North West Treatment Hub, Sydney, Australia

Sydney Water is using the NEC4 Alliance Contract (ALC), in what is believed to be its first use in Australia, to deliver over AU$1.5 billion (£750 million) of wastewater treatment improvements across northwest Sydney. The programme introduces an affordability-led commercial model that ties all alliance members, including Sydney Water itself, into a shared pain/gain mechanism - a significant step forward in how major water infrastructure is procured and delivered in Australia. Sydney Water is using an NEC4 Alliance Contract (ALC) to deliver over AU$1.5 billion (£750 million) of wastewater treatment improvements in the northwest of the city. It is believed to be the first use of the NEC4 ALC in Australia.

A programme built for complexity 

The North West Treatment Hub Growth Program addresses wastewater capacity constraints across two key water resource recovery facilities (WRRFs) in Sydney's rapidly growing northwest. The first stage, worth AU$595 million (£300 million) and awarded in December 2023, expands treatment capacity at Rouse Hill WRRF and improves biosolids processing at both Rouse Hill and Riverstone WRRFs. A second stage worth AU$295 million (£150 million), awarded in December 2025, upgrades liquids capacity at Riverstone WRRF. Three further stages are planned over the next eight years as population growth in the region continues. 

Among the programme's most ambitious elements is the introduction of sludge carbonisation technology at Riverstone WRRF - set to be the world's largest and most advanced sewage sludge carbonisation plant. Wastewater sludge will be converted into high-quality biochar containing valuable phosphorus nutrients, while the process simultaneously breaks down PFAS 'forever chemicals', reducing public health risks. The North West Hub Alliance, formed in December 2023, brings together Sydney Water, John Holland, Stantec Australia and Kellogg Brown & Root to deliver the programme. 

An affordability-led model for alliance contracting 

The NEC4 Alliance Contract (ALC) was selected because it best aligned with the collaborative, integrated delivery approach Sydney Water needed to manage a multi-stage programme across complex brownfield sites. Rather than procuring each stage individually, the ALC creates a single framework within which the alliance designs and delivers solutions against a holistic affordability envelope - a budget established using reference-class-forecast benchmarking and risk-based cost estimates that includes Sydney Water's own costs, not just those of its delivery partners. 

Program Director Darren Wharton explains how the pain/gain mechanism underpins the model. 'The NEC4 ALC performance table links the pain/gain share for all alliance members, including Sydney Water, directly to the affordability envelope. Everyone's commercial outcome depends on the same thing: delivering the programme efficiently and collaboratively. That alignment is what makes it work.' Sydney Water is an experienced NEC4 user, having adopted the contract suite in 2019 for its 2020–2030 construction works and service frameworks, and is the first major infrastructure provider in Australia to use NEC as its standard procurement route. 

The NEC4 ALC performance table links the pain/gain share for all alliance members, including Sydney Water, directly to the affordability envelope. Everyone's commercial outcome depends on the same thing: delivering the programme efficiently and collaboratively

Darren Wharton, Program Director, Major Projects, Sydney Water

Benefits of using NEC 

• The NEC4 Alliance Contract provided the integrated delivery framework needed to manage a multi-stage, multi-site programme worth over AU$1.5 billion - believed to be the first use of the NEC4 ALC in Australia. 
• An affordability-led commercial model, enabled by the NEC4 ALC's performance table, aligns the pain/gain share of all alliance members, including Sydney Water, to a single holistic budget, incentivising programme-wide efficiency rather than project-by-project cost control. 
• The ALC structure supports delivery of technically complex, first-of-kind infrastructure, including what is set to be the world's largest sewage sludge carbonisation plant, within a commercially certain framework. 
• Sydney Water's established NEC4 procurement model, in place since 2019, provides the supply chain and client team with a consistent contracting culture across all programme stages, reducing friction and supporting long-term collaborative relationships.