Blue Mountains commuters had a frustrating week after a boulder was discovered above the train line at Glenbrook

Train services resumed between Penrith and Springwood on Saturday after a 20-tonne boulder was removed above the train line at Glenbrook and the area stabilised.

It follows a full week of delays for commuters while the work was carried out. The boulder had broken away from the cliff face and was at risk of falling on the train line below.

We have an obligation to not only ensure the line is safe, but that appropriate measures are taken to preserve the rock art and document the findings.

Howard Collins

Sydney Trains and NSW TrainLink Chief Executive Howard Collins  on Saturday said the line was back in service ahead of schedule thanks to the hard work of engineers and specialists to safely remove the boulder.

"We want to thank customers for their patience over the past week and commend our workers on site for their efforts," Mr Collins said.

"There is still some work to do at the site given the discovery of culturally significant Aboriginal rock art, but this will not affect the normal running of the Blue Mountains Line."

He said Sydney Trains would continue to collaborate with the Office of Environment and Heritage, local Aboriginal groups, and contractors on site to preserve the rock art.

"We have an obligation to not only ensure the line is safe, but that appropriate measures are taken to preserve the rock art and document the findings," Mr Collins said.

The Aboriginal hand stencils were discovered while work was underway to remove the boulder.

An independent archaeologist, specialising in Aboriginal heritage, had confirmed the multiple handprints as culturally significant rock art.

Aunty Sharyn Halls is the secretary of the Gundungurra Aboriginal Heritage Association which has an ILUA (Indigenous Land Use Agreement) over the site.

She was keen to access the site to see the hand stencils but said access could be an issue due to the steep terrain.

"I've been told they had to find an archaeologist that could abseil in there to confirm it [the find]," she said.

Axes had also been found on the site, she believed, making it as significant as nearby Red Hands Cave and a likely ceremonial site where Aboriginal groups travelled through.

"It's going to be pretty significant."

But she was worried about its preservation.

"We're going to have every man and his dog going to look at it. We will need a management plan."

She said the Office of Environment and Heritage had been in touch with her.

Sydney Trains said given the sensitivities of the discovery, they were currently unable to release any image or footage of the artwork.

"We acknowledge the traditional custodians of the land and we always seek to respect, recognise and celebrate Aboriginal culture across our network and organisation," Mr Collins said.

Removing the boulder in difficult terrain was a very involved process. Specialist crews abseiled down the cliff face to secure the boulder with heavy duty chain mesh to avoid any further instability during work. Then it was carefully broken up piece by piece. Broader stabilisation work in the area to protect railway infrastructure was also undertaken.

"The rock detachment was likely caused by a large tree root growing into the cliff and forcing the boulder out over time, according to our geotechnical experts," a Sydney Trains spokesperson said.

For a full week buses replaced trains between Springwood and Penrith, with several companies engaged from out of the area as well as local operators Compass Tours and Near or Far Bus and Coach.

"All local Blue Mountains bus operators on our emergency bussing panel were notified of the disruption at the same time and invited to offer their services," a Transport for NSW spokeswoman said.

"Due to the number of buses required to supplement services on the Blue Mountains Line this week, we have also sourced buses from surrounding areas, such as Lithgow and St Marys, to provide adequate resourcing and ensure safety comes first for our customers and drivers."

Many commuters weren't happy about the delays, taking to the Gazette's Facebook page to express their frustration.

"They should have to reimburse people who have to get cabs etc, especially late at night and there is no way to get home," wrote Nicole Marshall.

"It's very frustrating as the commute from the Upper Blue Mountains to the city is long enough," wrote Julie Roughley.

And parents were concerned for their children.

"My kids were catching a bus to replace the trains but the bus left early both going and coming home. That's not cool!" Nel Brooker said.

It also made for busier roads, as Stacey Mandee noted. "I work in Penrith and drive from the Lower Mtns. Traffic is crazy and as some are finding out there is no station parking at Emu Plains or Penrith after 7-7.30am. The traffic driving through Emu Plains is horrendous in the mornings."