Natural degradation of hydrocarbons

About the project

NERA has entered the $3.07 million funding agreement with partners BP, Caltex, Santos, Viva Energy, Rio Tinto and CRC CARE to conduct a 3-year-long project that aims to verify the effectiveness of natural biodegradation of petroleum hydrocarbons at contaminated sites under Australian conditions.

Reducing costs of environmental recovery operations to promote growth and productivity while achieving best practice environmental outcomes for the energy resources sector is the aim of a collaborative agreement to facilitate regulatory reform in Australia.

Current regulatory requirements

Petroleum hydrocarbon contamination can be caused by oil spills, storage tank and pipeline leaks and other handling incidents. If the volume spilt is large enough, a 'pool' of hydrocarbon will form at the groundwater interface.

Risks from hydrocarbon releases include groundwater contamination and aquatic toxicity, as well as impacts to human health from exposure to hydrocarbon vapours and contaminated groundwater and soil. Site remediation occurs to mitigate these risks in situations where they are considered to be material.

Environmental regulatory policy varies between States in Australia and sometimes requires active recovery of petroleum hydrocarbon from contaminated sites, with an overall goal of zero hydrocarbon contamination in monitoring wells.

Petroleum hydrocarbons are complex mixtures of chemicals that variably partition into water and gaseous phases when released into subsurface environments.

Retention of residual hydrocarbon in the substrata and slow release to the monitoring wells mean that a goal of zero contamination is practically unachievable and may not be necessary to guarantee environmental protection.

Ongoing environmental recovery operations can continue for decades with ever diminishing recovery rates, incurring huge costs with no environmental benefit. This can also unnecessarily delay decommissioning and relinquishment of titles for onshore oil and gas production and storage facilities.


To date, there has been a limited understanding of the rate of natural biodegradation of hydrocarbons in contaminated soils in Australia. Whilst natural attenuation into groundwater has been well studied, the importance of natural degradation of hydrocarbons into gaseous components in soils and underlying strata (termed Natural Source Zone Depletion) has only recently been recognised. Current regulatory approaches are beginning to acknowledge the effectiveness of the process and associated monitoring technology.

The rates of biodegradation that can be achieved under Australian conditions and the sustainability of the processes have needed to be verified. If the biological processes can be proven to be sustainable, there is a strong case for gaining regulatory acceptance of relying on biodegradation once monitoring has indicated active recovery is no longer beneficial.

The project is nearing completion and the results have been very encouraging. A technical guide on how to estimate Natural Source Zone Depletion (NSZD) has been published by CRC CARE as Technical Report 44. Studies by CSIRO of six contaminated sites in Australia indicate that NSZD rates can be very significant. This report, together with a management guide on how to take NSZD into account in remediation design, will be released toward the end of 2019. The regulatory community has been engaged throughout the life of the project to ensure the technical and management guidance documents are acceptable and suitable for rapid uptake into state policy frameworks.

NERA's Sector Competitiveness Plan identifies regulatory framework optimisation as a knowledge priority for the energy resources sector, and this project aims to address this priority.

Project Partners

Project Funding

Total Project Cost: $3,057,000

NERA: $644,000

Industry: $1,125,000

In Kind Support: $1,288,000