Harpers Hill Reservoir and Lochinvar trunk main extension

Project summary

The Harpers Hill Reservoir forms part of the Maitland/North Rothbury water supply system in New South Wales, Australia. The volume of the existing Harpers Hill Reservoir provides limited capacity to the overall system, with a high drawdown and fill frequency. Pensar designed and constructed a new 7 ML potable water reservoir and pipework system, including the extension of Harpers Hill Lane, and constructed a 2.4 km trunk main. The upgrade enables Hunter Water to strengthen its water security, supporting regional growth for the next 15 to 20 years.

The background

Hunter Water is investing over AUD$30 million in its region’s future, and as part of this, anticipated the need to replace the ageing Harpers Hill Reservoir, along with constructing an additional pipeline to transfer a larger capacity of water to the reservoir in times of peak demand. As a trusted delivery partner of Hunter Water, Pensar was engaged to deliver the two separable portions of the project, including the design and construction of a 7 ML reservoir and the construction of a 2.4 km trunk main.

The Harpers Hill Reservoir and Lochinvar trunk main upgrade provides more efficient and resilient infrastructure, meeting the demands of the growing population, maximising the life of the asset without unnecessary costs and supporting Hunter Water’s commitment to proactive asset management for efficient and sustainable infrastructure.

The multidisciplinary approach/strategy

Within the delivery scope of the project, Pensar engaged the specialist services of fellow RSK Australia companies EDP and Extent Heritage.

EDP assisted Pensar with managing asbestos contamination, which was identified during project delivery. EDP undertook a detailed site assessment, which included stockpile characterisation and handling advice for multiple stockpiles on-site, and provided general management advice and on-site technical guidance. EDP’s advice supported Pensar with mitigating potential exposure risks for workers and future site occupants, reducing the volume of materials requiring off-site disposal and enabling the safe construction of the new reservoir to continue as planned.

Extent Heritage undertook heritage assessments on the multiple heritage findings on-site, liaised with authorities to obtain permits, directed excavations and provided closeout reporting for a heritage homestead complex found in the project’s bulk excavation zone. Extent Heritage’s management and guidance on the heritage components at the Harper’s Hill site ensured there were no significant project delays or impacts, enabling construction to continue on schedule.

As RSK Australia businesses, Pensar, EDP and Extent Heritage were able to leverage each other’s unique expertise, delivering more comprehensive solutions and maximising Hunter Water’s desired outcome of the asset enhancement to its water network.

The challenges

Effective management of multiple services within the road reserve during both the design and construction phases was crucial to maintaining workflow continuity and minimising programme disruptions. Additionally, proactively mitigating the impact of significant wet weather events during the civil works was essential in safeguarding project timelines and budgets.

Commencing in June 2024, the Harpers Hill Lane extension was initiated to provide all-weather access to the reservoir site. However, due to early subgrade challenges, a pause to works occurred for a redesign. This redesign impacted site access and egress between June 2024 and February 2025. During this time, clear and consistent communication with the local community, subcontractors and suppliers was critical to ensuring that all deliveries, vehicle movements and concrete pours were carried out safely and without delay to the overall project schedule.

The concrete structure phase of the reservoir project was delivered during the peak summer period, requiring close monitoring of both weather conditions and the health and safety of all site personnel. Managing heat stress risks and maintaining safe working conditions were key priorities throughout this stage.

The solutions

Dispensations from Hunter Water standards were sought and approved to optimise reservoir design elements, influenced by Pensar’s significant construction expertise, including inlet/outlet positioning, roof gradients and metalwork selection. Additionally, the trunk main was realigned to avoid live services while maintaining all design parameters and intended outcomes.

Site delivery notices were implemented for all subcontractors, suppliers and clients engaged in the reservoir project. These notices were also implemented to notify local communities throughout the project phase and were essential in ensuring that all site access was well coordinated and communicated.

To reduce the impacts of high temperatures, early morning concrete pours were approved and scheduled. While effective, these early hour operations required further coordination to ensure all subcontractors and suppliers were on-site at these specific times. Despite these challenges, the project team maintained consistent delivery and upheld the programme schedule through proactive planning.

The impact

Targeted planning and procurement enabled Pensar to accelerate the programme, with the 2.4 km trunk main completed six weeks ahead of the original 35-week schedule. Early stakeholder engagement and identification of acceleration opportunities in the design and construction of the reservoir have positioned the team to achieve completion four weeks ahead of the original 71-week programme.

The Harpers Hill Reservoir and Lochinvar Trunk Main Project enhances water security and supply reliability, supporting long-term sustainability and water security for Hunter Water and its customers. This critical infrastructure upgrade not only strengthens asset resilience but also contributes to improved community health, economic growth and overall quality of life for the region.