Information about dust at the Giant Mine site

This information addresses topics of concern related to dust, dust management and the effects of dust at the Giant Mine site. It is not meant to replace any directives by health authorities or specific medical advice.

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Impact of dust from the Giant Mine site on residents of Yellowknife, Dettah and Ndilǫ

Recent human health and ecological risk assessments found there are no significant health risks from arsenic in dust for the surrounding communities. These studies considered recreational and traditional activities, including:

Arsenic concentrations in the air are very low. The risk assessments show that health risk from breathing arsenic in the air for residents of Yellowknife, Ndilǫ, and Dettah are negligible PDF Version (583 Kb, 2 pages).

The Giant Mine Remediation Project continually monitors air quality in the communities of Yellowknife and Ndilǫ.

Airborne dust and your health

In general, dust is present in small amounts in the air and can be made up of particles of a number of difference sizes. The largest particles are those that are more visible in the air. These particles are a nuisance but are generally not hazardous to your health.

When there is a significant amount of dust from any source, it is important to take precautions to keep from inhaling small dust particles.

Particles that can float in the air and can travel further because of their smaller size are often broken into 2 size categories: coarse and fine particles. These are the particles that are measured through the Giant Mine Remediation Project Air Quality Monitoring Program.

Coarse particles come mainly from unpaved roads, wildfires and brush or waste burning, and wind-blown soil from open areas. These particles are typically filtered out of the air as they pass through your nose. These particles may irritate the eyes, nose, and throat.

Fine particles can come from industrial activities, fuel burned to heat buildings, vehicle emissions, smoke from wildfires or form in the atmosphere because of chemical reactions of gases. These particles can trigger coughing and make it harder to breathe. They can also cause health problems or worsen conditions like asthma or other breathing issues, especially in young children and older adults.

The dust from the tailings at the Giant Mine site is non-toxic and has very low concentrations of metals. However, as with all dusts, the health hazards associated with the exposure is due to the particulate matter in your respiratory system. Particulate matter is dust that can get into a person's lungs.

Dust from the Giant Mine site near Yellowknife and Ndilǫ

Even though the project team has dust prevention measures in place at the Giant Mine site, dust can still be blown off the site on very windy days. The Giant Mine Remediation Project continually monitors air quality in the communities of Yellowknife and Ndilǫ. Air quality monitoring stations are located in Ndilǫ, the Niven Lake sub-division of downtown Yellowknife, and the marina near the Great Slave Sailing Club. Real-time air quality is measured, and filters collect the dust which is tested for metals, including arsenic.

The Government of the Northwest Territories (GNWT) also operates an air quality monitoring station in downtown Yellowknife. The monitoring from the past several years has shown activities at the Giant Mine site are not significantly affecting air quality in these communities. Please see the GNWT Air Quality Frequently Asked Questions PDF Version (583 Kb, 2 pages) for more information.

Main potential sources of dust at the Giant Mine site

Dust at the Giant Mine site mainly comes from vehicle traffic on unpaved roads and from 4 on-site tailings ponds, with a small contribution from ongoing remediation activities.

Remediation includes relocating the tailings in the South Pond to other tailings ponds. The 3 remaining tailings ponds will be drained of water, covered with a special liner made for this purpose, and topped with a clean non-vegetated rock cover. The dust from the Giant Mine site will be greatly reduced when remediation is finished. Unpaved roads not needed will be removed and traffic will be greatly reduced.

Tailings and arsenic trioxide in the tailings

Tailings are small pieces of rock and dust left over from the process of extracting gold from the bedrock. Dust from the tailing ponds contains low concentrations of arsenopyrite, which is mineralized arsenic found in bedrock.

The dust from the tailings pond does not contain arsenic trioxide, which is the more toxic form of arsenic created during the processing of ore.

Studies of the tailings ponds showed there are trace amounts of arsenic trioxide at the bottom of the ponds. These materials are buried and do not make up the dust that may blow from the surface of these ponds.

Where and how dust is monitored on site and in the communities

Dust is measured in the community, at the perimeter of the Giant Mine property, and during specific activities on site, as described below.

Community monitors
The Giant Mine Remediation Project operates 3 community air quality monitoring stations to measure dust in the air: in Ndilǫ, in the Niven Lake area, and near the Great Slave Sailing Club. The stations measure air quality continuously, year-round. Filter samples are also collected to analyze for particulates, including metals and arsenic in the air.

Site perimeter monitors
There are 9 site air quality monitoring stations near the property boundary. These provide real-time measurements of dust on site. Filter samples are also collected to analyze the dust for arsenic and other metals.

If the site perimeter or community air quality monitoring stations measure an increase in dust concentrations approaching or reaching an action level, the project team immediately investigates to find the source of dust.

Activity-specific monitors
Activity-specific air quality monitors may be used as an additional level of monitoring where remediation work, like the excavation of contaminated soils, borrow production areas, may generate larger amounts of dust or in areas of higher contamination. In addition to visual inspections, these monitors may also alert the project team to respond before any generated dust reaches the project boundary or leaves site.

Occupational monitors
Occupational monitors are also used onsite to ensure worker safety during certain work activities.

How the Giant Mine Remediation Project team minimizes dust at the site

The project team regularly monitors wind forecasts and real-time wind speed and takes measures to reduce and control the dust at site including, but not limited to:

When Giant Mine staff take action against dust

If visible dust is observed or dust is measured above an action level at an air quality monitoring station, the project team takes immediate steps to determine if the dust is related to site activities, including:

Action levels were set according to Health Canada criteria. All air criteria have safety factors built in and are set well below the level that may cause harm.

