Sherritt International has completed a second series of tests of soil and sediment, which are deposited solids, on the Obed Mountain Mine site and surrounding environment. This represents the next phase of environmental work aimed at determining the potential impacts of the water release from a mine site pond on October 31, 2013. The results of these soil and deposited solids tests generally indicate that the levels of constituents were below federal and provincial environmental guidelines. There were a minority of sample results that exceeded the guidelines; however, the level and nature of those exceedances appear to indicate that these are likely due to a variety of natural environmental causes that are unrelated to the mine operations or may, in part, be related to the mine operations. Additional studies are underway to advance the understanding of the causes of these exceedances. It is important to understand the guideline values are published to encourage further investigation to determine if potential risk to the environment or human health exists.
Preliminary assessment of the data suggests that the number and magnitude of exceedances are not considered a risk to the water in the nearby creeks or the Athabasca River. Sherritt is taking measures to ensure these soils and deposited solids are stable, contained and prevented from moving into any water course during the spring melt.
As was previously reported, immediately after the water release there were temporary and short-term exceedances of water quality guidelines in the area creeks and Athabasca River. However, ongoing water tests have shown that there are no longer any exceedances of the water quality guidelines, indicating that the water is safe for humans, wildlife, fish, and the food chain that supports fish.
During this second series of soil and deposited solids tests, 200 samples were collected from 138 unique sample locations on the mine site, along and outside of the water spill path, and along the first 5 kilometres of Apetowun Creek.
The samples were collected in three rounds of sampling on the following dates: November 8-9, 2013, January 8-11, 2014 and January 29-30, 2014.
The chemical analysis data have been, and will continue to be, compared to Canadian Council of Ministers of the Environment (CCME) water and sediment quality guidelines and to the Alberta Tier 1 Guidelines. The CCME and Tier 1 guidelines provide information on what chemical parameters may be of concern and at what concentrations present a potential for environmental risk.
The soil and deposited solids chemistry data are compared to two guidelines established by the CCME which provide the following information:
- Interim Sediment Quality Guidelines (ISQGs) – if chemical concentrations are below the ISQGs they are not of concern, if they are above they may or may not be of concern; and,
- Probable Effect Levels (PELs), which are higher levels than the ISQGs – if chemical concentrations are below the PELs they may or may not be of concern, if they are above they are likely, but not certainly, of concern.
Key findings are as follows related to the substances whose concentrations exceeded their CCME Probable Effect Levels:
- Arsenic and selenium exceeded the respective PELs; however, the geographic locations of these exceedances are contained in a very small area and were found in the in situ, or natural, soil. This would indicate that these parameters existed prior to the release and therefore are unlikely to be related to the event.
- Of the polyaromatic hydrocarbons (PAHs), only 2-methylnaphthalene was detected in concentrations likely of concern; there were no other PAHs that exceeded the PEL.
- Molybdenum is also of potential concern. There are no CCME sediment quality guidelines for this metal; however, there were exceedances of the Alberta Tier 1 soil guidelines.
As noted above in the key findings, in one small isolated area, very high concentrations of arsenic and iron, as well as elevated concentrations of molybdenum and zinc were found. These high concentrations are an anomaly that appears to be naturally occurring likely as a result of groundwater discharge to surface. This area has not been disturbed by mine operations and is not in the water release path, suggesting it is a natural geological event that is not related to the water release or the operations of the mine. One result showed the soil composition was 41 percent iron, which is certainly unusual. The Geologic Survey of Canada states that natural seeps do occur in the area. Further investigations into this seep to confirm that it is a natural geological event are on-going.
The results of these tests, and maps of the corresponding sample locations, are posted in the tables on this page.
Further investigations are on-going, particularly into the above-noted substances of likely concern, to determine whether they pose a risk to organisms living on or in the sediments. Ongoing removal of the deposited solids is continuing.