Mine water stewardship in Arizona

The Colorado River. Image from Shutterstock. On May 6, 2022, the Central Arizona Project and the Arizona Department of Water Resources (ADWR) held a public briefing on Colorado River Shortage Preparedness. The briefing started with three observations. First, the Colorado River Basin drought has lasted more than 22 years. Second, dry soil, higher temperatures, and low precipitation represent the driest basin conditions in more than 1,200 years. Third, the Colorado River was 36 percent of Arizona’s water supply in 2020. The briefing ended with the certainty of further reductions to Arizona’s Colorado River allocation in 2023 — beyond the 30 percent reduction instituted in January 2022. One full year later, the states of Arizona, California and Nevada (lower division states) agreed to conserve an additional 3 million acrefeet (MAF) of Colorado River water by the end of 2026. This agreement followed the February 2023 release of the Near-Term Colorado River Operations Draft Supplemental Environmental Impact Statement, prepared by the Bureau of Reclamation. As proposed in the agreement, up to 2.3 MAF of compensation will be federally compensated under the Inflation Reduction Act. The remainder “may be in whole or in part compensated (or be uncompensated) by state and/or local entities.” The complexity of the Colorado River legal framework and the reality of the current basin condition triggers a statewide ripple effect in terms of water supply planning and allocation in Arizona. In 2021, Arizona copper mining (for example, metal mining) accounted for 74 percent of the domestic U.S. copper production (U.S. Geological Survey, 2021). At least two Arizona copper operations import Colorado River water as a portion of freshwater supply. How do the major copper producers in Arizona navigate the sustained drought conditions, climate change forecasts and complex legal frameworks of today? The solutions lie in a collaborative strategy involving long-term conservation planning and a sustained commitment to water stewardship. Regulatory brief The most recent statewide water conservation measures announced in 2022 and 2023 are the latest of a long series of forwardlooking water strategies in Arizona, accelerated by the construction start of the Central Arizona Project in 1973. Established in 1980, ADWR assumed responsibility for all groundwater planning and regulation in the state except for water quality. This legal authority included development and oversight of mandatory conservation programs for groundwater use in four areas of heaviest groundwater pumping, classified as active management areas (AMAs). ADWR’s legal authority on groundwater use outside of the AMAs requires users demonstrate a reasonable and beneficial use. In this role, ADWR regulates “groundwater mining.” The act includes the provision that developers of new subdivisions within AMAs demonstrate a 100-year assured water supply. ADWR monitors and models groundwater use within each AMA. On Jan. 9, 2023, Arizona Gov. Katie Hobbs announced the ADWR cannot approve the development of subdivisions reliant on groundwater in the Phoenix AMA. This announcement was based on the ADWR finding that Phoenix’s West Valley is short of its 100-year supply of water. The Surface Water Division of ADWR administers permits, certificates of water rights and claims to the appropriation of surface water in the state. This legal authority defines beneficial use as the basis, measure and limit to the use of surface water. Mining is one beneficial use. Established in 1987, the Arizona Department of Environmental Quality (ADEQ) assumed responsibility for surface and groundwater quality protection through various water quality programs. The aquifer protection permit requires compliance with aquifer water quality standards at the point of compliance, and operators to demonstrate best available demonstrated control technology (BADCT). The purpose of BADCT is to employ engineering controls, processes, operating methods or other alternatives to reduce the discharge of pollutants to groundwater to the greatest degree achievable. ADWR provides specific conservation requirements for metal mining facilities in AMAs. The Fifth Management Plan (2020), published for the Tucson AMA, defined a series of water conservation-related best management practices (BMPs) for metal mining facilities. These BMPs are generally consistent with BADCT guidelines under the ADEQ aquifer protection permit program. There are multiple water-focused public agencies, private utilities and councils involved in conservation, storage and strategic resource planning in Arizona. In terms of water stewardship and metal mining, ADWR and ADEQ are the primary agencies of interest for this article. Metal-mining water consumption estimates ADWR (2020) estimates industrial use accounts for 6 percent of water consumption in Arizona. Metal mining (that is, mining operations that consume more than 500 acre-feet per year) is one of several industrial uses, in addition to turf-related facilities, sand and gravel, and largescale power plants (greater than 25 MW). At the statewide scale, metal mining consumption is about four times less than municipal use (22 percent) and at least 10 times less than agricultural use (72 percent). ADWR manages six AMAs: Prescott, Phoenix, Pinal, Tucson, Santa Cruz and Douglas. Metal mining occurs in the Phoenix (one facility), Pinal (one facility) and Tucson (six facilities) AMAs. ADWR estimates metal mining in 2020 accounted for 39 percent (approximately 432,000 acre-feet) of AMA total groundwater use (eight facilities within the Phoenix, Pinal and Tucson AMAs). This is a partial accounting because groundwater is one of several classified water resources and metal mining also occurs outside of designated AMA boundaries. The relevant context of water use by metal mining operations is basin specific. Water consumption at a large metal mine depends on the volume of ore mined, commodity, mineral processing methods, and availability and type of water resources. Industry best practice Water