NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: contaminants, water quality, mining impacts, arsenic, climate change

Objective(s): The long-term objective of this research is to determine what processes control the recovery of the landscape near Yellowknife that was contaminated by stack emissions from the Giant Mine roaster, and how this recovery will be affected by climate change and unusual or severe weather events. One focus will be on how climatic events, especially sudden rainfall or snowmelt, affects how arsenic is transported from the soil through runoff into lakes. Another focus will be on how arsenic in the soils changes over time, and whether those changes in mineral host results in increased mobilization of arsenic from soil to surface water, or enhanced sequestration of arsenic in the soil. The expected outcome is a better understanding of the long-term stability of arsenic on the landscape, and how long it will take to recover from the contamination associated with mining and ore processing. These results will be valuable to decision-makers with regard to land use planning and the prediction of surface water quality. They will also be helpful in providing information to Yellowknife, Ndilo, and Dettah residents about the health of their environment and how this may change over time.

Project Description: This licence has been issued for the scientific research application No.5534. The long-term objective of this research is to determine what processes control the recovery of the landscape near Yellowknife that was contaminated by stack emissions from the Giant Mine roaster, and how this recovery will be affected by climate change and unusual or severe weather events. One focus will be on how climatic events, especially sudden rainfall or snowmelt, affects how arsenic is transported from the soil through runoff into lakes. Another focus will be on how arsenic in the soils changes over time, and whether those changes in mineral host results in increased mobilization of arsenic from soil to surface water, or enhanced sequestration of arsenic in the soil. The expected outcome is a better understanding of the long-term stability of arsenic on the landscape, and how long it will take to recover from the contamination associated with mining and ore processing. These results will be valuable to decision-makers with regard to land use planning and the prediction of surface water quality. They will also be helpful in providing information to Yellowknife, Ndilo, and Dettah residents about the health of their environment and how this may change over time. This project will involve multi-season fieldwork and laboratory analysis of water and soil samples. The research team will be working in a subcatchment of Pocket Lake close to Giant Mine and accessible via the Ingraham Trail. This is a highly impacted area, and the easy access means that the team can sample throughout the open water season and respond quickly to high rainfall or sudden snowmelt events. The fieldwork will involve two graduate students from Queen’s University, one of whom will spend most of the snowmelt and open water season in Yellowknife. A field assistant will be will take part through the Yellowknives Dene First Nation for the duration of field work. Field support will be provided by co-PI Palmer, who is a Yellowknife resident. This will also provide multiple opportunities for communication with communities and residents. The primary pathway for terrestrial materials to enter lakes in the subarctic shield terrain around Yellowknife is through snowmelt runoff but changing precipitation conditions associated with climate change may be altering this pattern. Changes in the magnitude and timing of rainfall events will alter flow paths and the amount of water running off the landscape, thus influencing the amount of arsenic running into lakes. This project will provide important information on the cumulative impacts of arsenic contamination of regional soils and climate change on landscape recovery in a region impacted by 60 years of mining emissions. 1. Climate and precipitation measurements Surface and subsurface runoff is primarily influenced by precipitation; therefore it is important to measure the amount, timing, phase, and chemistry of precipitation that falls in the study area. The research team will capitalize on existing climate station infrastructure maintained by Environment and Climate Change Canada and the Government of the Northwest Territories-Environment and Natural Resources in the study catchment to measure important climate parameters, such as rainfall, air temperature and snow depth. Additional snow depth and density measurements will be made across the catchment in late-winter to estimate the snow-water equivalent available during snowmelt. Rain and snow will be collected for chemical analyses. 2. Characterization of soils The mobilization of arsenic from soils is dependent on how the arsenic is hosted (i.e. what minerals it is associated with). Detailed soil sampling and mineralogical analyses will provide important information on the soil physical and chemical properties (bulk density, soil texture, porosity and organic matter content) and type of arsenic that exists in the soil profile and whether the arsenic trioxide is converted to a less mobile compound with depth and over time. The presence and persistence of decades-old arsenic trioxide in soils and lake sediments is surprising given the high solubility of arsenic in the baghouse dust and is likely due to kinetic factors. The possibility of passivation by fine-scale alteration rims will be explored as part of the proposed mineralogical research. The methods used will include electron microprobe analysis (EMPA) and scanning electron microscopy (SEM). Quantitative mineralogy based on SEM measurements will provide information on all types of arsenic-hosting solid phases, even rare and fine-grained particles. The research team have optimized these methods for arsenic-contaminated soils in previous studies. The team will also undertake a comprehensive soil survey to quantify the amount of arsenic present throughout the catchment. 3. Surface runoff sampling Surface runoff will be quantified using a series of V-notch weirs that have been installed in different landcover types in the catchment and at the basin outlet. Water samples will be collected daily during surface runoff events to measure important chemical parameters of surface runoff with more intensive sampling during peak runoff periods (e.g. following large rainfall events) to characterize the diel variations in flow volumes, arsenic concentrations, and hydrological flow paths. Combining flow and concentration data from different landcover types (bedrock outcrops, treed bedrock areas, peatlands, and soil filled valleys) and at the basin outlet will allow the team to estimate arsenic mass transport across the catchment, and to assess the relative contribution of different landcover types and runoff events to the mobilization of arsenic from the catchment to surface waters. 4. Subsurface water sampling Soil waters will be sampled with suction lysimeters installed at different depths throughout the catchment to characterize soil water conditions. The research team have used these instruments in the Yellowknife area before and in many other studies. They will be in place throughout the project and allow for repeated collection of soil pore water. These will be sampled every 2-3 days during snowmelt runoff, the day after major rainfall events, and as frequently as soil moisture conditions allow for adequate volumes to be recovered for the required chemical analyses in between precipitation events. Chemical analyses of water, rain, and snow samples will include total and dissolved arsenic, arsenic speciation, dissolved organic matter characterization, total dissolved nitrogen, the stable isotopes of water, and major ions. The water stable isotopes combined with major ions and dissolved organic matter chemistry will allow the team to identify the water sources (rain, snow, and subsurface waters) as well as the hydrological processes and pathways responsible for delivering the arsenic at different times of the year, and to determine the seasonality of arsenic loads in runoff. The research team anticipate a comprehensive dataset of precipitation, surface runoff and soil pore water analyses that indicate how water quality changes in the soil environment (including subsurface) will influence delivery of arsenic to lakes over time. This will be complemented by detailed soil analyses that will focus on how arsenic is mobilized or sequestered. Regular meetings will take place with local decision-makers and community governments for initial input and to report progress. These will be in-person, virtual or hybrid meetings depending on the COVID-19 protocols at the time. Results will be presented at conferences in the NWT and across Canada. Project results will also be published in student theses and scientific publications. A project summary will completed as a plain language report to the NWT Geological Survey (Open File report). The fieldwork for this study will be conducted from April 17, 2023 to December 31, 2023.