Diverted groundwater near mines may cause trees to die
Report has implications for proposed Shenhua coal mine after researchers found changing water table levels can affect the ecosystem several kilometres beyond mine boundaries. A new study has found open-cut mines that modify groundwater levels can affect trees and ecosystems several kilometres away from mine sites.
The study has implications for the $1.2bn Shenhua Watermark coalmine and the federal government’s proposed “green lawfare” legislation which aims to limit the power of people to challenge projects unless they are directly effected.
Sebastian Pfautsch, from the Western Sydney University’s Hawkesbury Institute for the Environment, was funded to examine eucalypts in Western Australia’s Pilbara region through a government-industry partnership with Rio Tinto Iron Ore.
The sites he studied were located around the Hope Downs mine (jointly owned by Rio Tinto and Gina Rinehart), and additional studies were carried out around a mine site near Tom Price and water bore fields that supply Port Hedland and Karratha.
The study, published in the international journal Ecohydrology, assessed the health of trees by measuring their water use at around mine sites where groundwater levels had artificially been lowered and raised or diverted to prevent the flooding of pits.
“We know Australian trees, such as eucalypts, can extend roots 30m or deeper into the ground to find water,” Pfautsch said.
Pfautsch found the water use of trees some several kilometres away from mine sites was sensitive to changes in groundwater levels.
“Where the water table had fallen to 19 metres below the surface, water use of trees was much lower compared to trees where the water table remained unchanged at around six metres below ground level,” he said.
“The tight connection between water use and the growth of trees implies that a reduction in water use will lead to a reduction in growth. In extreme cases trees can die of thirst.”
Pfautsch’s study suggests the implications of changing groundwater levels owing to mining can potentially extend beyond the boundaries of mines. Farmers on the Liverpool plains draw down on the groundwater to grow their crops.
It also has implications for the federal governments “green lawfare” amendments to the Environmental Protection and Biodiversity Conservation Act, now before a Senate committee.
If the legislation goes ahead, landholders and others not directly on resource project boundaries would have to prove they were directly affected.
Watermark’s environmental impact assessment statement states a total of 4,084 hectares of vegetation will be cleared over the 30-year life of the mine, including 738 hectares of box-gum woodland, listed as a “critically endangered ecological community” under the Environmental Protection and Biodiversity Conservation Act. The Breeza state forest is on the boundary of the mine.
Shenhua has pledged a “biodiversity offset program” to mitigate the impact of the mine, through rehabilitation work around Mount Watermark, the mine site and at a site in Barraba, 150km away. It also includes river red gums along the Mooki river, outside the south-east boundary of the mine.
The biodiversity management plan and biodiversity offset strategy must be prepared in consultation with the New South Wales Office of Environment and Heritage and the Department of Planning and Environment and approved by the secretary.
According to Shenhua’s environmental impact statement, within 10km of the project boundary, 35 bores are predicted to experience “maximum groundwater level reductions of greater than or equal to 0.1m (10cm)”.
“Of these four bores adjacent to the southern mining area have a maximum predicted drawdown of one to two metres,” the statement said.
It also said the groundwater levels are “largely predicted to recover rapidly within approximately five years as the pits are backfilled”.
Pfautsch said while hydrological modelling had identified the extent of declining water tables around the Shenhua Watermark mine, “the impact this decline may have on trees and ecosystems further away from the mine is unknown”.
“I am not a miner and I am not an environmentalist wanting to shut down mines, I am an independent scientist and I believe the knowledge from this study can be applied elsewhere,” Pfautsch said.
“Nobody should think you can dig a very deep hole without having any affect on the environment but when you have money and will available to reduce the impact, it can be done.”
In his reading of the public documents available on the Shenhua mine to the NSW government planning authorities, he said, the “fingerprint” monitoring work had not been carried out and the proposed monitoring program remained to be defined.
“For example, the environmental impact statement for the planned Shenhua Watermark coalmine concludes that because groundwater naturally occurs 20 metres below the surface where plants supposedly cannot reach it, the existing vegetation communities within the project boundary are not depending on groundwater,” he says.
“Hence, it is believed lowering the groundwater table will have no effect on these vegetation communities. But the source of water accessed by the existing vegetation seems to have never been determined, and trees often rely on capillary water in soil that rises up from the water table.”
He found that “intelligent reuse of abstracted groundwater” could help to reduce the wider ecological impact of mining.
“Sound water management, based on ongoing collection of data increases the chance that trees and forests remain healthy,” Pfautsch said. “The management of ecological water requirements of trees is essential and has been well executed in semi-arid landscapes like we studied in the Pilbara, but should also be implemented in other mining regions in Australia.”
A spokesman for the NSW planning department said state government had strengthened penalties for environmental breaches, with fines of up to $15,000 for a single breach, the most severe penalties in Australia.
“Assessments undertaken by the NSW Department of Planning and Environment take into account a range of environmental impacts both inside and outside the proposed project boundary,” the spokesman said.
“Once approved, conditions of approvals generally include the requirement to undertake monitoring of noise, dust, and groundwater, for example, at nominated onsite and offsite locations.”
Original article appeared on The Guardian, 8 September 2015 (Link)