The Mine's Predictions of Particle Concentrations in Our Air

If the KGHM Ajax mine goes ahead, it will release microscopic-sized particles into the air from blasting, rock-crushing, vehicle operation, and other activities. Since airborne particles have serious health effects (see this page), it is vital to know what concentrations we could expect in the air in Kamloops. Ajax is using a computer model to calculate these concentrations. The same model is calculating how much dust is expected to fall on the ground at a number of selected locations. Ajax hired a sub-contractor, Stantec, to prepare the report on the model1 and to discuss the worst case year for emissions of airborne particles2.

In order to use the model, measurements of initial conditions must be used. Information on expected emissions from the mine site must be added to the model. Then there must be an attempt to include the physics and chemistry of atmospheric processes that will control how things change as the air moves away from the mine site. The end result is a prediction of future concentrations of particles in the air over Kamloops for periods out to the end of the projected 23-year lifetime of the mine. It is largely based on these predictions that the provincial and federal environmental assessment offices will decide whether it is safe for the people of Kamloops, and the area's ecosystems, for the mine to receive a license to operate.

The weather measurements the BC Ministry of the Environment provided to the mine were from 2003, 2004 and 2005, at various stations in the Kamloops area, but not from the proposed mine site. Ajax and Stantec decided that 2003 would be the primary year to use for the modeling and that weather data from the Kamloops airport would be the primary source. No rigorous argument was given to support why measurements from the valley bottom were applicable to what is happening 600 m (2000 ft) above at the proposed mine site. Then, using tables of standardized emission factors for contaminants, it was estimated that the highest emission rates from the mine would be in year 14, sometime around 2028, and that they would be lower in subsequent years, out to year 2037 or so. The prediction is for 25 years after the year in which the meteorological measurements were taken. Do we know what our weather and climate will be in 25 years?

The model Ajax and Stantec used is called CALPUFF. It has been used widely in modelling emissions and their evolution downwind of a source. CALPUFF was adopted by the U.S. EPA for use at distances of 50 km or more in relatively flat landscapes and for certain cases at shorter distances and in mountainous areas. Can it produce valid information over rough terrain at distances of 1 or 2 km from the proposed Ajax mine where people are living? Can it model how the topography influences the flow of air to the downtown area at the valley bottom? Is the model domain large enough to account for possible recirculation of contaminants back into the modeled receptors? Those are things that the environmental assessment will have to determine. Models do not produce data (measurements). They only produce predictions or estimates. It will be very important to clearly state the level of uncertainty that exists in the model predictions of what will be in the air we and our children will breathe.


  1. Stantec, 2013a: A detailed dispersion modelling plan for the Ajax mine project, Revised Final. Prepared for KGHM Ajax Mining Inc., 06 May 2013, by Stantec Consulting Inc., pp 58.
  2. Stantec, 2013b: Effects of the February 2013 Revised General Arrangement and Mine Plan on the KGHM Ajax Air Quality Dispersion Modelling. Letter prepared for KGHM Ajax Mining Inc., 08 May 2013, by Stantec Consulting Inc., pp 7.