Since undergoing cessation of production activities in 2014, the Chevron-operated facilities at Thevenard Island, Western Australia have been in a care and maintenance phase, with the site subject to campaign inspections and environmental monitoring. Onshore well plug and abandonment activities were completed in 2019, followed by some early-phase onshore decommissioning activities and waste removal.
In late 2020, Liberty Industrial was awarded the onshore decommissioning and remediation project through a competitive tender process – a project that intends to remove all asset infrastructure from the island, and restore those areas to a condition similar to and compatible with the adjacent nature reserve.
Most of the work completed on the island to date has been the removal of the three oil storage tanks and associated infrastructure, while the earthworks, land forming, and jetty removal work are set to begin this year.
Remediation works will follow on from the demolition phase and will involve the bioremediation of hydrocarbon impacted soils, the extent of which has been verified through the results of prior site investigations.
These soils will be excavated, blended with stabilised sand and then bioremediated on the island, after which the amended soil mixture will be placed into an excavated cell on site, below a depth of 1.5 metres from the final landform surface.
The final grade, or top 1.5-metre layer of the soil, must be free from any foreign materials, so all sands are being screened and all foreign inert materials (such as blue metal) removed.
This approach to remediation has been endorsed by the relevant regulators and provides a way to return the site to a state compatible with the nature reserve while being protective of environmental receptors and human health.
The project hasn’t come without its challenges. The island’s remote location and associated logistical movements have meant all equipment and materials are transported via roll-on/roll-off barge. Personnel are transferred via a passenger transfer vessel. There has also been a rigid focus on environmental and quarantine management throughout the project because of the island’s status as a nature reserve.
Five species of sea turtle inhabit the waters of north-western WA, with green, flatback and hawksbill turtles found near Thevenard Island. Work had to be carefully planned with consideration to the breeding cycle and movement of these species around the island.
Quarantine requirements for people, equipment, and materials have been crucial to prevent the introduction of new non-indigenous species or the spread of existing species and will be a key indicator for delivering successful project outcomes.
As the Chevron-operated project is now transitioning from a predominantly demolition phase to the earthworks and land forming phase, known wastes are now being segregated and disposed of off-site, such as waste materials within the evaporation pond.
Key works currently underway include final process area minor demolition works such as concrete and footing removal, remediation, final land forming, and jetty demolition.
Work completed to date includes:
- Demolition of three bulk crude oil storage tanks each with a 60 million litre capacity.
- Demolition of a 38-metre-high communication tower.
- Processing to export-grade of about 5,100 tonnes of ferrous scrap steel.
- 52 dedicated barge movements utilising high-sided scrap trailers for transport of ferrous scrap from the island.
- Removal of all underground services.
- Demolition of the redundant camp area, compressor facilities, and the flare pit and its surrounding infrastructure.
- Assisting in the removal of 15 production wells and 40 steel-cased wells.
- Removal of seven shore-crossing production lines
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