Advances in remediation science and a developing local expertise have allowed Australian scientists and engineers to begin addressing long-term soil contamination issues at Australia’s Antarctic and subantarctic stations.
Since 2003, remediation teams have applied and modified existing remediation technologies, normally used under warmer, more favourable conditions, to clean up fuel spills and develop risk and remediation guidelines for Australia’s Antarctic and subantarctic stations and environments. The work will be used to assist other Antarctic nations in their remediation efforts and to tackle legacy sites such as Australia’s abandoned Wilkes station.
At Casey station, members of the Australian Antarctic Division’s remediation team have delivered a significant and ongoing decrease in soil contamination at the station over the past four years. The first stage of the Casey clean-up began in 2005, to deal with a 6000 litre fuel spill at the station’s main powerhouse in 1999. The remediation team, in collaboration with scientists from the University of Melbourne, installed a ‘permeable reactive barrier’ (PRB) at the site. These barriers prevent fuel-contaminated snowmelt and groundwater from leaching into the surrounding environment, by channelling it through a treatment system.
‘PRBs are the first step in a multi-step process used to treat a contaminated site,’ Australian Antarctic Division Remediation Specialist, Mr Tim Spedding, said.
‘PRBs contain the effects of a spill and minimise the spread of contamination until the site can be more actively remediated. You need to install them first because once you start excavating contaminated soil for treatment you’ll also thaw the ground and remobilise a lot of the contaminants in the meltwater.’
The PRB consists of a series of cage pallets containing pelletised nutrients and activated carbon, which is placed in the path of the meltwater flow. When the water enters the barrier it becomes enriched with nutrients, which stimulates the native soil microbes to begin degrading fuel captured on the activated carbon. After a further nutrient capture step, clean water flows out the other side of the barrier.
In Antarctica the environmental conditions are such that PRBs can only passively treat contaminated meltwater, rather than actively reduce soil contamination. So in 2010 the team embarked on an active approach to remediation by excavating the contaminated soil and creating a series of ‘biopiles’. Like PRBs, biopiles use the native soil microorganisms to break down fuel contaminants. They do so at a faster rate, however, because the soil conditions are optimised for microbial growth by the addition of air and moisture.
Over three summer seasons, seven biopiles have been built at Casey station, with each soil pile measuring some 18 x 5m in size and 1.5m high. The biopiles are active for up to three months a year, when summer temperatures are high enough to thaw the soil and release moisture. Once the soil is thawed, leachate water is re-circulated through it to increase soil moisture distribution. A system of aeration pipes forces air through the biopiles towards a carbon filter at one end, trapping any volatile compounds that then biodegrade or evaporate.
While the technology has been used extensively in the Arctic and temperate environments, Antarctica has different environmental conditions and soil types. As a result, the team has had to research and tweak their materials and methods while they work. Part of this process involved testing a variety of materials used to cover and to line the base of the biopiles. To do this, the remediation team recruited geoenvironmental engineer Dr Rebecca McWatters, from Queen’s University, Canada, for her expertise in Arctic contaminated sites, geosynthetic materials and barrier systems.
‘For the past three years we’ve been investigating different combinations of geosynthetic liner materials on the biopiles, to test their long-term performance as a composite barrier system in preventing the movement of contaminants out of the biopiles and into the environment; all while the soil was being treated,’ Dr McWatters said.
‘We’ve also trialled a range of geotextile covers, which prevent contaminated dust being blown off the biopiles.
‘We’re looking for the right combination of technologies that will do the job with minimal cost, maintenance and management, and that will outlast the lifespan of the contaminated soil.’
The tests were conducted on the biopiles while soil remediation was underway, but also in a variety of other field- and laboratory-based tests. By early 2014 the team had supportive evidence for a combination of materials that would do the job while withstanding the cold, dry, windy, abrasive and UV-intense environment. In the process, the team also significantly remediated the contaminated soil.
‘Our most recent tests show that hydrocarbon concentrations in the biopiles are decreasing by 50% every 500 days,’ Dr McWatters said.
‘This compares to no detectable change over five years when just the PRB technology was used to contain the contaminants on site. This is very exciting and shows we are nearing our goal of returning remediated soil to the Casey environment for specific reuse applications.’
But how clean is clean enough? That is the question now occupying the remediation team and ecotoxicologists at the Australian Antarctic Division (see How clean is clean enough?). While the soil will never return to its original state, there will be a point beyond which the effort to continue remediation will be disproportionate to the risks posed to the environment’s flora and fauna.
While the ecotoxicology work is still in progress, Mr Spedding said the remediation team has enough scientifically sound remediation options and technical expertise to begin to address clean-up issues at more difficult sites.
‘And through the Antarctic Treaty system we’ll be able to pass on what we’ve learned to other nations, so that they can apply it without having to go through the lengthy tests and trials we’ve already undertaken,’ he said.
Corporate Communications, Australian Antarctic Division