Extensive field-based research was undertaken to better understand the remediation processes.

Improving processes for flushing contaminants from groundwater

Research conducted at CSIRO Land and Water has significantly improved the process and design of groundwater remediation systems using air sparging and multiphase extraction.

• 31 December 2009 | Updated 14 October 2011

• The challenge 
• The response 
• The outcome 

The challenge

Water supplies in urban and industrial environments are prone to biological, chemical and radiological contaminants which can affect supplies for drinking water and irrigation.

Benzene and other constituents of petroleum hydrocarbon fuels can cause significant and wide spread contamination of groundwater through fuel spills. These are particularly problematic since components of the spilled fuel distribute into soil, water and air phases underground, posing a range of exposure risks to human health and the environment.

Many remediation approaches, particularly those that pump and treat groundwater have been ineffective and costly.

In-situ air sparging (IAS) (injecting air below the water table) and multiphase extraction (MPE) (pumping out the contaminated air, water and fuel phases from below ground) have recently been used to treat petroleum spills.

However, these methods have been hampered by lack of understanding about their effectiveness and the processes involved, preventing them from being appropriately and cost-effectively applied.

The response

In response, CSIRO Land and Water undertook field-based research to better understand the processes involved with IAS and MPE, including:

• the distribution of injected air in aquifers
• the effectiveness of multiphase extraction wells
• the vaporisation and aerobic degradation of contaminants.

The research involved intensive monitoring and analysis of:

• air distribution in aquifers
• dissolved contaminants
• fuel mass recovery and loss
• aerobic biological activity
• the concentration of vapours of concern in soil gas and the extracted air.

Results showed that air sparging removed the prime contaminants of concern (benzene, toluene, ethylbenzene and xylene) from groundwater in sandy aquifers within hours to days via vapourisation.

The process also effectively removed a number of other aromatic compounds and constituents of gasoline.

However, other elements of dissolved petroleum hydrocarbons were more reliant on continued biodegradation from stimulation of aerobic bacteria by oxygen in the injected air.

Multiphase extraction trials showed increased benefits of extracting each of the air, water and fuel phases to recover a fuel spill, compared to just recovering the fuel phase itself.

The outcome

CSIRO's research and findings have significantly improved the process and design of remediation systems using air sparging and multiphase extraction, resulting in multi-million dollar operational savings for industry.

In addition, the reduced risk to human health and improved protection of the environment is of great benefit.

The team is now investigating the feasibility of biosparging, a variation of IAS in which the fuel vapours are treated below ground before they escape into the atmosphere.

Ongoing research into multiphase extraction is also taking place, to maximise the effectiveness of the process in more challenging underground environments.

The knowledge gained from the research has also supported the development of other air-flushing remediation technologies aimed at various organic liquid source contaminants.

Find out more about our research in Urban water: urban water environments.