Published on Australian Maritime Safety Authority (https://www.amsa.gov.au)
The tanker was moored, in preparation for receiving a load of crude oil from storage tanks on the island via a subsea pipeline, when a pollution incident occurred.
Varanus Island is located in the offshore waters of the North West Shelf in Western Australia, approximately 60 km from the coast.
During preparation for loading, a crane on the tanker was being used to raise the loading hose from the seabed in order to connect it to the tanker’s receiving manifold. As a result of earlier bad weather, a length of chain had become entangled around a subsea purge valve. As the crane exerted more pressure to lift the line out of the water it sheared off the purge valve resulting in a hole in the pipeline.
The feed from the storage tanks on the island was immediately isolated via a shut in valve, however crude oil contained in the section of the subsea pipeline free flowed from the damaged purge valve to the ocean. A dive team was then mobilised to manually close the main subsea shut off valve. This isolation was achieved 12 hours after commencement of the spill.
Investigating officers from the then Department of Minerals and Energy (DME) concluded an estimated 25 cubic metres of oil was released to the environment. An oil spill response was initiated following the company’s approved Oil Spill Contingency Plan.
Notification of the spill was given to relevant government authorities, a pearling operation located to the north, community conservation groups and the fishing industry.
The spill was monitored by the company using helicopter aerial surveillance, marine vessels and oil spill trajectory modelling.
On 27 July surveillance was undertaken by personnel from the then Department of Environmental Protection (DEP) and the DME. Results indicated that the spill had remained offshore and had progressively weathered from free oil to a patchy mousse composition within three days. By the fifth day, only ribbons of sheen were present on the sea surface and no oil was observed by the sixth day after the spill.
Extensive surveys along with further sampling and chemical analysis of water, beach sediments and oysters confirmed no recordable impact to any of the Lowendal and Montebello Island groups.
Read about Australia's National Plan for Maritime Environmental Emergencies.