LONGWALL MINING AND GROUNDWATER
Ms CATE FAEHRMANN
[1.07 a.m.]: I share my grave concerns regarding the unexplained drying up of Thirlmere Lakes, south-west of Sydney. Thirlmere Lakes are part of the Greater Blue Mountains World Heritage Area and are also on the Register of the National Estate. Longwall mining has occurred adjacent to the historic Thirlmere Lakes and I am worried that such mining may have contributed to the dramatic drying up the lakes experienced recently. It is believed that the lakes are fed by surface run-off and underground aquifers, yet have failed to fill despite the drought being declared over in the region since 2008 and recent rainfalls filling nearby bodies of water. Clearly, damage to such a precious natural asset is an issue worthy of attention by this Parliament. Longwall coalmining has taken place in recent years within 955 metres of Lake Werriberri, the largest lake in the group, and 700 metres of Lake Couridjah. This could be a contributing factor to the loss of water from the lakes.
The mining operation in question is Tahmoor colliery owned by Xstrata Coal. Longwall mining is an underground coalmining technique that involves removing a portion of an underground coal seam. Longwall mining can cause the land above the mined out coal seam to destabilise and collapse. This is known as subsidence. The extent of subsidence is influenced by various factors, including the width and depth of the longwall mine, topography, the type of overlying rock layers, the design of the mine and the location of the mine. These factors vary from site to site, so the amount of subsidence and its subsequent impacts also varies. Subsidence can cause river beds to crack and creeks to dry up.
Rivers SOS, an alliance of over 40 environmental and community groups, is calling on the New South Wales Government to mandate a safety zone of at least one kilometre around all rivers in the State. This is to protect aquifers, creeks and rivers from permanent damage by mining under or too close to them. Rivers SOS has been documenting the devastation of longwall mining activities on nearby watercourses. One example is the Lower Cataract Creek, which flows into the Nepean River at Douglas Park near Campbelltown. The following information is on the Rivers SOS website:
Ten longwall mines went underneath this stretch in the 1990s, at a depth of 430m beneath the river bed. As a result the rocky bed was badly cracked in hundreds of places. The water was polluted by ingress of saline and acidic groundwater and by ecotoxic chemicals leaching from fractured Hawkesbury sandstone. A massive fish kill was reported by a fisheries inspector. 50 per cent of the river's flow was lost down the cracks. Methane gas vents erupted along the river, which at one point measured at 20 litres per second—ten years later some vents are still active.
The river turned red in 1995-6, due to iron oxide reaction; ten years later it is a milky green colour except when flow is augmented by heavy rainfall. There are few fish, and algal blooms flourish while bacterial mats coat the rocky surfaces under water.
Photographs on the website show heartbreaking images of children swimming in areas in the 1970s that are now grossly polluted. The community has lost a much-loved river due to longwall mining. I strongly urge all members to visit the website and also to watch the organisation's 30-minute Rivers of Shame
At Thirlmere Lakes, the mining company Xstrata and the Department of Environment, Climate Change and Water have denied any association between longwall coalmining and the loss of water there. How this can be denied so unequivocally when the mining companies admit to their activities causing subsidence is beyond me. The Greens have joined Michael Banasik, the Mayor of Wollondilly Shire Council, and the Coalition in calling for an independent investigation to determine the cause or causes of the water loss. It is true that historically the lakes have dried out a couple of times during extreme periods of drought. However, the locals say that the lakes would always fill quickly after rain. In fact, other water bodies in the area and now full as a result of recent heavy rains. Much of the beds of Thirlmere Lakes are now bone dry, with a muddy peat bog in their centre.
I have visited Thirlmere Lakes twice in recent weeks and met with members of the local community and council representatives. It is a depressing sight, particularly given that Thirlmere Lakes has been World Heritage listed because of its unique natural assets. New signs have been posted warning visitors of the dangers of the mud. It is time we found out what is causing this and who, if anyone, is responsible, so we can ensure that other water bodies do not meet the same fate. I support the local community and its efforts for an independent investigation into why the lakes are drying up. The State Government must agree to an investigation as soon as possible so it can be determined whether any nearby mining activity has caused the loss of this water. But we need more than an after-the-fact investigation. Tough regulation of longwall mining is urgently needed. Surely our rivers, lakes and aquifers are too precious to turn a blind eye to their destruction.