The Mt. Polley Mine disaster highlights the risks involved with the proposed Ajax tailings storage "pond" or reservoir. This reservoir will be 6 km², three times the size of the Mt. Polley reservoir. It will be situated at the headwaters of Peterson Creek.. A major failure of one of the dams on this reservoir could cause a catastrophic flood of tailings sludge through Peterson Creek and into downtown Kamloops and the Thompson River, or west through Cherry Creek and into Kamloops Lake. As the reservoir grows, there will be beaches surrounding the reservoir as water levels fluctuate. These will be a major source of toxic dust which will be carried by prevailing winds over Kamloops Valley.
Here are some of the dimensions of the proposed tailings facility and South Waste Rock Facility.
The tailings impoundment will have a maximum elevation of about 1,065 metres above sea level (masl) on the west side. The lowest spot around the perimeter of this impoundment is about 887 masl. This suggests a maximum height from this low spot to the top of the tailings embankment of 178 metres (584 feet). There is only one taller building in Vancouver, the Shangri-La at 201 metres. At this point, the impoundment, will consist of considerable waste rock, up to 1,000 metres in width, but built on an underlying slope averaging about 9%.
Natural terrain will form part of the tailings perimeter. However, 4 separate sections of embankments will be constructed, including the highest section mentioned in the previous paragraph.
On the west side, there will be no waste rock buttressing the tailings embankment. The lowest spot on this section is approximately 972 masl, suggesting a maximum embankment height of 93 metres.
Two other, shorter sections, on the south perimeter will be much smaller in height. Given that the terrain slopes higher to the south, it is a question as to why embankments are even needed on this side.
The height of the largest waste rock facility, the South Waste Rock Facility, will have a final elevation of 1,135 masl. On the north east side of this rock dump, where there is a fairly uniform slope to Peterson Creek, the base of this facility is about 1,000 masl - hence a waste rock height of about 135 metres at this point. At this point the creek is about 1,000 metres away, and the elevation of the creek is about 870 masl. This is an elevation change of 130 metres over 1,000 metres for an average slope of 13%. Maintaining stability of this waste rock dump, and the other dumps, must be done in perpetuity, as any significant failure could affect Peterson Creek, and possibly cause a debris flow.