Resources Regulator looking at Mount Arthur coalmine over excavations near a former coal washery tailings dam

The Newcastle Herald was contacted about the job on Saturday because of safety concerns.

The Herald was told that the crew working in the area for contractor Daracon did not know about an old tailings dam on higher ground above where they were working, which was capped, and so supposedly firm or solid ground.

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In an account disputed by BHP, the Herald was told that work had stopped at the site when mine tailing sludge sprayed from a cut made by the excavator, spurring fears that the hillside could be unstable.

Contacted for comment, the main investigative body for coalmining in the state, the NSW Resources Regulator said it was "aware of an incident that occurred at Mount Arthur and that "an investigation has commenced".

But a BHP spokesperson said later that the regulator had not formally begun an investigation and that it was only doing so because it was obliged to because of the questions put to it by the Herald.

According to BHP, the Resources Regulator had not been told because it was not held to be "a reportable event".

"Daracon contractors were completing cut back excavation for (a) western tails wall when the filtration zone of (an) old tailing dam was intercepted," BHP said, describing the work to start excavating for a new dam.

(Mine "tailings" are a liquid sludge that is the waste material from a coal washery.)

BHP said the liquid was not mine tailings but "a small amount of water" that "seeped to the surface" from a filtration zone".

It was only discovered when "the workers returned from their crib break and reported a small amount of water had pooled over an area about two metres by two metres, and asked for the area to be inspected".

"The area will be backfilled and the design modified to accommodate this unexpected result," BHP said.

The tailings facility was being built in accordance with "highly regulated management practices".

A Daracon spokesperson said on Sunday evening that the job was a BHP and the company was not authorised to comment.

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