Understanding regional variability in soil geochemistry in an area impacted by legacy industrial activity

Regions: North Slave Region

Tags: contaminants, geology, arsenic, industrial development, soil chemistry

Principal Investigator: Oliver, Jonathon (1)
Licence Number: 15932
Organization: Queen's University
Licenced Year(s): 2016 2015
Issued: Aug 09, 2016
Project Team: Mike Palmer (Environmental Scientist, ENR-GNWT), Ryan Shaw (Field assistant, Queen's U), Noni Paulette (Field assistant, ENR-GNWT)

Objective(s): To investigate concentrations of arsenic and other elements in regional soils to gain a better understanding of regional baseline soil geochemistry.

Project Description: The specific objectives of this research are: 1) to investigate concentrations of arsenic and other elements in regional soils to gain a better understanding of regional baseline soil geochemistry; 2) to determine speciation of arsenic in selected soils from the region with elevated concentrations to determine whether arsenic in soils is from a natural geologic source or is derived from past industrial activities; and, 3) to gather detailed geochemical soil data within the YK Greenstone Belt, an area suspected to have naturally high concentrations of arsenic in soils.

This is critical pre-development information as the area is seeing renewed mineral exploration interest by several mining companies.

Pre field work planning and consultation
The research team will select approximately 200 sites within a 30 km radius of Yellowknife where soil samples will be collected over the next two field seasons. Local decision makers and the Yellowknives Dene First Nation will be consulted on sample locations. A radius of 30 km around Yellowknife is proposed because historic reports and contemporary data suggest that emissions from Giant Mine may influence locations within 15 km of the historic roasters. ArcMap GIS and pre-existing digital data layers will be used to select sites representative of regional variation in: bedrock geology, surficial geology, land cover type, soil type and saturation, distance to roaster, and direction from roaster. Since this work will complement the existing work on surface water and lake sediment chemistry in the region the research team will, where possible, attempt to couple soil sampling locations with pre-existing and planned lake sampling locations.

Collection of field data
Sites will be visited by boat, truck and foot where possible. Helicopter access will be required for more difficult to access sites. Soils will be sampled according to established protocols. Soils will be sampled with plastic trowels or corers, stored in airtight plastic bags and chilled until analysis. Water-saturated soils will be dried under nitrogen to prevent oxidation of sensitive species. Samples from the complete soil column (surface, 5 cm, 10 cm, 50 cm, base of the active layer, top of permafrost) will be collected at a smaller number of sites to investigate the geochemical profile through the soil column. Soil pore water will also be collected using suction lysimeters at sites where high concentrations of arsenic and other metals are anticipated. This is an important tool for risk assessment as it demonstrates elemental concentrations that may mobilize into soil pore water and surface water and become bioavailable during precipitation and freshet events. Field sampling protocol including site selection will build on information gained from results from previous work at the Giant Mine site.

Total elemental analysis
Soils will be analyzed by 3-acid aqua regia ICP-MS for total elemental concentrations. Results will be used to select samples for detailed speciation work, sequential extraction and leach tests and to select sites for detailed soil pore water testing based on total arsenic, antimony, gold, and copper. Results from core samples will provide information on exposure risk and potential remobilization. Results from the total elemental analysis will inform location and intervals for future sampling. Once total elemental analyses are complete for all samples collected the research team propose to apply microanalytical techniques to further investigate soil geochemistry and mineralogy. Researchers at Queen’s University have previously investigated soils within the Giant mine lease area and have expertise using microanalytical tools (Scanning Electron Microscope with automated particle characterization software, synchrotron-based X-ray absorption and micro-XRD) to investigate arsenic mineralogy and speciation. This will be critical in determining differences between anthropogenically and naturally derived arsenic. This is also an important step in identifying particle size and degree of encapsulation of arsenic-bearing particles by other minerals, as well as bioaccessibility (solubility in body fluids). For example, arsenopyrite is likely to be natural in origin and is known to have low bioaccessibility. Arsenic trioxide particles originate from stack emissions, may be ingested or inhaled by humans or animals if particles are small, and are known to be highly bioaccessible unless they are encapsulated by other phases.

An Open File is currently being drafted that summarizes all the data collected to date. Expected publication date is winter 2016. This open geoscience initiative will be particularly useful for estimation and independent review of “baseline” soil geochemistry in the Yellowknife area. Peer reviewed journal publication(s): Once data collection, analyses and interpretation are complete. Publications likely to be ready by winter 2018. A non-technical summary of the research project on completion of the project (Fall 2018).

All existing presentations and posters have been and will continue to be uploaded to the NWT Discovery Portal. Where restricted by copyright laws a record and a link to the publication will be uploaded to the NWT Discovery Portal.

The fieldwork for this study will be conducted from August 9, 2016 to October 31, 2016.