Kerri Tonkin, a 47-year-old grandmother from South Australia, said she had her hat and glasses ripped off by a policeman during a protest on Monday. The officer then sprayed capsicum spray into her eyes, mouth and face from just one inch away.

"I've got a lot of damage to my eye," Ms Tonkin told Fairfax Media. She also said she received scratches to her face and had her arm and shoulder wrenched by the policeman who later told her she was lucky not be Tasered.

"I don't think pepper spray was necessary," Ms Tonkin said, adding that at the time she was chained to machinery with another woman and unable to move. "It was a totally peaceful project - there was no verbal, we didn't even swear."

She was taken to the Narrabri police station about half an hour away and treated by an ambulance officer.

Ms Tonkin was also charged with trespassing and resisting arrest as was Cyd Fenwick, a 46-year-old woman she was chained to at the time of the spraying.

Police media confirmed officers from the Barwon local area command used OC - Oleoresin capsicum - spray after two women "allegedly refused to comply with police directions".

Police did not detail why the pepper spray was used and when was the last time it had been deployed in NSW at an environmental protest.

Santos declined to comment on police operations.

"While Santos respects the right of people to partake in safe, peaceful and lawful protests, these protesters continue to break the law by illegally accessing a securely fenced construction site," Peter Mitchley​, general manager of Energy for Santos, said. "The safety of our staff, contractors and the community is our upmost priority."

'Extremely rare'

Naomi Hodgson, a spokeswoman at The Wilderness Society who was with the two women shortly before the incident, said it was "extremely rare" for police to resort to capsicum spray at environmental protests.

"It's a massive escalation," Ms Hodgson said. "I wouldn't be surprised if the out-of-hand action by police will galvanise the community even more."

The protest is focused on Santos' Leewood water treatment works that will remove salts from the waste water produced by the nearby CSG field planned by the company.

Opponents of the project say the desalination plant should not be proceeding without an environment impact statement. The plan for drilling 850 CSG wells posed "a great inherent risk" to the region's water aquifers that also are a major recharge source for the Great Artesian Basin, she said.

The arrests on Monday brought to 16 the number of people arrested and charged at the Leewood site protests over the past two months, which have drawn more than 100 people on some days, Ms Hodgson said.

The incident coincided with the first day for new Santos chief executive Kevin Gallagher.

About 10 protesters delivered petitions and letters signed by some 360 local landowners to the Sydney offices on Santos on Monday.

The women were issued conditional bail to appear before the Narrabri Local Court on February 23, police said.