Briefing - mining impacts and the Metropolitan catchments

The publicly-owned Woronora and Metropolitan Special areas extend from Campbelltown south to Robertson and cover more than 100,000 hectares. The Woronora catchment supplies water to southern Sydney, while the Metropolitan catchment meets the needs of the Macarthur and Illawarra regions. In total these Metropolitan catchments provide 20% of Sydney’s drinking water supply and all of Wollongong’s drinking water.

These catchments on the edge of the Illawarra Escarpment capture every possible storm event, and are our most reliable source of supply during drought times. The significance of these catchments will increase with climate change, as rainfall reliability will decline; so even a small reduction in catchment performance will be serious.

These pristine catchments are home to 40 threatened animals and 26 threatened plants, including the Spotted-tail Quoll and contain the largest koala population south of Sydney. They cradle significant rainforest and tall old growth forests, open treeless heaths, as well as nationally endangered upland swamps.

There are one hundred endangered upland swamps in the water supply catchments. They comprise the fountainheads of many streams in dry weather. These swamps are so often destroyed by longwall coal mining that scientists have described such mining as a 'key threatening process'.

These metropolitan catchments were recommended for World Heritage listing values in 1994 by the Royal Botanic Gardens as part of the Blue Mountains and surrounding plateaux. The continuity of wildlife habitats of this large area is unique on the NSW Coast. The only reason these precious catchments are not protected in nature reserves is the presence of extensive coal mining operations.

The table and map below reveal the extent of intensive coal mining in Sydney's water supply catchments. There is potential for for very serious environmental damage to these sensitive and precious water supply areas. There are six operational* and two currently proposed mines in the water supply catchments south of Sydney:

The full extent of damage from mining, however, is unknown. Monitoring of mining damage is incomplete and public access to the catchments is prohibited. Additional serious damage to our water supply catchments has been discovered by environment groups on three occasions: at the Elouera mine in 2000 (stream flow loss); and at the Dendrobium mine in January and February 2008 (additional major cliff falls and crevasses).

The Sydney Catchment Authority expect that 91 per cent of the water supply catchments will be mined, so there is significant potential for extensive and serious damage.

The intensive longwall mining method used by the collieries under the water supply catchment is causing damage. Longwall mining extracts long blocks (‘panels’) of a coal seam from deep underground. A panel may be three or four metres high, up to 350 metres wide, and several kilometres long! The typical longwall panel can take a year to mine. The longwall panels are located in parallel, separated by coal pillars.

When the coal panel is being mechanically cut, the strata above the advancing machine-cutter are propped up by very powerful roof supports, protecting the mine workers. But as the supports are moved forward with the advance of mining operation, the immensely heavy overlying rock collapses into the cavern created by the removal of the coal seam.

Fractured rock may extend to a height above the seam of 25 to 35 times the thickness of the mined coal panel. Above this level, the surface rocks settle and may crack – perhaps in a creek or under a swamp. Cracking and subsequent water loss can result in permanent changes to water catchments and groundwater aquifers.

In addition to cracking and falling groundwater levels, surface subsidence can cause hill slopes to collapse, escarpments to topple, increased erosion and eco-toxic stream pollution. In hilly country, the surface damage may occur as far as 1.5 kilometres from the mined area.

Several places in the water supply catchments south of Sydney have suffered serious damage due to longwall coal mining. At the Metropolitan Colliery, Peabody Energy has mined directly under the Waratah Rivulet that provides about 30% of water to Woronora Dam. The Rivulet has been badly cracked by longwall mining: much of its water is draining away; and Flat Rock Swamp, an important headwater source, has all but completely eroded away. For much of the Rivulet’s length, it only flows after heavy rain, and three attempts at remediation to restore flows have failed.

In the case of the BHP Elouera Mine, two creeks in the water supply catchment have been damaged. The longwalls are 185m wide at a depth of 340m, the damage to the creeks includes extensive and intense cracking of their rock beds and draining of all rock pools (small and large) in mined areas. Under normal unmined circumstances the affected streams would be flow during drought times (and this is the case with unmined creeks in the vicinity). Upland swamps above this mine have dried out, and then were scoured away in the following heavy storms.

There is a persuasive argument that water flow is being lost underground. In 2001 the Elouera Mine reported that water inflows had increased to 225megalitres a month (see graph of increasing water losses). In late 2007 and early 2008, there have been two events when the adjoining Dendrobium Mine suffered an inrush of water during heavy rain, including 50 megalitres of water flooding the mine over just four days. So there is a risk of water supplies draining into the mines.

Strong and effective protection measures are needed to protect our pristine catchments that are critical to Sydney and Wollongong and that will otherwise drain away and become polluted. The catchment is managed by the Sydney Catchment Authority, which was created in 1998 after the water contamination incidents. The Catchment Authority has a legislative duty to preserve the ecological integrity of the area, but does not have any power to prevent the impacts from coal mining.

The intensity of longwall coal mining has increased over the years. With underground longwall coal mining, the amount of surface movement and damage is greatly influenced by the width of the longwall mining panels and the depth of the mine. In recent longwall mining in the Metropolitan water supply catchments and nearby areas, widespread surface damages occur when wide panels of coal are extracted.

