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Porirua City Centre Wastewater Retention Tank
DIALOG Fitzroy was engaged by Downer Utilities NZ Ltd to deliver the mechanical scope for the Porirua City Centre Wastewater Retention Tank Project. The work formed part of a major infrastructure upgrade aimed at improving wastewater resilience and storage capacity within the Porirua city catchment.
Scope of Work
DIALOG Fitzroy was responsible for the full mechanical delivery of the project, including:
Project Management & Delivery
The scope covered overall project coordination and execution planning, management and documentation of QA/QC processes, and interface management with Downer and other contractors to ensure seamless communication and integration across all work fronts.
Engineering & Design
The engineering and design scope included the structural design of supports, preparation of detailed fabrication drawings, and development of material take‑offs along with comprehensive shop‑level detailing to support accurate and efficient fabrication.
Procurement & Fabrication
This scope involved the procurement of stainless‑steel materials and fittings, workshop fabrication of piping spools and structural supports, and all required inspection, testing, and statutory approvals prior to delivery to site.
Mechanical Installation
Mechanical installation works included the installation of stainless‑steel piping systems across the pump station water supply, storage tank inlet and outlet pipework, overflow and overflow dissipator systems, and manways with associated pipework. It also included installation of valves, a flowmeter, a penstock, mechanical equipment, as well as the pump duckfoot and pump assembly.
Testing & Quality Assurance
The testing and QA scope included shop‑based hydrotesting in accordance with ASME B31.3, 10% radiographic NDT testing, compliance with an ISO 9001:2015 accredited QA system, and provision of complete Manufacturing Data Records (MDRs).
Execution Strategy
Engineering & Design
The execution strategy commenced with early engineering and design development, which involved a detailed review of IFC drawings and mechanical specifications, development of fabrication drawings and shop isometrics, and the structural design and detailing of supports. This phase also included verification of material take‑offs, a comprehensive constructability review, and early identification of interface points with civil structures and embedded items.
Fabrication
The execution approach relied heavily on extensive off‑site fabrication, where piping spools and structural steel components were produced within controlled workshop environments. All welding activities were completed in accordance with qualified WPS procedures and supported by 10% radiographic NDT inspection to meet ASME B31.3 requirements. Shop‑based hydrotesting was undertaken to minimise the need for site‑based testing, and weld passivation was completed prior to delivery.
Site Installation
The installation works included placement of structural supports and embedded plates, followed by mechanical installation of stainless‑steel piping systems, valves, the penstock, flowmeter, pump duckfoot, and other associated equipment. Final bolt‑up of flanged connections was also completed as part of this phase. The approach ensured that most welding occurred off‑site, reducing hot‑works exposure and improving site safety.
Health, Safety and Quality Management
Health and safety formed an integral part of the execution strategy and were managed through a site‑specific Safety Management Plan supported by task‑based JSEAs and Work Method Statements. A comprehensive permit‑to‑work system, regular toolbox meetings, and controlled lifting plans for mechanical equipment were implemented, along with active management of interface risks between concurrent trades. Quality management was delivered through DIALOG Fitzroy’s ISO 9001:2015 accredited system, incorporating approved Inspection and Test Plans, full weld traceability, material certification reviews, NDT and hydrotest documentation, and the collation of all Manufacturing Data Records (MDRs) for final handover.
Commissioning Support & Handover
Commissioning support and close‑out activities included the completion of mechanical installation checks, attendance during commissioning as required, and timely rectification of punch‑list items. All MDRs and QA documentation were finalised and submitted to support the handover process, with practical completion achieved through formal sign‑off procedures.
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