NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: contaminants, arsenic, soil chemistry

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. Activity 1: 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 15km of the historic roasters. ArcMap Global Information System software 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 team’s 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. Activity 2: 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 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, including two MSc theses at Queen’s, and recent collaborations with Golder Associates. Activity 3: Total elemental analysis Soils will be analyzed 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 in the soil column. 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 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. Selected samples will be tested by carefully-designed sequential extraction and leach extractions to determine if relatively simple tests could be used as a proxy for detailed mineralogy to identify soil samples that represent higher risk. The Yellowknives Dene First Nation (YKDFN) were consulted during the drafting of the research proposal and have offered their support of the proposed project. The YKDFN have long had concerns regarding legacy contamination from past mining activities in the region that extend beyond mine lease boundaries and consequently beyond the mandate of the parties that are responsible for those sites. Undertaking a regional soil geochemical sampling program will provide important information to the YKDFN on how areas that may be used by local land-users have been impacted by legacy activities. There has also been a long standing concern that soils within Ndilo and Dettah may have been impacted by historic roaster emissions. The project team will collaborate with the YKDFN to collect information from Ndilo, Dettah, and the Dettah Road area that will complement previous work that has been undertaken in the area to provide a better sense of risk to the health of YKDFN members. Staff at the Lands and Environment Office will be kept up to date on research results through local project team members. Annual meetings with interested YKDFN members will be arranged through YKDFN staff. Meetings: As some of the project partners are located in Yellowknife, there will be multiple opportunities to meet with local decision makers, industry, and aboriginal organizations. Examples of specific meetings include: •Solicit feedback on study design and proposed sample locations from local decision makers (ie. Land and Water Boards, Government of the Northwest Territories, Giant Mine Remediation Team), industry (TerraX), YKDFN, and North Slave Metis Alliance. •Sharing of preliminary results with stakeholders during week of the Yellowknife Geoscience Forum. From past experience, the project team has learned that this an effective time to communicate results, as several project partners will likely be in Yellowknife during the Forum and will allow for face to face communication with project experts. •Additional meetings as needed. Local project team members will keep in contact with local organizations throughout the year and will be available to meet when new information becomes available. Presentations: •Yellowknife Geoscience Forum: presentation of preliminary results. •National and International conferences: once project has clear findings that are of interest to the wider scientific community. •Expect 1 or 2 presentations each year to local communities, decision makers and national/international science community. Publications: •Joint Geological Survey of Canada-Northwest Territories Geoscience Office (GSC-NTGO) Open File(s): once all field data has been collected and total elemental analysis is complete data will be compiled and described in a joint GSC-NTGO Open File for public access. 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. •A non-technical summary of the research project on completion of the project. •Annual year-end reports as per Cumulative Impacts Monitoring Program funding agreement. •All publications will be uploaded to the Northwest Territories Discovery Portal. Where restricted by copyright laws a record and a link to the publication will be uploaded. The fieldwork for this study will be conducted from July 16, 2015 to November 1, 2015.