The National Offshore Petroleum Safety and Environmental Management Authority issued a reminder to the entire offshore sector saying that the Commonwealth had placed the responsibility for undertaking oil spill sampling solely with the titleholder, as they were the best placed to conduct sampling given the remoteness of offshore petroleum activities, but they needed to live up to their side of the bargain.
It reminded operators that proper sampling was needed to effectively identify the source of any spill.
"Samples of oil can be easily obtained for larger or continuous spill events where the source of the spill may be obvious," NOPSEMA said in a safety alert.
"It is also critical to obtain representative samples from minor oil spills or spills where the source is not immediately obvious.
"Sampling can be used to help identify the source of the oil spill by the elimination of credible spill sources. In this way, sources may be identified that would otherwise not be located when using other means."
NOPSEMA said operators should have appropriate arrangements in place for sampling, which is where ExxonMobil's Esso Australia business unit fell down.
While ExxonMobil reported the presence of the extensive sheen to the authorities, it was caught in the hop with a lack of effective sampling equipment.
Further, its staff were forced to improvise a method that did not align with good practice, and did not result in a useful sample that could be analysed in order to give a definitive result.
They also did not follow the appropriate sampling procedures in accordance with the accepted environment plan.
"This failure directly impacted on the titleholder's ability to identify the source of the spill or narrow down the range of potential credible spill sources," NOPSEMA said.
ExxonMobil has been served with an environmental improvement notice for its operations on the West Tuna platform.
It has 60 days to review its training methods to ensure staff know what to do, and ensure that all required equipment is located and maintained at West Tuna for future emergencies
NOPSEMA said proper identification was vital to ceasing the source of any spill, particularly where they were unclear and recurrent, and it could help similar spills from happening in the future.
