Where environmental certainty keeps construction moving
The Sydney Metro West – Western Tunnelling Package is one of Transport for New South Wales’ major transport infrastructure programs, spanning from Sydney Olympic Park to Westmead, including the Clyde Stabling and Maintenance Facility and the Rosehill Services Facility.
For the Gamuda Australia and Laing O’Rourke Consortium (GLC), progress depends on more than excavation and logistics. Each worksite must meet Conditions of Approval and specific deed requirements, with investigation, remedial planning, remediation and validation executed and documented to a standard that withstands independent audit.
Across up to 10 construction sites, historical land use presented varied contaminant profiles and uncertainty at the interface between early works and main works. Teams needed a delivery model that could move seamlessly across locations, keep findings consistent, support fast field decisions and produce Site Auditor-ready documentation without slowing construction.
Building a repeatable model across multiple sites
Onterris provided strategic advisory and technical deliverables during the tendering process, tailored to tender requirements and stakeholder expectations. Key outputs included contamination risk reviews and three-dimensional contaminant models, which informed how bid teams described management measures and constraints.
During the project phase, Onterris embedded specialists within GLC teams to plan and deliver a consistent investigation and validation pathway along the corridor. Field programs included drilling and test pitting to collect soil, soil vapour and groundwater data. Remediation activities included capping, excavation and disposal, and monitored natural attenuation.
The work addressed a wide range of contaminants and an Acid sulfate soil assessment and construction advice supported decisions on reuse pathways for impacted materials. Where appropriate, environmental and human health risk assessments were completed and reviewed and approved by the Site Auditor.
From the outset, the focus remained practical. Investigation outputs fed directly into remedial planning aligned with construction sequencing, access constraints and safety controls. Validation boundaries and hold points were defined so site teams could manage risks during excavation, handling and stockpiling while maintaining project momentum.
In parallel, Onterris supported key package interfaces including groundwater monitoring, wastewater discharge impact assessment, wastewater treatment contractor selection, and inputs to the Construction Environmental Management Plan (CEMP).
Strong collaboration between the field team, the delivery team and the auditor is what keeps momentum. Shared understanding helps us resolve issues quickly and keep works progressing safely.
Delivering audit-ready outcomes with human outcomes in mind
The Sydney Metro West – Western Tunnelling Package demonstrates that disciplined investigation, remediation and Site Auditor-aligned validation put people first by keeping workers and nearby communities out of exposure pathways while confirming each site is suitable for its intended use.
That intent translated into documented, independently reviewable outcomes. Onterris delivered remediation and validation across more than 80 Areas of Environmental Concern, including friable asbestos and other legacy contaminants, confirming suitability for the proposed land use. To close the loop, the team produced 12 Remediation Validation Reports (RVRs) and Long-Term Environmental Management Plans (LTEMPs), each supported by Section A Site Audit Statements endorsing stages of delivery. Internal Certified Environmental Practitioners (Site Contamination) reviewed deliverables before submission to Sydney Metro and the Site Auditor, reinforcing consistency and traceability.
By applying specific Resource Recovery Orders, the program enabled the beneficial reuse of 1.3 million tonnes of tunnel spoil and more than 200,000 tonnes of treated acid sulfate soils, contributing to a cumulative beneficial reuse rate of 100%. Beyond material efficiency, this approach reduced reliance on off-site disposal and minimised waste movements that can intensify disruption around active construction precincts.
Where the project stands now
Work on the Western Tunnelling Package is coming to a close, with the audited documentation set providing a repeatable template for progressing complex sites under tight approvals requirements. The program has established an approach that other major infrastructure packages can apply: embed early, investigate with construction interfaces in mind, validate to an auditor-ready standard and pair remediation outcomes with practical resource recovery pathways.
