The New South Wales Government must immediately halt operations at Peabody Energy's Metropolitan Coal Mine in the Royal National Park near Helensburgh, following a new report which has uncovered the discharge of contaminated metals into Worona Reservoir which supplies drinking water to Sydney and the Illawarra.
Expert analysis by former WaterNSW hydrologist Peter Dupen has found that the rock beneath the Reservoir is cracking in unrecognised and unpredictable ways which is drying out catchments, diverting underground streams and spewing iron, manganese and other contaminants into the water supply.
Mr Dupen says coal extraction is causing large scale fractures to develop beneath ridges and valleys around the Reservoir.
"What we are now seeing is unexpectedly extensive fractures opening beneath the streams, stored waters and pristine catchments of the Woronora Special Area. This has led to several hundred meters of a perennial stream called the Eastern Tributary going dry since early 2017, as well as drainage of the neighbouring ridge groundwater which feeds the stream.
"If we continue to allow longwalls of coal to be extracted from the Metropolitan Mine, we will continue to see potentially catastrophic drying of the protected catchments and streams currently collecting Sydney's high quality drinking water. It's not that the water is leaving the catchment, it's that the pathways it is now taking to reach the reservoir is different to the natural filtering pathways and is much worse from a water quality perspective.
"Groundwater in the ridges is now draining out more quickly into the local streams. When the water emerges, it is saturated with iron, magnesia, aluminium and a range of other metals and salts," said Dupen.
The analysis of publicly available information was commissioned by the Nature Conservation Council with the support of the Sutherland Shire Environment Centre.
"This mine has long plagued the Royal National Park with sludge and damaged precious ecosystems, " said NCC Chief Executive Jacqui Mumford.
"Now it looks like the mine is also drying surrounding creeks and pumping even more pollutants into the water supply. Not only is our drinking water being threatened, but so is the health of one of Sydney's last koala habitats."
The subsidence effect is also causing upland swamps, streamlines and pristine forests - which naturally filter and cleanse the weather supply - to further dry out.
"I recommend that further mining beneath the Reservoir be immediately halted until the implications of this new type of impact are reviewed. If confirmed, the NSW Government should withdraw approval and leave this environmentally costly coal in the ground," said Dupen.
The NCC says mining under drinking water catchments must stop and is demanding that the NSW Environment Minister must immediately:
- Halt extraction and fully investigate the hydrological and ecological impacts of the Metropolitan Mine on the Woronora catchment, including its tributaries
- Rule out any expansion of mining under any water catchment
- Survey koalas in the Woronora Special Area to gain a full understanding of, and protect, this vital population
LINK to report: Metropolitan Coal Mine - independent review of environmental performance to 2022
Background
Metropolitan Coal Mine is owned by Peabody Energy. It is a continuation of a mine commenced 125 years ago, and the current "300-Series" of longwalls extending under the Woronora Special Area catchments was approved in 2009. Until 2018, these longwalls extracted coal beneath two major tributaries of the Woronora Reservoir, Waratah Rivulet and Eastern Tributary. Now the longwalls are being extracted directly from under Woronora Reservoir.
In 2000, parts of Waratah Rivulet were crushed by mine subsidence effects and sections of the stream became dry as longwalls were extracted progressively beneath them. To reduce further impacts, Peabody changed the design of the longwalls and Peabody's geotechnical engineers proposed to avoid such impacts in the future using narrower longwalls developed in a different direction.
In 2016 and early 2017, however, a kilometre long stretch of the other major undermined stream, known as the Eastern Tributary, unexpectedly went dry due to undermining. The water was found to be diverting into the rocky base of the stream and re-emerging not far above the Reservoir full supply level, now saturated with iron and other metals.
In 2018 the company began mining the "300-series" longwalls further north, directly beneath the stored waters of the Woronora Reservoir (see figure below).
Basal shear planes are flat, sub-horizontal movement planes at or just below the level of the valley axis, caused by contrasting stresses imposed by mining-induced subsidence of the ground surface. They were originally hypothesised by Ken Mills, Principal Geotechnical Engineer and Director from geotechnical consultancy SCT Operations P/L in 2007, and were confirmed at the nearby Dendrobium Mine in 2015. Whilst the development of these shear planes is no longer a surprise, we have never before understood that they could be extensive enough to divert streams or drain ridges over hundreds of meters. Based on the impacts detected by piezometers, which measure groundwater levels, at Dendrobium and Metropolitan Mines, the width of these shear planes can now be inferred to be at least 200 m, centred along the valley axis where the streams lie.
In the past, assessment has focused on the risk of draining stored waters through connective cracking into the underground mines several hundred meters below, which is what we have now confirmed is happening at the Dendrobium Mine. The impacts described in the current analysis of Metropolitan Mine are different however and were not predicted in the planning application nor subsequent analysis by Peabody.
Based on the evidence presented in Mr Dupen's review report, it now appears that the catchments are going to be much drier and the water quality in the Metropolitan Reservoir will become progressively worse.
