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Update 2020/3/23 Teachers' Hub
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FUEL MUNCHING MICROBES & BIOPILE LINERS – QUEEN’S RESEARCH IN ANTARCTICA
By Suzanne Forcese
Australia’s Casey Station, a year-round research station located 4000 km south of Perth is the largest bioremediation construction site in Antarctica, holding 750 cubic metres of contaminated soil.
For two seasons, Vanessa Di Battista, PhD student in the Department of Civil Engineering at Queen’s University has been investigating the performance of geosynthetic that contain soil undergoing remediation.
Battista, who had returned to academia at Queen’s after a two-year industry stint as a tailings dam designer, spoke with WaterToday about her “full circle moment” in the first-ever successful use of remediated soil in Antarctica. It was a contributing factor in the research project that will go down as one of the highlights of her career.
“Everything about my journey has been a fluke,” Battista said regarding the fact that she decided to enroll in engineering the day before classes began; the fact that her time in industry was to be short-lived because of cut-backs; the fact that she was accepted into the geoenvironmental PhD program without a Masters; and the ultimate good fortune of being on the team collaborating with the Australian Antarctic Division at Casey Station. Her first year involved studying and testing liner materials sent to Canada from the Casey biopiles.
Biopliles are mounds of fuel-contaminated soil that rely on native soil organisms to break down the fuel.
“I love the idea that an engineer has a social responsibility to protect the environment and public good. Soil remediation and design became my passion. I’m the third of Dr. Kerry Rowe’s students involved in the remediation of contaminated soil in the Antarctic.”
One of the realities of a year-round research station in the Antarctic is the generation of on-site power. “Casey generates all its power using diesel generators and it stores about one million litres on site every year. Unfortunately, spills can be expected with the most recent being thirty years ago.”
Under the terms of the Antarctic Treaty all countries operating in the Antarctic are now committed to environmental protection. The protocol specifies that all newly generated waste should be removed from Antarctica and member countries are obliged to remove old waste unless the action of removing waste creates a greater adverse environmental impact.
Removal of Antarctic soils may not be the best environmental solution. The Queen’s team is focusing on containment and on-site remediation.
Native Antarctic microbes are being used to clean up contaminated soil by breaking down and recycling petroleum hydrocarbons.
“The night before I arrived at Casey there was a 6,000 litre fuel spill in a critical location where a building had to be constructed before the season’s end. There was diesel in the groundwater. We had to remove all the contaminated material and regrade the site for construction to begin.”
The source contamination was removed but further contamination had to be prevented in the creation of a new biopile. To contain the soil and prevent fuel from leaching out while it is undergoing treatment, a composite liner system was used beneath the biopiles.
The system consists of a clay liner sandwiched between two geotextiles. A heavy duty plastic sits on top of the clay liner and adds an additional barrier against the migration of contaminants from above. Finally, a geotextile helps protect the plastic from being punctured by any rocks in the biopile soil.
“At the same time, we had to fill the pit with something. We used material from a decommissioned biopile to regrade the site.” The biopile was built in 2010 and decommissioned in 2018. “This was the first time remediated soil was used in Antarctica. It was a full circle moment.”
Geomembranes (GMBs) and geosynthetic clay liners (GCLs) are used worldwide to prevent contamination. An important part of Battista’s work is to monitor the liner system throughout the soil remediation process to ensure it is performing as designed in the relatively untested Antarctic conditions. While the plastic liners are good at stopping fluid migration they can get punctured by rocks in the soil.
“Over time these punctures can become holes.” The clay liners self-heal if they’re punctured but they operate best at about 60% hydration. As Antarctica is essentially a desert the clay liner can often be unevenly hydrated or dessicated.
In the first 5 years of biopile operations the team included small coupons of each material beneath them which they removed each year to see how they changed in response to freezing, thawing, puncturing by rocks and exposure to contaminants and UV light. Tests are essential to demonstrating that these materials are performing as intended and preventing fuel contaminants from entering the environment.
“We used to send our clay liner samples back to Queens to x-ray but that meant we couldn’t do the sampling in real time.”
Inspiration hit with the realization that there was a medical x-ray in the camp’s on-site doctor’s office. “We were all so healthy at the camp so there was very little for the doctor to do and he was quite happy to be of assistance.”
Chief Medical Officer, Dr. Jeff Ayton obtained the required approvals from the Australian Radiation Protection and Nuclear Safety Agency for the station doctors to use the medical diagnostic X-ray equipment to analyse scientific samples. Now moisture content and structural change in samples can be immediately determined resulting in greater accuracy.
“What struck me was the great variation in hydration and the migration of fine soils.” It soon became apparent the bentonite content in the liner of the GCL is more important to performance than intemperate conditions. It was also observed that the preparation, hydration and drainage of the subgrade on which the biopiles sit is critical.
Battista’s design involved a sub-grade preparation where mechanically sieved subgrade was placed on the geotextile separator to achieve better hydration and prevent migration of fine materials that were observed in the decommissioned biopile. “Self-healing was detected with the x-rays showing us that subgrade conditions have noticeable effect on GCL hydration.”
The work of Battista and the rest of the team is relevant for future clean-up projects and any engineering project where geosynthetics are used in the Antarctic.
As for the Antarctica experience Battista adds, “It completely changed me. I came back to Canada a different person. I discovered who I am.”
Vanessa Di Battista will continue her career in research (next stop the Arctic) and teaching at Queen’s University-- still loving her responsibility to protect the environment and the public good.
Queen’s University PhD Student Vanessa Di Battista
suzanne.f@watertoday.ca
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