Metal mats were also used to allow trucks onto the site without becoming stuck due to the wet ground.

On Monday morning, the limbs and wet ground appeared to be the reasons for delaying the drilling.

But the government has stood by its assertion that it was a small group of protesters' fault that the works were delayed, despite a police officer at the scene saying the group were not causing obstructions.

The protesters remained at the entrance and allowed the machinery to enter the site. A Justice Department official told them they could not go past the gate while the works were being carried out.

Westbury Region Against the Prison committee member Peter Wileman said the arborist and drilling workers came and went several times in the morning before the branches were cleared and machinery entered the site.

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He said it was disappointing that there was no oversight from a conservationist or anyone from the Environment Department.

"We weren't chaining ourselves to the gate, we weren't in a position to stop anybody from going about their work," Mr Wileman said.

"There was nobody from conservation, no naturalist there to watch it. There was nobody there to tell them if they were standing on or driving over an endangered orchid."

When asked if the government maintained it was the protesters' fault that drilling did not commence on Monday, a government spokesperson said that position was maintained.

Attorney-General Elise Archer released a statement on Tuesday afternoon stating workers were "safely" able to begin works while ensuring "disturbance to vegetation and soil is kept to a minimum".

"These important geotechnical investigations will be fully cognisant of the local environment," the statement reads.