Claims that Shenhua's restricted coal mining will avoid affecting the aquifers of the rich farmlands of the Liverpool Plains are "false and ignorant", former state and private agronomists have said in a letter to Premier Gladys Berejiklian.
The government last month paid the Chinese coal miner $262 million for just over half the exploration licence area of the proposed mine at Watermark in northern NSW. Energy Minister Don Harwin said the buyback would ensure there was no mining on the fertile black soils of the plains.
But the agronomists, five of whom worked for the Department of Primary Industries or precursor departments, said limiting the proposed open cut mine to ridges would still likely affect surface and groundwater flows in the plains and downstream regions.
"The claim that mining the ridges above Breeza will not have an impact on farming operations is false and ignorant," the letter's authors said.
"Hydrogeological investigations have shown that there is a high degree of connectivity between the alluvial aquifers throughout the Namoi Valley."
Brian Tomalin, a retired cattle farmer and a former Namoi Catchment Management board member, told Fairfax Media endangered ecological communities such as whitebox woodlands were also at risk from impacts of an open pit reaching as deep as 300 metres.
"There's more at stake than just the agriculture," Mr Tomalin said. "If you drain the alluvial aquifers you'll never get them back."
Mr Harwin said Shenhua "must meet a range of Commonwealth and NSW consent conditions". The company would also have to apply for a mining lease, which it hadn't done yet.
Phil Laird, a co-ordinator for Lock the Gate, said the government had missed an opportunity to knock the mine on the head.
"The Minister would be aware that a mining lease, once applied for, cannot be refused in NSW if it is for a mining project that already has state significant development consent, as Watermark does," he said.
"If the government had cancelled the Watermark exploration license when they had the power and opportunity to do so, Shenhua would not have been able to apply for a mining lease."
The retired agronomists said a range of studies indicated that, at the least, the government should be demanding more research to assess the risks posed by the mine.
"The Namoi Catchment Water Study, the Independent Expert Scientific Committee and the Federal Environment Minister all identified the need for more information to inform the decision-making process," the letter said. "To date this has not happened."