The initial hole or pilot bore has been drilled.

It's the first stage of pipeline construction across the Shoalhaven River.

The hole is 300 millimetres in diameter wide and has been drilled 1.4 kilometres underneath the river.

"This is a magic moment for us, it's a significant milestone in not only the REMs 1B project but for the local community as well," Shoalhaven Water asset planning and development section manager Robert Horner said

"The successful completion of this project will enable us to transfer reclaimed water from the Bomaderry new treatment plant to farmers on the Terara flood plain so there's a win-win for everyone here.

"We're just trying to maximise the beneficial reuse of the reclaimed water rather than put it into the Shoalhaven river and the ocean like it has been done in the past."

The next stage of the process involves doubling the size of the hole to allow piping to be put through.

"We are expecting the ream to take another 30 working days and then another 10 days after that before the pipes are put in and pressure tests are done," Project manager Jordan Moeser said.

There have been challenges in completing the pilot bore, particularly around the toughness of the rock.

"For us, the biggest challenge so far has been ground conditions, we were expecting sandstone we are reaching meta-sandstone," he said.

"It's strong and very abrasive so it's destroying the tooling.

"We allowed to go through with one bit of tooling but we've gone through six."

Operations Manager at UEA Jonathan De Vos said there are a few firsts for the project including the piping used.

"The material it's made from and the pressure it's rated to is certainly the first that's ever been used in Australia," he said.

"We've done a number of bores around this length but this one here is about 10 metres longer than one we've ever completed."

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REMS has been the biggest public works ever conducted by the Shoalhaven City Council. As well as the construction of the pipeline the project also involves upgrades to the Nowra and Bomaderry water waste treatment plants.

The project has not been without controversy though, with the Construction, Forestry, Mining and Energy Union (CFMEU) last year speaking out about the safety conditions on other sites overseen by contractor UGL.

Some of the concerns raised by the union included electrical issues, unclean amenities, unsafe access and exits, trip hazards and a lack of adequate fire extinguishers.

Robert Horner said the safety matters on the other sites were resolved 12 months ago.

"Yes, there was some union involvement on site, that was well managed by the contractor and all issues were resolved," Mr Horner said.

"Council has a number of its own safety inspectors and safety is always a number one priority on the sites.

"I'm not aware of any new issues from unions or SafeWork NSW."