Loading "We should be walking through 'squelch' now," said Duncan Rayner, a principal engineer at the University of NSW's Water Research Laboratory. "When this swamp was not impacted, you would have had water at the surface." Swamps in the catchment serve as a giant sponge, absorbing rain during falls and releasing water during dry times. As the endangered ecological communities dry out they allow greater erosion and can increase the fire risk, Mr Rayner said. Wongawilli Creek tributary 21 revealed deep cracks in the dry stream bed. WaterNSW believes the cracks were worsened by subsidence resulting from coal extraction about 400 metres below.

Julie Sheppard (right), a member of the National Parks Association, explains to other conservationists where the mine impacts are showing up at the surface. Credit:Nick Moir Loading "These are the most aggressive longwalls in any of the catchments," said Peter Turner, mining projects science officer with the National Parks Association. "The mining here's quite diabolical [and] more damaging than other mines." Dendrobium's longwalls reach as long as 2 kilometres, run more than 300 metres wide and as much as 4.5 metres high, he says. "Not allowing mining that could cause the drainage zone to reach the surface, with seam to surface connected fractures, should be a fundamental catchment protection principle and policy," Dr Turner said.

"The damage, degradation and water loss would be very much less than is so disturbingly obvious now.” Attention on the damage from mining in the catchment has increased along with the drought, as Sydney's catchments drop below 50 per cent full and residents get used to first-stage water restrictions. Cordeaux and Avon dams, the two main storages closed to the Dendrobium mine were at 41.5 and 48.3 per cent full as of Wednesday, according to WaterNSW. A spokesman for South32 said mineable reserves will be depleted by 2024, and that the miner had met all its performance measures. Its proposed extension would have a net economic benefit of $2.8 billion for the state, sustained about 400 jobs and ensure the supply of the metallurgical coal to customers at home and aboard until 2048.

"We take our environmental responsibilities seriously and understand the sensitivities of working within the Metropolitan Special Area, where the mine is located," he said. "The supporting [Environmental impact study] is informed by years of expert research into the environmental, social and economic aspects of the project and has been developed through extensive consultation with our stakeholders," the spokesman said. Duncan Rayner, a UNSW researcher, at a dried-up creek within the Metropolitan Special Area over the Dendrobium coal mine. Credit:Nick Moir Rob Stokes, the Planning and Public Spaces Minister, said: "Sydney’s drinking water is of paramount importance and we need to ensure its pristine condition is maintained." "Any application for mining in the catchment is subject to rigorous environmental assessment that includes input from Water NSW, the Dam Safety Committee and the Independent Expert Panel," Mr Stokes said.

For its part, WaterNSW said it was "preparing a submission on this project, which will be made publicly available in due course". However, in documents seen by the Herald, officials were much more definitive. Last October, for instance, Malcolm Hughes, manager of WaterNSW's catchment protection unit, wrote to the NSW Dams Safety Committee raising concerns about the impacts from Dendrobium's longwall 16. "We ... recommend that the Application be refused on the basis that the upper bounds of reservoir water loss estimates based on recent evidence suggests that the DSC-designated Tolerable Loss will be exceeded (1.6 million litres per day relative to Tolerable Loss limit of 1 ML/d) by the time that LW16 is mined," Mr Hughes wrote. Duncan Rayner, a UNSW researcher, at Swamp 14, a region now in relatively pristine condition but expected to be undermined and drained by future mining. Credit:Nick Moir A separate letter dated in February 2018 to David Kitto, a Planning executive, from Fiona Smith of WaterNSW's Catchment Protection unit, noted that the then Planning Assessment Commission had set conditions on extraction by the Wallarah 2 mine in the Central Coast region that should be applied to Dendrobium.

Loading The conditions included "No connective cracking between the surface, or the base of the alluvium, and the underground workings", the letter stated. "We believe that this condition provides an important precedent for protecting drinking water catchments overlying longwalls," Ms Smith wrote. "WaterNSW therefore suggests that a similar or higher level of protection should be afforded to Greater Sydney's water supply, and it would therefore be appropriate to require a similar condition in any future approvals of longwall mining in the Sydney drinking water catchment." An aerial image of a swamp in the Metropolitan Special Area. Underground coal mining is causing subsidence, triggering the loss of surface and groundwater, drying out some regions. Credit:Nick Moir Dr Turner of the NPA said it was “very telling and very troubling that Planning did not take up the recommendation from WaterNSW to, at the very least, provide the Dendrobium area with the catchment protections required by the PAC - now the Independent Planning Commission - for the Wallarah 2 coal project."