Horizon Power Redundant Power Station Site Remediation

Location: Onslow, Exmouth, Fitzroy Crossing, Meekatharra, Cue, Mount Magnet and Wyndham
Client: Horizon Power
Role: Lead remediation contractor
Status: Completed 2020
Project Team: Demolition and Remediation team
Project Director: Stephen King
Project Manager:
Site Supervisor: Bernie O’Rourke
Site Team: Various

Detailed Project Description:

Merit was engaged as the remediation contractor to remediate several power stations in regional locations comprising Onslow, Exmouth, Fitzroy Crossing, Meekatharra, Cue, Mount Magnet and Wyndham. Merit subsequently engaged Aurora to act as their Environmental Consultant to assist with and document the remediation works.

Six of the seven sites had previous investigations with varying degrees of confidence as to the extent of remediation works that would be required. Four of the sites were also being deemed as Source Sites under the Contaminated Sites Act and required contaminated sites auditor involvement and approval.
Based on data from previous investigations a Remediation Action Plan (RAP) was prepared for each site. The RAP also contained aspects of a Sampling and Analysis Quality Plan (SAQP), Environmental Management Plan (EMP) and Bioremediation Management Plan (BMP) to achieve the client’s site specific project objectives. The overall project objective was achieving a suitable end-point classification for each site under the CS Act.

Taking into account the regional nature of the sites, costs, net environmental benefits Aurora determined in consultation with Merit and Horizon Power that the most effective approach to remediating the diesel impacted soils at five of the sites was to excavate the impacted soils and facilitate enhanced bioremediation until they were deemed suitable for reuse onsite.

As the extent of impacts had not been fully delineated and considering the remote nature of the sites, the extent of remediation was determined based on field observations (visual and olfactory evidence) supported by volatile organic carbon readings recorded by a handheld photoionization detector (PID). Validation samples were also collected to verify the extents of the excavation had been achieved, which was deemed to be a successful approach.

Upon receiving analytical data characterising the stockpiled impacted material, the nutrient and moisture requirements to facilitate enhanced bioremediation were calculated. With the stockpiles subject to tilling until the qualitative assessment criteria was achieved and deemed suitable for reuse. Approximately 3,800m3 of diesel impacted soil was successfully remediated for reuse across the sites.

In addition to the planned remediation jobs, Merit/Aurora also implemented emergency remediation works at one of the power stations implementing the processes and procedures used at the other remediation sites. Approximately 4,000L of diesel was spilled, which moved approximately 150m offsite towards a sensitive receptor. A short Environmental Notification Form (ENF) documenting the works implemented was prepared and provided to the Department of Water and Environmental Regulation (DWER). Based on the ENF DWER were satisfied with the extent of remediation works and did not require an auditor to be engaged even though there were offsite impacts.
Site Management Plans (SMP) were also prepared for four of the six sites to manage risk from minor residual soil impacts that could not be effectively remediated.