Mining activities involve potential sources for fugitive emissions and hot vapors from smelting operations that may contain toxic levels of metal and metalloids. Mechanical action activities such as grinding and crushing of the ore are associated to emissions of coarse particles that can deposit in the lung airways. Fine particles, which are related to high temperature processes can penetrate deep into the lungs and can even migrate to other organs. Arid regions such as Arizona are susceptible to dust storms and metal and metalloids contained in the dust can travel long distances and deposit in vegetated areas, soil and water. The mining facility of this study, the ASARCO-Hayden Plant, located in the twin cities of Hayden and Winkelman in Arizona, is a major producer of copper and other metals. There is evidence that their activities represent a threat to the residents and environment. For example, the US EPA estimated that the lifetime cancer risk of the people living in Hayden and Winkelman is as high as one in one hundred.
Dust emissions from mining operations and dispersion of contaminants can be investigated by means of field measurements and through computer modeling. Concentrations of toxic metals and metalloids such as As, Cd, and Pb where obtained from a multiple orifice uniform deposit impactor (MOUDI) for 10 cut-point aerodynamic diameters. Results show that concentrations follow a bimodal distribution with means around 0.3 and 7 μm. It is hypothesized that the fine size range (<1 μm) fractions are the product of condensation and coagulation of smelting vapors and that the coarse size range (3-18 μm) are part of dust generated from mine tailings and fugitive emissions from mechanical action activities.
Emissions from the hypothesized sources are simulated using Calpuff® and Fluent® for validation purposes. Calpuff results show little agreement to measured concentrations when a flat terrain and constant emissions were incorporated in the model. Current work involves modeling aerosols emissions using computational fluid dynamics with models that incorporate an Eulerian approach. Real meteorological data and topographical features are planned to be included in the simulations.