The new recharge pipeline in Perth is set to help further reduce the city’s reliance on climate dependent water sources as part of Water Corporation’s Groundwater Replenishment Scheme expansion. Qenos Alkadyne HCR193B, Australia’s first polyethylene PE100 with high stress crack resistance (HSCR), was specified by Water Corporation as the pipe material used with horizontal directional drilling (HDD) for this critical project to maximise asset lifetime.

To diversify Perth’s water supply in response to the impacts of climate change, Water Corporation is currently operating a Groundwater Replenishment Scheme that recharges drinking-quality recycled water back into the groundwater system. Water Corporation is currently expanding the scheme to double its capacity to treat and recharge up to a total of 28 gigalitres of water per year.

At the heart of the scheme is the Advanced Water Recycling Plant in Craigie, which further treats secondary treated wastewater to drinking water quality using ultrafiltration, reverse osmosis and ultraviolet processes. This water is currently recharged into Perth’s deep Leederville and Yarragadee aquifers via on-site recharge bores.

The scheme replenishes groundwater levels to be later abstracted throughout the region without any evaporative losses. The second stage of the scheme will see the duplication of the Advanced Water Recycling Plant, construction of four new recharge bores and four new monitoring bores across two offsite locations, and construction of the 13km recharge pipeline connecting the plant with the bores.

The pipeline will run mostly alongside the Yellagonga Regional Park but also crosses it at two locations. Given the environmental sensitivity of these crossings, pipeline installation by horizontal directional drilling (HDD) was selected for those sections.

Water Corporation Project Engineer, Wing Leung, explains, “As an alternative to open trenching through certain environmentally sensitive sections of the Regional Park, we chose to construct these sections via HDD of polyethylene pipe.”

Polyethylene’s flexibility combined with high integrity connections through butt welding make it the material of choice for HDD. Durability and integrity of the pipeline network is of utmost importance for Water Corporation, which is why they specified the latest generation PE100 HSCR — Qenos Alkadyne HCR193B — for the horizontally drilled sections of the pipeline. The material’s superior resistance to cracks induced by scratches and notches on the pipe potentially introduced during installation or through rock or root impingement during service life, is expected to prolong the asset’s lifetime.

The DN800mm pipe needs to withstand both internal and external forces, as well as high tensile forces during pullback through the 570m and 1300m long bores, which is why a high wall thickness of more than 90mm was selected. The inherent low slump properties of Alkadyne HCR193B enabled the trouble-free production of this challenging pipe dimension within tight tolerances at Perth-based manufacturer Enviropipes.

Piloting of the two bores proceeded well ahead of schedule, facilitated by the sandy ground conditions and experience of trenchless specialist contractor, Pipeline Drillers. The pipe segments of 12m each were joined together using two track-mounted welding machines achieving a throughput of six welds a day using single low pressure welding. The 570m section was pulled through in August and at the time of writing, the 1300m long section is scheduled for completion in October 2018. The remainder of the 13km pipeline will be completed using open trench and microtunnelling methods.

Alkadyne HCR193B features enhanced resistance to cracks while still having the capability to handle a wide range of dimensions. Water Corporation is in the process of requiring all polyethylene pipework used for potable water in its network to perform better than standard PE100. Part of this will include enhanced crack resistance performance characteristics, which Alkadyne HCR193B can provide.

Senior Engineer at Water Corporation, Angus Adams, comments, “This pipe material was specified to improve asset life and durability, which are key parameters when considering whole-of-life costs and maintaining supply to our customers.” 

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