Targeted Contamination Assessment for Substation Upgrade – Hunter Valley NSW
Prepared by Confluence Environmental — contaminated land and environmental compliance consultants supporting infrastructure, remediation and earthworks projects across NSW.
Confluence Environmental was engaged by a Tier 1 contractor to undertake a targeted contamination assessment in support of a substation upgrade and replacement of electrical infrastructure within the Hunter Valley, NSW.
The assessment was commissioned to address specific data gaps identified during a previous Preliminary Site Investigation (PSI) and to confirm whether contamination risks were present within areas proposed for bulk earthworks and excavation.
Project Background
The project site is located within the footprint of a former power generation facility, where historical operations were known to have resulted in the placement of slag and industrial fill materials across parts of the site.
While a prior PSI had established a general understanding of site conditions, further intrusive investigation was required to refine contamination risk within discrete areas directly affected by the proposed substation upgrade and associated access works.
Given the scale of earthworks and the sensitivity of electrical infrastructure upgrades, the client required a focused, risk-based investigation capable of confirming whether contamination constraints would impact construction activities.
Scope of Services
Confluence Environmental delivered a targeted investigation program specifically aligned with the proposed works, rather than a broad site-wide reassessment.
The scope of work included:
Review of existing PSI findings and identification of data gaps
Development of a targeted site investigation strategy
Intrusive investigation at locations proposed for excavation
Assessment of contamination risk associated with planned bulk earthworks
Reporting to support construction decision-making and regulatory confidence
Field Investigation Methodology
The investigation was undertaken using a combination of drilling and test pitting techniques to characterise subsurface conditions across the proposed works footprint.
Drilling works
Eight boreholes were advanced to depths of up to 6 metres below ground level using a solid flight auger mounted on a truck. Borehole locations were selected to intersect areas of deeper excavation associated with substation infrastructure.
Test pitting
An additional eight test pits were excavated using an excavator along a proposed access track to assess shallow fill conditions and confirm lateral variability in subsurface materials.
Soil samples were collected at representative depths and submitted for laboratory analysis targeting contaminants relevant to the site’s historical use.
Key Site Considerations
The primary contamination concern for the site related to the presence of slag material associated with former power station operations. Slag can present variable chemical characteristics depending on origin and placement history, requiring careful interpretation in the context of earthworks risk.
The investigation was designed to distinguish between widespread contamination and localised legacy material that could be managed through standard construction controls.
Investigation Outcomes
The targeted contamination assessment did not identify any gross contamination within the investigated areas that would preclude the proposed earthworks.
Minor, localised contaminant elevations consistent with historical slag placement were identified in limited locations. These materials were assessed as manageable within the context of the proposed works, subject to appropriate handling, segregation and material management measures.
To support lawful material handling during construction, Confluence Environmental also undertook waste classification of excavated materials likely to be generated during the works. Classification outcomes confirmed suitable management pathways for slag-affected soils and informed practical controls for bulk earthworks activities.
Overall, the findings confirmed that contamination risks were localised and controllable, rather than systemic across the works footprint, allowing the project to proceed without escalation to further investigation or remediation.
Recommendations and Risk Management
Based on the investigation outcomes, Confluence Environmental provided clear, proportionate recommendations to manage identified risks during construction.
These included:
Targeted handling procedures for slag-affected materials
Segregation of impacted soils during excavation
Integration of contamination controls into construction environmental management plans
Ongoing vigilance during earthworks to identify unexpected materials
Importantly, the recommendations avoided unnecessary escalation to broader investigation or remediation where it was not justified by the data.
Outcomes
The targeted investigation successfully resolved contamination uncertainty associated with the proposed substation upgrade and access works.
By addressing specific data gaps identified during the earlier PSI, the assessment provided the client with confidence that planned earthworks could proceed without triggering additional contamination constraints or regulatory delay.
The project progressed as planned, with contamination risk effectively managed through practical construction controls.
Why This Project Matters
Targeted contamination assessments play a critical role in infrastructure projects where broad site contamination is known, but only specific areas are subject to disturbance.
This project demonstrates the value of:
Focused, risk-based investigation strategies
Aligning investigation scope directly with construction activities
Avoiding unnecessary escalation where contamination is understood and manageable
Providing clear, contractor-ready recommendations
Confluence Environmental’s Role
Confluence Environmental provides independent targeted contamination assessments, Preliminary Site Investigations and construction support services for infrastructure and development projects across NSW.
Our approach focuses on resolving uncertainty efficiently, supporting construction delivery and maintaining regulatory confidence without unnecessary scope expansion.