stewardship includes evaluating water supply and water quality impacts associated with mine operations, closure and postclosure. Best practice extends this analysis on a basin-wide basis with active collaboration toward use that is socially equitable, environmentally sustainable and economically beneficial. This aspect of water stewardship is an imperative for metal mine operations in the arid, semidesert climate of Arizona. Evaporation and entrainment (for example, water retained within conventional tailings storage facilities and leach stockpiles) account for a significant portion of water consumption. Large-scale metal mine operations have worked to maximize water use efficiency and promote use of recycled, reused and lower-quality resources for decades. Examples of best practices in Arizona include: Minimizing use of freshwater and impacts to freshwater quality. Modeling and planning for climaterelated impacts in terms of engineering and promoting water-supply resilience.Continuing improvement in terms of maximizing recycled/reused water.Investing in research and field demonstrations of new technologies designed to reduce water consumption.Collaborating with other actors in the management of the water basins to manage and develop water resources in a sustainable and balanced manner, considering the social, economic and environmental interests of the actors. The emergence of responsible production initiatives for global mining activities represents new drivers promoting water stewardship. Other trends include early experimentation with integrating natural capital (for example, water value) into business decision-making. These water-related goals and metrics by established operators align with the long-term conservation planning required for metal mines by ADWR as well as the updated drought mitigation measures issued by ADWR and the Central Arizona Project. Plans for new metal mines include adoption of emerging technologies such as filtered tailings, reduced evaporation from water storage facilities, less water-intensive dust control, and increased water reuse overall. These plans, combined with adaptive management and stakeholder engagement, will guide metal miners through this complex landscape. Saguenay-Lac- Saint-Jean in Canada, where a state-of-the-art aluminum smelter complex is being expanded with low-carbon technology. (Image from Rio Tinto.) Rio Tinto will invest $1.1 billion (C$1.4 billion) to expand its state-of-the-art AP60 aluminum smelter equipped with low-carbon technology at Complexe Jonquière in Canada, Business Wire reported. The total investment includes up to $113 million (C$150 million) of financial support from the Quebec government. The expansion, which will coincide with the gradual closure of potrooms at the Arvida smelter on the same site, will enable Rio Tinto to continue meeting customers’ demand for low-carbon, high-quality aluminum for use in transportation, construction, electrical and consumer goods. The investment will add 96 new AP60 pots, increasing capacity by approximately 160 kt/a (176,000 stpy) of primary aluminum, enough for 400,000 electric cars. As a result, there will be a total of 134 AP60 pots and a capacity of approximately 220 kt/a (242,000 stpy). Construction will occur over two and a half years with commissioning of the new pots expected to start in the first half of 2026 and the smelter fully ramped up by the end of 2026. Once completed, the expanded smelter is expected to be in the first quartile of the industry cost curve. This new capacity will offset the 170 kt (187,000 st) of capacity lost through the gradual closure of potrooms at the Arvida smelter from 2024. In addition, Rio Tinto will add 30 kt (33,000 st) of new capacity through the commissioning of the previously announced recycling facility at Arvida in the first quarter of 2025. The AP60 smelting technology was developed by Rio Tinto’s research and development teams and is among the most efficient and lowest carbon technology currently available at a commercial scale. When combined with the hydropower used at Rio Tinto’s operations in Canada, it generates one-seventh of greenhouse gases per tonne of aluminum when compared with the industry average, and half the emissions when compared to the technology currently used at the Arvida smelter. The project will generate up to 1,000 jobs during the peak of construction and approximately 100 permanent jobs will be maintained as a result of the expanded smelter. Rio Tinto chief executive Jakob Stausholm said: “This investment is aligned with our strategy to decarbonize our value chains and grow in materials essential for the energy transition. Our AP60 technology is already proven and producing some of the lowest-carbon aluminum in the world, thanks to the expertise of our highly qualified workforce and access to renewable hydropower. This is the most significant investment in our aluminum business for more than a decade and it will further strengthen Rio Tinto’s high-quality and low-carbon offering to our customers as they also work to reduce their own carbon footprint.” Quebec Premier François Legault said: “A great momentum is building in our regions for our green economy. The aluminum industry in Saguenay-Lac-Saint-Jean has always been a real source of pride and has created considerable wealth in the region. Today’s announcement will breathe new life into this industry with greener, less polluting processes.” Rio Tinto and the Canadian government have also signed a memorandum of understanding that deepens their commitment to strengthen supply chains for low-carbon primary metals, critical minerals and other value-added products. The cooperation will also aim to support projects that have the potential to grow Rio Tinto’s activities in Canada, including the current and future decarbonization of the aluminum supply chain.

Mine water stewardship in Arizona

Authored by:
Terry Braun

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To view the past issues of the UCA magazine you must be a member of SME/UCA.

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