Engineering firm CH2M HILL released the report The Changing Value of Water to the U.S. Economy: Implications from Five Industrial Sectors in 2012, compiled for the U.S. Environmental Protection Agency as part of its initiative titled “The Importance of Water to the United States Economy.” The report, authored by Mike Matichich, Marek Mierzejewski, Bill Byers, Dan Pitzler and Sartaz Ahmed of CH2M HILL, examines the critical role water plays in industrial production and how the value of water is changing in certain major industrial sectors. The information pertaining to the mining industry is excerpted here.
Mining companies in the United States, and globally, are exploring proactive approaches to water that consider how to demonstrate the value of water, taking into account not only economics, but also considering social and environmental factors as well.
At many sites, the operations make use of non-potable water, thereby avoiding the use of high-quality (potable) water and helping to conserve local water supplies. Although the minerals and metals industry is a small user of water on a national scale, it can be a large user at a local level. Some sites are located in water-scarce locations where mining companies compete with other water users, including local communities, agriculture and other industries, while in some locations companies need to manage significant water flows resulting from precipitation or groundwater sources. Many mining operations recycle significant amounts of water onsite, and water management, discharge, and use are subject to comprehensive regulatory and legal requirements.
Rio Tinto adopted a water strategy that provides a framework for managing water and improving business performance across the social, environmental, and economic aspects of water management. The strategy has three main components: improving performance, accounting for the value of water, and engaging with others on sustainable water management. A key focus is to identify ways to minimize the amount of water removed from the environment, reusing it when possible, and returning it to the environment while meeting, at a minimum, regulatory limits.
Rio Tinto has decided to invest in water conservation (for example, by making processes more efficient or using poorer-quality water in place of potable water) because it understands the value of water. The company looks beyond the cost of water to take into account nonmonetary aspects such as social and environmental values. Rio Tinto has observed that perceptions of value may also change; for example, communities, governments and business place great importance on water conservation during droughts. This concern often quickly diminishes when the drought ends. A longer-term approach that takes the full value of water into account would support decision-making on sustainable water use. While these approaches are still being developed and tested, two of Rio Tinto’s companies are taking creative approaches to valuing water.
Rio Tinto’s Kennecott Utah Copper operations are located near Salt Lake City, Utah, where its business has been operating for 110 years. Increasing population and other factors are placing more pressure on water resources within the region, making sustainable water management critical to Kennecott. Greater than 90% of the water used at Kennecott is characterized as poor-(low) quality water, and an average of 60% of the water withdrawn is recycled to minimize importing additional water resources.
The largest water user at Kennecott is the concentrator. However, more than 90% of the water used at that concentrator is from recycling. To drive water performance improvements, Kennecott is developing a water management approach that recognizes that different waters have varied benefits and costs that support using different waters for different purposes. This water hierarchy approach recognizes the need to balance a number of considerations including availability of water and water quality; the location and type of infrastructure required to transport or treat water; energy use; and regulatory or legal requirements. Kennecott’s water hierarchy approach aims to do the following:
- Use poorer-quality water first in operations to minimize the amount of new, clean water required for use.
- Recycle process water where practicable.
- Separate waters of different quality to optimize water use within the process. Maintain direct involvement and support with the scientific community in advancing technologies and education in improving best practices and methodologies.
- Educate the workforce in best water management practices.
For example, when a groundwater source used by the concentrator became unavailable, Kennecott applied the water hierarchy approach to select a replacement source. Kennecott assessed several possible alternative sources, including: potable quality groundwater; surface water suitable for irrigation, and recycled water sources from its operation. The three replacement sources each carried distinct costs and benefits. No source was adjacent to the concentrator, so each source carried transportation infrastructure and operational costs, which differed according to relative proximity. Although recycling required transportation across 13 miles compared to 3 miles for potable groundwater, existing infrastructure was available for recycling. The need for new infrastructure for the groundwater and surface water sources increased the “costs” of these water sources. Additionally, using recycled water preserved potable groundwater to meet existing and future culinary purposes and saved the surface water for agricultural use. Capital and operational costs, however, were not the only considerations. Poor water quality can impact metals recovery during the milling process; therefore process changes were also needed to limit inhibited metal recovery. Kennecott ultimately replaced the original groundwater source with the lower quality recycled water. The decision considered tradeoffs among operational needs, energy requirements, new infrastructure, and the economics of each option. However, the water hierarchy approach was the primary guide that led to the decision to use the recycled water source.
The Resolution Copper project is located near Superior, Arizona. The large world-class copper resource lies one or more miles below the surface where a previous mine had been developed and later closed in the mid-1990s. A proposed underground mine is projected to produce more than 1 billion lb of copper per year over approximately 34 years. A 2011 economic and fiscal impact study estimated that the total economic impact of the Resolution project on the state of Arizona will be over $61.4 billion.
To begin developing the new mine, more than 2 billion gallons of water that naturally accumulated in the old mine had to be removed. Resolution constructed a $20-million water treatment facility to prepare the water for discharge once it is pumped to the surface. Initial draining of the old mine took nearly three years to complete. One of the challenges was determining where the removed groundwater should go once treated, to ensure the water is fully used and the environment is not negatively affected.
Resolution worked with the New Magma Irrigation and Drainage District (NMIDD) to supply the extracted water for agricultural use in Arizona. The project involved constructing a 44-km pipeline to transport the water from Resolution’s treatment facility in Superior to Magma Junction. NMIDD will combine this water with Central Arizona Project (CAP) water for irrigation purposes. CAP delivers water from the Colorado River by canal to central and southern Arizona so surface water can be used instead of depleting groundwater for agricultural, municipal, and industrial uses.
In parallel with draining the old mine, Resolution has had to plan for operational needs of up to 20,000 acre feet (approximately 6.5 billion gallons) per year, principally for the flotation process used to separate the valuable ore from the waste minerals. While groundwater is the most readily available and least expensive water source for the mine, the company sought alternative, more sustainable resources. In total, Resolution identified 25 potential sources and ranked them according to social, environmental, and economic criteria.
Resolution identified three sources as future supply options for water:
- Groundwater that was previously affected by mining: this would only satisfy about 10% to 20% of the new mine’s ultimate need.
- Banked water with the CAP: Resolution is purchasing and “banking” excess CAP water with the irrigation districts for future use, minimizing its impact on water supply.
- Treated municipal wastewater effluent: Resolution is working with the Science Foundation Arizona, the University of Arizona an Freeport-McMoRan on technology to use treated municipal effluent in the flotation process, thereby lessening demand on other sources, such as groundwater.
