Hydro Aluminium Kurri Kurri Smelter

The Hydro Aluminium Kurri Kurri (HAKK) Smelter was one of six smelters producing aluminium in Australia until closure in 2012. Since this time, Hydro has embarked on a decade-long campaign to meet its environmental obligations for decommissioning, demolition and decontamination to the highest standards.

In our effort to help our client achieve sustainable change, Ramboll completed all the environmental investigations at the Smelter Site and the surrounding Buffer Zone, which includes valuable biodiversity. The driver for remediation was long-term stockpiling of aluminium smelter waste at the site, which had led to a leachate plume impacting shallow groundwater and vegetation growth in a portion of the Buffer Zone.

Ramboll finalised the Remedial Action Plan (RAP) in 2018 with on-site containment of aluminium smelter wastes and contaminated soil in a purpose-built Engineered Containment Cell (ECC) designed to the highest engineering standards selected as the remedial solution. As part of the remedial options assessment, Ramboll completed a Net Environmental Benefit Analysis (NEBA) which identified on-site containment as the most sustainable remediation option.

Implementing the RAP has involved multi-disciplinary teams completing several separate but interlinked projects:

• Removal of process wastes, including dusts, residues and hazardous materials during decommissioning works
• Remediation of Buffer Zone properties, including a former municipal landfill
• Remediation of accessible contaminated soil during demolition works
• Interim storage of process wastes and contaminated soil
• Remediation of remaining contaminated soil
• ECC construction, filling and capping

Ramboll led environmental investigation, remediation and validation works, including iterative investigations for a range of contaminants of concern associated with aluminium smelting, namely fluoride, petroleum hydrocarbons (TRH/BTEX), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Ramboll progressively completed validation reporting as remedial works at the Smelter Site and in the Buffer Zone were completed.

In the past, decommissioning, demolition and decontamination of major industrial facilities have been completed as separate projects with divergent objectives. At industrial facilities where soil contamination has been retained and capped, decontamination of subsurface infrastructure has not been required. This has led to long-term management requirements and can impact future redevelopment opportunities.

At the HAKK Smelter, the objective of the RAP was to render the former smelter suitable for future industrial land use with no long-term management requirements. This requirement led to innovative engineering solutions that have contributed to both technical knowledge and contracting processes within the contaminated land profession.

During decommissioning and demolition works, Ramboll and the demolition contractor implemented the requirements of the RAP but went beyond these requirements to develop a more formalised methodology that allowed provision of required information for validation reporting. Three main contamination risks required management during decommissioning and demolition works:

• Minimising potential for cross-contamination of surface soil, surface water and groundwater during removal of hazardous materials
• Validation that retained subsurface infrastructure had not caused contamination that required remediation and did not contain contamination sources
• Validation of generated crushed concrete that was used as backfill on-site

Over 80 separate Work Method Statements were developed and implemented, taking 150,000 work hours over four years with zero lost time injuries.

Specific Validation Reports were prepared for different contaminants of concern, including a Subsurface Asbestos Validation Report for remediation of bonded and friable asbestos used in subsurface infrastructure; a Substations Validation Report for remediation of PCBs associated with leaking transformer oil; a Carbon Plant Validation Report for remediation of PAHs associated with production of carbon anodes and a Technical Services Validation Report for remediation of TRH associated with leaking fuels and oils at mechanics workshops.

Ramboll also prepared a Demolition Validation Report, which reported on the sequencing of decommissioning and demolition works; works completed to validate the suitability of retained subsurface infrastructure; validation sampling of over 260,000 tonnes of crushed concrete; tracking of materials across the smelter site to confirm contaminated materials were relocated to the ECC while uncontaminated were reused as backfill and off-site tracking of PCB-contaminated materials to confirm lawful disposal.

At the completion of demolition works, Ramboll and the demolition contractor created a digital twin of subsurface infrastructure remaining below 1.5 m bgs, including retained concrete pits, footings and services. The digital twin was developed using Hydro engineering drawings covering the layout of the entire former smelter, with a link to these drawings in a GIS database.

This digital twin provides useful information to the site developer, who will be able to plan the new subdivision layout and new services around retained subsurface infrastructure. This will reduce risks with unknown ground conditions in the future.

Ramboll maintained a full-time site presence during the final year of demolition works, which was completed in conjunction with remediation works and cell filling. Our consultants were able to supervise remediation works and be reactive to unexpected finds to ensure seamless completion of final demolition works and filling of the cell.

Sequenced preparation of comprehensive validation reports resulted in the early sale of a portion of the former smelter for redevelopment as part of the Hunter Power Project. This milestone could not have been achieved without a technically capable multi-disciplinary team focused on delivering a high standard of remediation engineering.

The lessons learnt on this project can be carried forward to provide a framework for best practice decommissioning, demolition and decontamination of other large-scale industrial facilities into the future.