulging and cracks are reaching from the surface to the coal seam in a section of Sydney's drinking water catchment that sits above a mine, according to an independent study commissioned by the state government.

The findings have prompted WaterNSW to seek greater scrutiny of future mining applications.

The extensive study, by consultants PSM and commissioned by the Planning Department, found the effects of bulging - including under and around Cordeaux reservoir - "do not appear to be recognised or incorporated into modelling" by the Dendrobium underground coal mine, near Wollongong.

"Investigations at [one] site showed new cracks extended through to the ground surface and the permeability increases post-mining by one to three orders of magnitude" or as much as 1000 times, the report found.

The Dendrobium underground coal mine in the Special Areas near the Illawarra. Picture: Andy Zakeli

The Dendrobium underground coal mine in the Special Areas near the Illawarra. Picture: Andy Zakeli

The study was prompted by Fairfax Media reports in 2015, which revealed the mine's owner – then BHP Billiton and now its spun-off unit, South 32 – had secured approval for more longwall mining without submitting a water impact assessment that matched the planned mining.

The miner, which had ordered one water study but then kept its findings secret, was later granted more longwalls with the height of the seams dubbed the most aggressive by any mine in Sydney's catchment.

Environmental groups have long highlighted the subsidence resulting from the extraction of coal was clearly leading to the drainage of surface rivers and aquifers.

Those concerns were partly borne out in the 2016 Audit of the Sydney Drinking Water Catchment that was quietly tabled last month by the Berejiklian government.

So-called "trans-current shear and dilation" identified in the fracturing of the sandstone. Picture: PSM report

So-called "trans-current shear and dilation" identified in the fracturing of the sandstone. Picture: PSM report

The PSM results, though, go further than the audit.

The report found sensitive upland swamps – which are ecologically endangered and play an important role in moderating surface water flows – were being affected by the Dendrobium mine “at distances of around 250 to 900 metres” from the mining panels.

The report stressed its findings related to just the single monitoring site above the 3B area of the mine, and that “a number of gaps and uncertainties” remain. Still, the fracturing over longwall number 9 was “100 per cent of the cover”.

Dams need a review

Among its recommendations, the consultants called for a review of the water balance for nearby Cordeaux Reservoir, and a "more thorough analysis of the potential connection" between mine areas and that dam.

A dried-out creek above the Dendrobium mine in the Special Areas. Picture: Julie Sheppard

A dried-out creek above the Dendrobium mine in the Special Areas. Picture: Julie Sheppard

Similarly, it called for additional monitoring between the Area 3B and Avon Reservoir, and a review of "the potential current and future impacts of continued mining" on that dam.

WaterNSW, the government agency which manages the catchment, supported the "Height of Cracking" report and a related summary as "comprehensive and accurately" representing the state of current understanding "of this critical issue".

"WaterNSW considers the report's key recommendations should be incorporated into the assessment of mining applications," a spokesman said. (See map below of the Dendrobium longwall mines.)

'Grave' finding

Peter Turner, a mining spokesman at the National Parks Association, said WaterNSW's assessment was "very disappointing" because it failed to address the severity of the impacts raised by the PSM consultants.

Dr Turner also noted Planning had withheld the Dendrobium reports from WaterNSW, the Office of Environment and Heritage and the community without explanation for months and was still holding back two other long promised reports. A freedom of information application for two earlier reports has been refused.

"The two yet to be released reports provided the basis for the Department's December 2016 approval of two more longwall extractions at Dendrobium. Like the then new mining approved in February 2013, the recent mining was again approved without an appropriate groundwater impact assessment."

"It's now clear why Planning withheld these reports from WaterNSW, OEH and the community for as long as they could," he said.

The released reports confirm a direct association between rainfall and water inflow in all four mining areas at Dendrobium Mine.

"The catchment impacts are grave, extensive and some are much more severe than had been anticipated and warned of by the community, WaterNSW and the OEH."

Dr Turner said it was "hard to imagine a clearer demonstration that the Department of Planning values the very limited returns from the coal beneath the Special Areas far more than the integrity of Sydney's primary public health asset, its drinking water catchment".

A spokesman for South32 said it was examining the report: "We will continue to engage with government agencies and other key stakeholders to ensure continued compliance with consent conditions, to provide ongoing employment to 400 people who are part of the local community, and to continue to supply our customers with premium quality metallurgical coal".

The most recent end of panel mining report, though, put the number of staff at 265.

Fairfax Media sought comment from the Planning Department.

'Wilful ignorance'

Mehreen Faruqi, the Greens environment spokeswoman, said it was "common sense" not to allow mining in a city's catchment.

"The NSW government approving experiments in longwall mining is wilful ignorance," Dr Faruqi said. "The report shows that no one really knows how much water is being lost. This is the complete opposite of the precautionary principle."

A spokesman for the NSW Minerals Council said the PSM report "focused on one specific area of mining and the details are a matter for the company involved".

"Generally speaking subsidence prediction is good and continually improving," he said.

"The Southern Coalfield is NSW's only major source of hard coking coal, which supports the local steel industry, supports thousands of jobs and brings in billions of dollars of export income to the region and the state," the spokesman said.

Loss to come

Dr Turner said that the Dendrobrium mine's inadequate monitoring system suggested the impacts don't appear yet to have caused substantial water leakage from the Cordeaux and Avon reservoirs.

Still, "there can be no doubt losses will increase and that the approval of further mining would add to the risk of major water losses", he said.

"Infamously distinguishing it from the other mines in the Special Areas, the more than two kilometre-long longwall Dendrobium extractions 400 metres or so below the surface are exceptionally wide at 300 metres and exceptionally thick with coal seam cutting heights of up to 4.6 metres," he said.

Dr Turner said it was "bewildering" the Department of Planning could have accepted and even echoed the advice of the mining company's consultants, "that there would be no significant consequences arising from the creation of such large and extensive voids some 400 metres below the surface".

Dr Turner also expressed concern that all but one of the released reports dismissed the work that predicted connected seam to surface fracturing over parts of the mine.

"Remarkably, only one of the four reports provided so far, that of hydrologist Dr Mackie, recognises that the now confirmed seam to surface connected fracturing impacts are consistent with the predictions of the Tammetta equation," he said, referring to a formula by hydrologist Paul Tammetta.

​"The Tammetta equation is currently the only scientifically credible means of estimating the height of the drainage zone - the height of mine-void to surface connected fracturing," he said.

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