Update on soil studies in Ndılǫ, Northwest Territories

Since 2001, the soil in and around Ndılǫ has been sampled for arsenic many times to address community concerns about contamination from the former Giant Mine.

Two samples taken as part of a study in 2012 raised further concern because they showed higher levels of arsenic than similar samples collected in 2001.

Experts concluded more research was needed. This included:

The Yellowknives Dene First Nation commissioned the studies, and Crown-Indigenous Relations and Northern Affairs Canada funded them.

The Yellowknives Dene First Nation hired Det'on Cho Environmental to do the 2018 study and analysis. Det'on Cho partnered with Hemmera Envirochem Inc. to conduct the sampling program and analysis. They provided a 2018 Ndılǫ Soil Report in September.

As part of the 2018 study, the consultants collected soil samples at surface and below ground surface from the area that showed elevated arsenic levels in 2012. They collected additional soil samples to help determine the size of the pocket of elevated arsenic. Also collected were other samples around a playground because the community identified it as an area of concern.

The 2018 study concluded:

The 2018 samples taken in the areas of concern, as identified by the Yellowknives Dene First Nation, ranged from 19.0 mg/kg to 64.2 mg/kg.

The consultants recommend that no further action is needed.

In their analysis, Det'on Cho Environmental suggests that the two elevated levels found in 2012 were outliers. Multiple samples have been taken in those locations since 2012, and none have reproduced the results found by that study.

The consultants conclude this may have been the result of the "nugget effect". The "nugget effect" happens when metals being measured are very tightly clustered in one spot (nugget): finding the nugget in a representative sample can mean the levels are overestimated.

In addition, since the sample measured in 2012, a number of natural processes occurred, such as rainfall and soil disruption, possibly leading to the disturbance of the arsenic. This may be why samples have not shown the elevated level since that time.

It is important to note that, even when the 2012 soil study results were factored in, the Human Health and Ecological Risk Assessment completed for the Giant Mine Remediation Project concluded risks to human health from arsenic in soil in Ndılǫ were low.

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