Characterization of Arsenic Species in Lake Sediments Surrounding Giant Mine, NWT.

Martin Didier Van Den Berghe, Queen's University, Geological Sciences and Geological Engineering, Kingston, ON, Canada, Heather Jamieson, Queen's University, Kingston, ON, Canada and Mike Palmer, Government of the Northwest Territories, Cumulative Impact Monitoring Program, Yellowknife, NT, Canada

Contact First Author: Martin Didier Van Den Berghe; martin.vandenberghe@gmail.com

Previously Published Material: This presentation was first shown at the Yellowknife Geoscience Forum (Yellowknite, NT) in November 2014.It will also be presented at the Gananoque Environmental Engineering and Science Conference (Gananoque, ON) in February 2015.

Abstract ID#: 33854

 

English Abstract:
Giant Mine is was gold mine a few kilometers north of Yellowknife, NT that operated between 1948 to 1999. Roasting of arsenopyrite at Giant Mine released approximately 20,000 tonnes of arsenic aerosols to the environment from roaster stack emissions, 86% of which was released in the first 14 years of operations. Recent studies have shown elevated levels of arsenic in lake sediments beyond the boundary of the property, raising questions about their origin and associated risks to local ecosystems and public health.

The purpose of this study is to determine whether the arsenic present in regional lake sediments is of natural or anthropogenic origin, and whether these lakes act as a sink (capture) or a source (release) of arsenic in the overlying lake waters. This may be done by assessing the speciation of arsenic in both lake sediments and associated porewaters using dialysis arrays, major and trace elements analysis, synchrotron-based analysis, and advanced scanning electron microscopy. From there we can evaluate the relative stability of arsenic species in these different chemical media, and thus establish the long term trends of arsenic in the aquatic environment.

A field program was completed in July 2014 during which three local lakes were sampled downwind of the roaster stacks. These lakes offer a range of physical and chemical characteristics such as lake depth, organic contents and nature of substrate and immediate catchment. Focusing on these lakes will allow us to better constrain various physical and chemical parameters of lakes geochemistry in relation to arsenic mobility.

Preliminary results of this program indicate arsenic concentrations in sediment porewaters range from 80 to 1,600 parts per billion, consistently peaking 2-6 centimeters below the sediment-water interface. This might indicate a trend for arsenic to remobilize and migrate upwards through the sediment column after deposition. Whether this remobilized arsenic gets released into the lake water or gets trapped into a more stable mineral phase has yet to be determined.

Understanding the sources and behaviour of arsenic in such lakes is very important in understanding contaminated site attenuation and remediation efforts, helping constrain chemical behaviour of contaminants, and associated health risks to ecosystems and Human populations.

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