Hard conditions, detailed approach: making connections in the Northern Beaches

Steep, rocky, and accessible only by water, many parts of the Northern Beaches are as secluded as they are beautiful. But with the Mona Vale area earmarked for a new NBN connection, a thoughtful and well-planned HDD approach was required to ensure Northern Beaches locals will be even better connected.
Too isolated for large populations, and with ground conditions too hard for farming, the Northern Beaches’ natural beauty has endured. With many locals living amongst the secluded beaches and national park areas, with modern times have come modern demands, including rollout of the NBN to the area via the Mona Vale Western Bay NBN Outfalls. Thus, the challenge was presented: how best to install this vital infrastructure in such an inaccessible, environmentally sensitive location, with rock conditions?

Strict environmental requirements

The project was bound from the start by rigorous environmental conditions. With much of the location covered by Ku-ring-gai Chase National Park, a trenchless solution was non-negotiable in order to minimise environmental impact. Central Coast-based HDD specialists Superior HDD were engaged by Downer to complete the 4 x HDD ocean outfall connections of the HDPE pipes.

Superior HDD Managing Director and Operations Manager, James Burch, recognised the project’s challenges immediately. “This is a very sensitive national park area, with many parts only accessible by water,” he said. “HDD was the only way to do it, and we knew with good planning, design, and risk mitigation, we would get it done right.”

Minimising risk

James explained that his priority was first to fully understand the project’s risks in detail. “We know the ground conditions in this area very well, and while the consistent Hawkesbury sandstone provides hard but predictable drilling conditions, being such a sensitive area, hydrofracture was not an option,” he said. “So we had our HDD design specialists complete a detailed profile and alignment and hydrofracture assessment, coming up with an ultraconservative, deep profile to minimise frac-out from that perspective,” he said.

From there, drilling fluid was the next step. “We needed bentonite to ensure optimal borehole performance and cuttings removal, but we couldn’t risk release of this fluid into the surrounding waters,” James said. “So we devised a detailed drilling fluid plan which used a bentonite program for most of the initial pilot, then a complete displacement of the hole, replacing all fluid with an environmentally low-impact xanthan gum mix,” he said. “This allowed us to punch out using the biodegradable xanthan gum fluid, as well as to responsibly plan, monitor, and analyse our returns for the entirety of the bores.”

Practical implications

Mobilising their Ditch Witch JT60 All Terrain midi rig and support equipment to the isolated sites also required many practical adaptations. “Many of the project areas are accessible only by water, and being ocean outfalls, much of our support equipment was transported and set up on barges for the duration of the project,” James said. Along with limited accessibility, the steep and rocky environment added additional challenges. “For more than one crossing, there was a 50m elevation difference between the drill site and the mud recycling system on the barge,” James said. “We rose to this challenge by supplying top of the range, powerful transfer pumps, as well as extensive auxiliary equipment to minimise possible interruptions.”

Community and National Parks engagement

James explained that the project required involvement of a range of stakeholders, and that Superior HDD seized the opportunity to demonstrate the strengths of HDD. “We had eyes on us for the whole project. In such a pristine environment, the local community was very environmentally conscious,” he said. “But we consulted closely and regularly with stakeholders to ensure we were fully across all environmental requirements, and to put concerned locals’ minds at ease. We also don’t rely on subcontractors for any of our HDD equipment, so we were able to personally consult with major stakeholders like National Parks, and then directly supply all gear in compliance with their strict requirements, including tracked machinery only.”

Successful Connections

The final of the four connections was completed in late September, on budget and within required timelines. “We were proud to showcase the accuracy and environmental benefits of HDD with this project, proving that with good preparation and risk mitigation, it’s a safe, responsible method in even the most pristine environments.”