In cases where wind gusts are anticipated the project team will undertake investigation and mitigation measures prior to receiving notification from monitoring stations.

Action staff will take if dust is coming from the site

The project team will immediately assess the situation and take appropriate actions, such as:

You can find more detailed information in the Giant Mine Remediation Project Dust Management and Monitoring Plan and the Air Quality Monitoring Plan PDF Version (16,78 Mb, 132 pages) on the Mackenzie Valley Land and Water Board's public registry.

Government of the Northwest Territories and air quality advisories in Yellowknife

The GNWT's Department of Health and Social Services issues public health advisories during periods of poor air quality, like forest fires. This department is the lead on providing information on health effects related to air quality. As well, the national Air Quality Health Index is an online health risk communication tool that forecasts health risks related to air quality on a scale of 1 to 10. It gives information to area residents about protecting themselves when air quality is poor, such as during wildfire season.

Reports on project air quality monitoring

The project team sends out weekly summaries from its air quality monitoring program to the Giant Mine Remediation Project email distribution list. If you would like to be added to the project's distribution list, please email:

The weekly summary is also posted on the Mackenzie Valley Land and Water Board website.

Weekly and annual reports, as well as data, are uploaded to the territorial Air Quality Monitoring Network website.

Air quality standards used by the project to monitor dust

The project uses the Guideline for Ambient Air Quality Standards PDF Version (88,54 Kb, 5 pages) in the NWT for those contaminants that have territorial standards. For contaminants that do not have NWT standards, Ontario Ambient Air Quality Criteria PDF Version (542,64,54 Kb, 45 pages) or the Canadian Ambient Air Quality Standards PDF Version (2,73 Mb, 117 pages) are used.

The team has also established 15-minute average risk-based action levels at the site Perimeter Air Quality Monitoring Stations, incorporating Health Canada standards to protect human health for individuals both on and off the site. If a risk-based action level is exceeded at a perimeter station, the project immediately investigates the exceedance and collects and reviews data from the community stations to establish if the dust observed on site has migrated off-site.

Amount of airborne arsenic measured at the community monitoring stations

Since establishing community monitoring stations in 2013, the samples collected at the stations showed no concentrations above the ambient air quality criteria for arsenic, which is

Where the Government of the Northwest Territories monitors air quality

The GNWT monitors air quality across the Northwest Territories as part of the Canada-wide National Air Pollution Surveillance Network. The GNWT monitors air quality at monitoring stations located in 5 territorial communities, including Yellowknife. Tracking daily levels PDF Version (3,90 Mb, 4 pages) of air pollutants allows the GNWT to better assess the impacts of human activities and natural events on air quality.

How the project keeps on-site workers safe from dust

The project requires all subcontractors to have a personal Site-Specific Health and Safety Plan that addresses potential hazards on site as it relates to their work, including dust exposure. If any on-site worker is performing work in an area with arsenic exposure, they are required to undergo a medical monitoring urinalysis program, which can detect the presence of arsenic or other metals in their body.

All underground workers also follow this program. To ensure adequate dust protection for workers safety, activity specific air quality monitors or occupational monitors may be used in specific work areas if the work has the potential to generate a lot of dust.

Why the Government of the Northwest Territories recommends taking precautions around the Giant Mine site

Although dust from the site does not cause a health risk, there is still arsenic contamination in the area outside of the site from when the Giant Mine and other mines in the area were operating. Because the remediation is only occurring on the site, the arsenic contamination off-site will remain. For more information about historical mining and impacts on the area, please refer to the Where Arsenic Comes From brochure PDF Version (62,66 Mb, 2 pages).

Additional information about harvesting and hunting

Wild berries

The study of plant and berry samples completed during the GNWT human health risk assessment indicated that harvesting and consuming plants and berries from around Yellowknife, Ndilǫ and Dettah, over a resident's lifetime, is low to very low risk. The risk assessment also indicated that all the other land uses, including traditional and recreational activities, were low to very low risk. Data from the Giant Mine air monitoring program were incorporated in the risk assessment, including data from dust events. Future dust events are not expected to change the results of the risk assessments.

In order to ensure that berries and plants are safe, people should pick berries and wild plants in locations that are away from historic and current industrial activities and roadways, as per the GNWT remediation arsenic brochure recommendations PDF Version (62,66 Mb, 2 pages).


Mushrooms accumulate arsenic more easily from the environment than other plants so should not be eaten if harvested within 10 km of the Giant Mine site and Yellowknife.

Mushrooms harvested within 10 to 25 km from the site or Yellowknife pose a very low risk from arsenic exposure. However, mushrooms from the Tricholomataceae family, which includes Tricholoma, Clitocybe and White Matsutake (common names Pine and Funnel), should not be eaten if collected from within 25 km of Giant Mine site. These mushrooms tend to build up higher levels of arsenic. Please see the GNWT Frequently Asked Questions on soils, plants and mushrooms PDF Version (705,33 kb, 3 pages) for more information.

A human health and ecological risk assessment concluded that eating mushrooms harvested further than 25 km from the Giant Mine site does not pose a significant health risk from exposure to arsenic.

Some mushrooms are unsafe to eat (toxic) for reasons other than arsenic, such as mushrooms that are naturally poisonous. Mushrooms should only be harvested by or with someone who is experienced in identifying them properly.


The GNWT's risk assessment showed there is a very low risk from eating large and small mammals from around the Yellowknife area, such as:

  • moose
  • rabbits
  • muskrat
  • beaver
  • land birds such as grouse or ptarmigan
  • waterfowl

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