TORONTO (miningweekly.com) – Midtier copper miner Taseko Mines late on Monday published its critique of the Canadian Environmental Assessment Agency (CEAA) on its website, saying the CEAA did not intend to post online the company’s criticisms of the panel review for its proposed New Prosperity mine, in British Columbia.

The panel had earlier this month found that the company's revised plan for a copper/gold mine in British Columbia posed significant threats to the environment.

However, in a surprising twist to the permitting saga surrounding the proposed mine, lead consulting engineer Knight Piesold had earlier this month determined that it appeared that Natural Resources Canada (NRCan), and subsequently the federal review panel, had used the wrong design in their analysis of seepage rates from the tailings storage facility.

In an eight-page letter to the CEAA, Taseko outlined why it believed the panel made a mistake, saying the panel’s criticism of the project’s tailings storage was central to its negative findings.

Taseko also wrote to the federal Environment Minister Leona Aglukkaq, saying she was supplied with fundamentally inaccurate information to base her final decision on.

Vancouver-based Taseko on Tuesday said the CEAA had asked it to explain the company's position that the panel had erred in its finding on the technical aspects of New Prosperity's tailings seepage and water quality, to which it had duly responded.

“Publicly requesting information, and then choosing not to release the results of the request in a similar manner creates an inaccurate portrayal of Taseko and an impression in the minds of the public that our critique of the panel's findings are somehow flawed,” Taseko president and CEO Russell Hallbauer complained in a statement.

He added that for that reason Taseko had posted the specific documents on its website to ensure that shareholders, community stakeholders and the general public were fully aware of the facts.

Taseko said: "When a proponent brings forward valid scientific evidence using some of the most respected experts in the world, it is not incumbent upon the proponent to speculate as to the nature and source of error that may be made by other parties presenting different information. This is particularly true in circumstances where the error is so outrageous as to be nearly unfathomable."

The company added that the panel relied heavily on modelling undertaken by NRCan, which had indicated that there would be significant seepage from the tailings storage facility into Fish Lake. The panel's findings regarding the expected seepage, and the related impacts on Fish Lake, were integral to the panel's conclusion that the project was likely to cause significant adverse effects on fish and fish habitat, wetlands and aboriginal interest in the Fish Lake area.

The design proposed by Taseko for the tailings storage facility included a continuous low-permeability compact soil liner to restrict seepage losses. This was a common and acceptable practice for modern facilities that had been recently permitted and developed in British Columbia and elsewhere in the world, the company said.

The NRCan design, which was the basis of the federal review panel’s analysis, was completely different to the Taseko design, as NRCan had assumed that the low permeability basin liner was not included and that seepage would, therefore, readily leak into more pervious overburden and fractured bedrock.