BHP Billiton was granted approval by the NSW government for what is believed to be the most aggressive coal mine ever attempted beneath the Special Areas at the core of Sydney's water catchment without an accompanying groundwater impact study.
The Dendrobium mine, located within the Metropolitan Special Areas west of Wollongong, won approval in February 2013 by the Department of Planning and Environment for five of 10 longwall extractions being proposed for Area 3B.
BHP did not submit a completed groundwater impact study until March 2014, some 13 months later, which gave it a tick of approval. WaterNSW, the catchment authority, said it did not receive that report until October 2014.
"The Area 3B longwalls are the widest currently being extracted in the Special Areas, with what appears to be the largest extraction height ever used in the Special Areas - and among the largest extraction heights used anywhere in NSW," said Dr Peter Turner speaking on behalf of the National Parks Association (NPA) of NSW. "Such aggressive mining risks significant consequences for surface and near surface waters".
"Approving the most aggressive longwall extractions ever used in Special Areas without a groundwater assessment is deeply disturbing," said Dr Turner. "The approval and the manner it which it occurred suggests disregard for the legislated purpose of the Special Areas - to protect Greater Sydney's drinking water."
Dr Turner has written to the Planning Minister Rob Stokes, Environment Minister Mark Speakman and senior government officials to raise concerns regarding the approval.
Mr Stokes said he has been advised that there is "no evidence that the company has breached any consent conditions relating to longwalls 9-13".
"Despite this, I have asked the Department and as appropriate, Water NSW and the Office of Environment & Heritage (OEH), to carry out an inspection of the recent mining activities," he said. "This report will be made public."
The above map shows the Dendrobium mine west of Wollongong, with the new longwalls at the top left of the red markings.
'Robust' assessment
"The department's approval of the mine's management plans follows robust and detailed assessment against the requirements of its consent," a spokesman for the Department of Planning said.
"In this instance, because of the sensitive nature of the proposal and its potential impacts, the department made the draft management plan publicly available and sought advice from other agencies, including OEH and the Sydney Catchment Authority (now Water NSW)."
However, the public and agencies, such as the OEH and the SCA were left largely in the dark about what BHP's groundwater consultants found in the lead up to the approval in 2013.
In October 2012, consultants Coffey Geotechnics prepared a groundwater impact assessment of the mine's impact, a copy of which remains on the Department of Planning's website.
Agencies and the public prepared submissions on that report with the Sydney Catchment Authority praising it as "sound and well-researched and provides an important step in the development of a rigorous regional groundwater model."
The work underpinning the assessment was subsequently published in the peer-reviewed Groundwater journal.
However, for reasons unknown, the assessment was for a mining height of just 3.4 metres, considerably less than the 4.6 metres BHP planned.
A revised report was provided to BHP in November 2012, which then rejected both reports. It then asked HydroSimulations, a much smaller consultancy, to conduct a fresh study.
Longwall mining involves the mechanical extraction of a slab-like volume of coal that's typically 150-400 metres wide, three to four metres high and up to several kilometres long. The extraction results in subsidence, the downward movement and collapse of the rock above into the void left behind.
The Area 3B longwall extractions are 305 metres wide and all but the first are up to 4.6 metres high.
The Dendrobium mine is already the wettest in the Special areas with rain-dependent inflows of as much as 13 million litres a day - more than five Olympic swimming pools.
'Farcical'
Adam Searle, the Opposition energy spokesman, said the Baird government should explain what it knows about the competing studies and "explain its failure to exercise proper oversight".
"Approving a mine without undertaking a proper groundwater study defies belief, especially in one of the Special Areas," Mr Searle said. "If the government's attitude towards Special Areas is as cavalier as this, it raises serious questions about its approval process for all mines. "
Greens mining spokesman Jeremy Buckingham said the approach was "farcical" and called for an independent external inquiry: "If they are approving mining under the water catchment without critical studies or with conflicting studies, then that is negligence with significant consequences."
