Following a blowout at the Montara wellhead platform on 21 August 2009, petroleum hydrocarbons flowed effectively unabated into the Timor Sea, approximately 175 kilometres (km) from Western Australian coastal waters, until the leak was contained on 3 November 2009. This report presents findings of a petroleum hydrocarbons survey conducted in July 2010 as part of the response to the Montara incident.
The aim of this survey was to determine the petroleum hydrocarbon content of shoreline sediments and filter feeding organisms some eight months after the flow of hydrocarbons from the Montara wellhead platform was stopped in order to assess the intensity, extent and duration of potential Montara oil-related contamination. To this end, data were collected to allow direct comparisons with baseline data collected during an earlier survey in October 2009 (McAlpine et al. 2010). The July 2010 survey involved sampling shoreline sediments and intertidal rock oysters at seven Kimberley islands and two mainland promontory sites visited by McAlpine et al. (2010). Cultured pearl oyster tissue samples were also collected from the four pearl farms visited in October 2009 (McAlpine et al. 2010). There were no detectable concentrations of petroleum hydrocarbons found in any of the shoreline sediment or oyster tissue samples collected during this survey. This result was consistent with the findings of the baseline survey (McAlpine et al. 2010).
In view of the overall consistency of the results, spatial coverage of the surveys and the lack of evidence of any recent oil impacts at any of the sites, it is likely that if any oil from the Montara spill reached the coastal waters of the Kimberley region, the resulting impact on the coastal environment would have been transitory and at levels that could not be detected by the sampling methods used in these surveys. The values reported in this survey and the previous baseline survey are therefore considered to broadly represent readily-measureable natural background petroleum hydrocarbon conditions in this part of the Kimberley marine bioregion.
The findings of this survey as well as the 2009 baseline survey also suggest that natural petroleum hydrocarbon seeps in the Timor Sea do not appear to have a readily measureable chronic or residual effect on the quality of the Kimberley marine environment at the sites investigated.
These data will be of value to all stakeholders for assessing potential impacts of future development and monitoring the quality of the marine environment in the Kimberley bioregion.