On 15 January 2010, a helicopter was carrying a sling load of three 200-litre drums of special Antarctic blend (SAB) diesel fuel from Davis Station to a nearby aircraft ski-landing area. The load became unstable and, for the safety of the aircraft and personnel, it was released from a height of approximately 60 metres. The drums ruptured on impact, and the fuel seeped into sandy soil adjacent to Lake Dingle.
The initial response was conducted in accordance with the station fuel spill contingency plan, and a response team with spill equipment was at the site within an hour.
While the initial efforts were under way to contain and remove the contamination source, a multidisciplinary team assembled to assess the site and work out the best clean-up options.
Considering the environmental values of the site and the options available for clean-up, it was decided to remove all soil contaminated with more than 100 milligrams of fuel per kilogram of soil (mg-fuel/kg-soil) from the site and to remediate it in a contained treatment cell referred to as a ‘biopile’.
In early 2010, approximately 130 tonnes of excavated soil from the spill site were flown by helicopter to Davis Station. In the following season (2010–11), an additional 38 tonnes of soil were removed from the impact point using a portable vacuum suction unit driven with compressed air.
A detailed soil and water sampling program was conducted to assess the spill site after excavation works. No samples with fuel concentrations above the 100 mg-fuel/kg-soil target were detected, and there was no evidence of fuel contamination in Lake Dingle or in waters migrating from the spill site towards the lake.
The biopile was designed and built using materials typically used in engineered landfill designs. The barrier had 3 layers of material, providing a superior barrier and confidence that the hydrocarbon contaminants were being contained within the biopile. A geotextile cover was placed on top of the contaminated soil in 2013 to prevent dust migration and provide a barrier between the soil and animals (e.g. elephant seals). To improve the natural breakdown of hydrocarbon contaminants by native microorganisms, a mixture of nitrogen, phosphorous and potassium was added to the biopile.
Managing the biopile included removing excess water that accumulated from the snowmelt each season from inside the biopile, to prevent water from spilling over the containment barriers and potentially contaminating the surrounding environment. The operation also included aerating the soil each year by turning it with an excavator. The soil and leachate were sampled every year to measure nutrient (fertiliser) and fuel concentrations, the latter of which decreased each year.
Ongoing soil analysis confirmed that, by late 2014, contaminant concentrations in the biopile soil were at a level where the soil could be re-used for building footings. This is a site-specific and use-specific re-use option for the remediated soil. Remediated soil not used for building footings is kept on station, and any alternative re-use will require further risk assessment specific to the proposed re-use option.
The clean-up of the Lake Dingle fuel spill is the first example of the remediation and re-use of fuel-contaminated soil onsite in Antarctica. Soil is a valuable and scarce resource in Antarctica, and this approach was used to offset the environmental impact of soil excavation required for infrastructure works.