"The Department of Planning's attitude is that their job is to facilitate coal mining regardless of other consequences," he said. This is reckless and stupid in an era where coal is dying and when the impacts of getting it wrong are so enormous."
The first three of the five approved longwalls pass beneath the four large and important swamps which contribute to the water supply for Sydney and Wollongong. Dr Turner noted that the state's Chief Scientist had identified Sydney as the only major city in the world with mining beneath its main drinking catchment.
Reports queried
The Planning Department refused to state when it informed the catchment authority or OEH that the report they made submissions on was no longer considered valid by the project's proponent.
It appears that Planning did not attempt to consult with the agencies or independent experts and assess whether there was a sound scientific basis for BHPs rejection of the 2012 groundwater assessments.
Planning has also declined to answer whether it sought comments from OEH or the SCA about the quality of the replacement study, which was provided in March 2014 by HydroSimulations.
A spokeswoman for WaterNSW said the agency was not aware that the October 2012 report had been rejected.
"What is [Planning's] their view of the work that was rejected?" Dr Turner asked. "I find it remarkable that they appear to have accepted BHP's rejection of the Coffey assessment without question."
Coffey, meanwhile, defended the quality of its work. "We stand by the integrity of our reports," a spokeswoman said.
The operator of the mine, Illawarra Coal, is now part of South32, a collection of assets spun off by BHP earlier this year.
A spokeswoman for South32 declined to provide Fairfax Media with a copy of the corrective report of November 2012. Planning denies it ever received that report but won't say whether it was briefed on the findings.
"Illawarra Coal's applications to mine are comprehensive in nature and include predictions of impacts based on years of scientific data collected by experts," the spokeswoman said. "Where changes to reports, which are part of the approval process, are made by independent experts to reflect improvements in the assessment methodology and/or modelling, they are (and were on this occasion) advised to government."
Fracture zones
Dr Turner said that applying the now peer-review and published equation used for Coffey's modelling demonstrates how significantly the height of the fracture zone that forms above an extraction is affected if the longwall is 3.4 metres or 4.6 metres deep. For 4.6-metre high extractions the fracture zone reaches the surface above the mining. The fracture zone allows water to drain relatively freely towards the mine.
In the charts below, the red dots show where the fracture zone reaches the surface, pink is for 25-50 metres below the surface, orange 50-100 metres and yellow more than 100 metres below. Here is the 3.4-metre longwall estimate:
The assessment provided by HydroSimulations finds a much lower fracture zone height (see chart below) for the mining. Dr Turner finds that the database behind this assessment has flaws and anomalies and has written to the Planning Minister raising these concerns.
The NPA is calling for an inquiry into the approval of the Area 3B mining and other actions by the Department of Planning. They are also calling for reform of the way mining assessments are carried out in NSW.
"The Area 3B approval demonstrates the problems of allowing mining companies to select, fund and reject consultants at will" said Dr Turner. "It also demonstrates the problem of mining companies being allowed to decide what material is made available to the government and what is not."
By contrast, most of the longwalls would get categorised as in the "red" zone at 4.6 metres:
The following chart, reproduced from a paper by P. Tammetta in the Groundwater journal, illustrates how underground mining leads to fracturing of the ground as subsidence fills the cavity, or goaf, left behind after extraction of the coal.
Both Planning and South32 said the mine extension was being monitored closely.
"The mine is subject to compliance checks and the department is satisfied that the performance measures in place are robust," the spokesman said. "The department will continue to monitor impacts on all upland swamps, watercourses and groundwater."
Three of the first five longwalls have been completed. According to South32, the average depth on Longwall no. 10 that has been completed was 3.9 metres.
Fairfax Media sought details of the maximum depth reached during extraction, a figure the miner had previously revealed for its longwalls but so far has not done for No. 10. That information is not available, the South32 spokeswoman said.