Each longwall needs to be given permission by the Department of Primary Industries, but the Department has a conflict of interest, as it is the primary advocate of mining in NSW. It has not imposed mining prohibition zones under the streams nor otherwise guaranteed the ecological sustainability of our essential water supply areas by reducing the intensity of mining. Rehabilitation techniques are rejected (eg. cement grouting of cracks) as these are experimental, have been only 50 per cent successful at best, and are polluting in themselves.

The issue of water loss and damage to the catchment was highlighted at the 2001 commission of inquiry into the proposed Dendrobium Mine. In its submission, Sydney Catchment Authority said, “ There is evidence of pools being drained, reduce flows and a reduction in water quality….a potential for cracking beneath swamps to drain a significant amount of water contained in the swamps. This could lead to drying of swamps – adversely affecting their ecological integrity but also reducing water flows downstream. Practical means of remediation are generally not available.” (30 July 2001). The three failed repair efforts on Waratah Rivulet since then demonstrates that nothing has changed since 2001.

Fact Sheet on Longwall Mining Damage
Colliery	Area Affected	Depth of Cover (m)	Panel width (m)	Pillar width (m)	Damage
Elouera 1993-2000	Wongawilli and Native Dog Creeks	340	185	40	Creek beds cracked, pools and creeks dry. Two swamps collapsed and eroded away.
Appin 1997-99	Cataract Tunnel	460	206.2	32.8	Shear stress fractures, cracks in wall and roof.
Appin 1999-	Cataract Tunnel	520	255.4	32.8	Greater shear stress fractures and cracks in wall and roof.
Tower 1988-92	Cataract River	430	110	40	Some damage.
Tower 1992-94	Cataract River	430	155	40	River bed extensively cracked, river dry, water pollution downstream.
Tower 1994-00	Cataract River	430	207	40	Greater bed cracking, river dry, more water pollution.
Westcliff	Georges River	400-500	250	35	River bed pollution, river dry, water pollution downstream.
Bulli 1980s	Cataract Reservoir	230	80	60	No damage.
Bulli 1990s	Cataract Reservoir	320	110	60	No damage.
Metropolitan 2006	Waratah Rivulet		158		Rivulet bed pollution, river dry, water pollution downstream. Flat Rock Swamp destroyed.
Dendrobium Area 1	Lake Cordeaux and streams	145-310	183	40	Soil slumps, rock toppling, cliff falls into stored waters, creek and rainforest damage.
Dendrobium Area 2	Lake Cordeaux and streams	105-360	225	35	Metre-wide crevasses, soil slumps, rock toppling, creek and rainforest damage.
Dendrobium Area 3	Wongawilli Creek and other streams	300-400	305	35	Predicted creek beds cracked, creeks and upland swamps drained, water pollution downstream.

Meanwhile, BHP-Billiton released expansion plans for the Dendrobium mine January 2008. The longwalls panels will be 300+ metres wide under twenty-two endangered swamps and several streams in our water supply catchments and plans to advance towards the actual stored waters.

In 2001 BHP-Billiton's experts predicted damage that included surface cracking up to 250 mm wide, drainage of streams, the draining upland swamps, mining induced landslides and rock falls affecting 10 per cent of cliffs, death of native vegetation due to methane gas emissions and water pollution from the emergence of ecotoxic groundwater. The BHP-Billiton's experts are very clear that maximising coal extraction will cause severe damage to essential water supply areas, a view more than confirmed by the metre-wide surface crevasses and water in-rush events into the mine; damage that is way excess of predictions.

The Dendrobium mining approval set a precedent for mining that is now fifty per cent more intense than operations prior to 2001. That level of environmental abuse is now being taken up by the other players. Even the lower intensity mining caused considerable damage to water catchments and supply infrastructure, as described in the above table. The Dendrobium Mine should not been approved and the proposed Stage 3 extensions should be refused due to the damage that will be caused.

Only the risk of catastrophe prompted a reduction of the approved Dendrobium mine layout by one longwall panel in the first area mined, and for the longwall panels in second mining area to be relocated away from Lake Cordeaux, but the intensity of mining was not reduced. The concern of the mine regulators was to prevent Lake Cordeaux being drained, not to ensure adequate catchment protection. A regulatory approach that seems to only draw a line when exploitation verges on madness.

Colliery	Catchment	Company	Mining Method
Appin* (CL 768,381,388 767)	Metropolitan	BHP-Billiton	Longwall
West Cliff* (CL 724)	O'Hares	BHP-Billiton	Longwall
Metropolitan* (CL 379, 703)	O'Hares and Woronora	Peabody Energy	Longwall
NRE No 1* (Bellambi West) (CL 745)	Metropolitan	NRE Gujarat	Longwall
Delta* (Elouera) (CL 768)	Metropolitan	NRE Gujarat	Longwall
Avon (CL 765)	Metropolitan	NRE Gujarat	?
Dendrobium* (CL 768)	Metropolitan	BHP-Billiton	Longwall
Bargo (CL 747)	Metropolitan	Xstrata Coal	Longwall
Key: CL= Coal Lease.

Catchment impacts of longwall coal mining