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Investigation of Aquatic Impacts of On-Ice Exploratory Diamond Drilling

Organization / Researcher: Anne Wilson

Length of Project: 3 years (1997-2000)

Personnel involved: At least 10 including technicians and students, lab assistants, scientific advisors, and staff at Environment Canada,
Department of Fisheries and Oceans, DIAND's Mineral Development Division, Diavik and Royal Oak mines and their drilling contractors.

Total Project Expenditures: $28,272

This project looked at the effects of diamond drilling through the ice on water quality, sediment quality and lake bottom organisms. This information is needed by both industry and regulating agencies responsible for granting mineral exploration permits or water licenses. Short drilling holes, like those examined, are typical of first stage mineral exploration drilling; the results are relevant to much of the drilling activity in the Slave Geological Province.

Parameters measured included water cloudiness caused when diamond drilling disturbs lake bottom sediments and releases rock particles into the water, and the thickness of material deposited. Sediment samples were analyzed for changes in sediment chemistry and particle size. Lake bottom organisms were identified and counted before and after drilling.

The study examined three drilling sites. Two of the sites were non-kimberlite: Baton Lake (near Colomac Mine), and Great Slave Lake in Yellowknife Bay near Yellowknife. Lac de Gras (Diavik Diamond Mines) was a kimberlite drilling site, and had different results.

At Baton Lake, approximately one cubic metre of rock fines were released (a typical amount for normal exploratory drilling) forming a layer up to 7mm thick at the discharge point. Sampling one year after drilling waste release showed that the fines layer had been covered with a 10-20mm layer of organic materials which had been recolonized by bottom organisms; there was no significant change in numbers of individuals for the two major taxa (groups or families of animals), though the number of taxa at each hole decreased from four to an average of 2.4. Sediment chemistry showed a slight but not significant increase in aluminum and magnesium after drilling. Water quality measurements were the same as before drilling.

Great Slave Lake drilling had little effect on water quality; all measurements were the same as before drilling took place. Sediments settled to the bottom quickly, forming a thin coating of less than 1mm in the area of effluent discharge. There were significantly fewer bottom dwelling organisms at the drilling discharge point but no significant difference 15 metres away, indicating that impacts were localized.

Findings at Lac de Gras were somewhat different, as drilling through kimberlite produced a more toxic effluent. Effluent chemistry at Lac de Gras showed levels of aluminum and magnesium high enough to be toxic to fish (at the time of drilling). There was a significant drop in numbers of bottom organisms shortly after drilling but numbers had recovered a year later: the number of taxa actually increased, possibly because of a boost in micronutrients resulting from the deposition of sediments.

In a laboratory experiment involving aquaria, organisms from Great Slave Lake were covered with 1, 3, and 7mm layers of drilling wastes, as would happen during drilling. Impacts were not significant. Only a few organisms died; most remained in their own layer, or constructed new burrows.

The study concluded that release of drilling effluent produces temporary and localized effects. For shallow, non-kimberlite drilling targets, diamond drilling through ice does not cause extensive physical or chemical disruption; there was no significant addition of toxic material to the lake bottom, and no significant effect on bottom dwelling organisms. However, the researcher recommended that release of kimberlite-associated drilling effluent not be permitted unless prior testing establishes that the effluent is not toxic to fish.