Air Quality and Climate Change

Corresponding pages in the DEIS:
Summary of Impacts: pp. 158-205; Environmental Consequences: pp. 177-205

Under the proposed action, particulate matter 2.5 (PM2.5) would increase by two times versus background levels, and particulate matter 10 (PM10) would increase by more than three times versus background levels. National Ambient Air Quality Standards for particulates would not be exceeded, but those for PM10 would be close to exceedance (97 percent of standard). Volatile organic compound emissions would be about 105 tons per year and would represent less than a 1 percent increase in Pima County. Nitrogen oxide emissions would be about 1,250 tons per year and would represent a 4 percent increase in Pima County; this would increase the risk of an exceedance of the ozone air quality standard in the Tucson area. Sulfur dioxide emissions would meet the air quality standard at the project site. Greenhouse gas emissions (carbon dioxide) would represent a 1 percent increase in Pima County. Emissions from the project would cause and contribute to degradation of visibility in the Saguaro Park East and Galiuro Wilderness Class I airsheds.

Rosemont Copper has committed to using numerous mitigation measures to minimize emissions and their impacts. These include: operational and engineering controls for controlling fugitive dust associated with the tailings, water sprays and wet scrubbers associated with the ore crushing; use of covers to control emissions from mix tanks and settlers used in the solvent extraction system; spray or physical enclosures for low emission potential processes; location of stockpile and loadout areas within the enclosed stockpile building; use of newer engine designs in mobile sources, dust control on access, haul, service, and maintenance roads; use of low-sulfur diesel fuel onsite for all stationary equipment; expedited construction of electrical lines to reduce the need for onsite power generation and associated emissions; design of the project administration building to showcase use of leadership in environmental and energy design and sustainable energy concepts; and application of acid leaching solution to the heap using emitters (similar to drip irrigation) to avoid aerosol losses to the wind.

Impacts to Air Quality

The area currently has excellent air quality. Tailings and waste piles will be sources of dust, which prevailing winds will blow toward residential areas. Air quality in the National Forest and surrounding residential areas will be degraded by both dust and truck exhaust associated with mine operations.

As a case-study, consider the problems Pima County has seen with the Asarco mine in Green Valley: http://www.gvnews.com/articles/2010/01/21/news/59county%20dust%200110.txt