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On a 107 degree morning in the mountains east of Phoenix, a miner in a hard hat plunges down the nearly 7,000-foot shaft of what may soon be the biggest underground copper mine in the United States.

But for now, the Resolution Copper mine isn't taking out copper. It's taking out groundwater, at a rate of around 600 gallons per minute. Because this copper is so deep underground, in geologic formations dating back more than a billion years, the mining takes place far below the water table. The mine is removing that aquifer water so the operations don't flood. And the mine is giving away this water for free to nearby farmers, about 6 billion gallons so far.

This summer, Arizona state officials declared they won't permit some new home construction in the 

 because of concerns about groundwater. The region's groundwater supplies are under increasing stress from drought and climate change. But it's in that same Phoenix metro region where Resolution plans to remove groundwater for its mining operations. If the mine gets its environmental permits and begins full operations, Resolution would use billions of gallons of local groundwater and stored Colorado River water for the next 40 years.

The U.S. is pushing to secure new domestic mining supplies for metals such as copper, lithium and manganese that are critical for building things like electric vehicle batteries, solar panels and other components of the energy transition away from fossil fuels. But much of the exploration and planned production of these minerals is taking place in the arid American West, where water is increasingly scarce.

Mines like Resolution say they are using new technologies to extract and process minerals with less water. But researchers and Indigenous groups worry about the impacts of drawing down local aquifers as part of mining and the impacts on local water quality. Critics say that the Arizona mining sector's water usage is too lightly regulated and that much of the data on water usage is self-reported by companies.

Today, with the intertwining crises of climate change and declining water supplies, the drive to unearth the West's energy transition minerals is colliding with the need to protect the water that remains, says 

, a law professor at Washburn University School of Law who researches Western water law. "The major challenge that we're facing in the West regarding these critical minerals is," Griggs says, "is there water available to make the mining of these critical minerals feasible?"

"The stakes could not be higher, because once groundwater is gone," he says, "that groundwater is not going to be coming back anytime soon."

Green tech mining brings up concerns about water scarcity and quality

Water is an important part of mining, as companies use it to process metals and for various forms of dust control. When working deep underground, mining companies often remove aquifer water so it doesn't flood their mines. And producing lithium through large evaporation ponds can be particularly water intensive.

Many Western states with dwindling aquifers are seeing massive investments in new mines to supply the green tech industry. Arizona, California, Nevada and Utah are exploring and developing new lithium projects. Arizona and Utah are investing in new copper projects, and the 

 for a new manganese and zinc project south of Tucson, Arizona.

These metals are key for climate solutions. Lithium and manganese are used in electric vehicle batteries and batteries that store renewable energy. Copper is used in electric vehicles, and both copper and its mining co-product, tellurium, are used in solar panels and other green technologies.

As the transition away from fossil fuels gains momentum, demand for these minerals could outstrip supply. The world will need 50% more than current supplies of copper to meet projected demand by 2030, according to the Net Zero by 2050 scenario from the 

. By 2030, projected lithium demand will be five times the current global supply, according to the International Energy Agency. Domestic supplies of manganese could also be a challenge if the U.S. doesn't invest in local mines or processing plants, says Susan Zou, vice president at Rystad Energy, a research company.

Resolution could produce a quarter of current U.S. copper, and it could double the U.S. tellurium supply, says Vicky Peacey, president of Resolution Copper, a joint venture of mining giants 

. "Deposits like what we have," she says, "help fill that gap, but it needs to be done differently, right? We are underground. We will use less water. Obviously, there's a path to electrification, and we need to do it in a way that society demands of us."

Resolution's treated excavated aquifer water currently goes to farmers who use it mostly to grow alfalfa for dairy farms, says Bill Van Allen, assistant general manager of the New Magma Irrigation & Drainage District, southeast of Phoenix. "It's rare to find cheap water. It's really rare to find free water," Van Allen says.

Eventually, Resolution will use that water for processing the ore. Peacey says the mine will use technology that recycles more water. "We've agreed to completely change the technology of some of the facilities to reduce the amount of water," she says.

But hydrologists and mining experts worry about the impacts of the mining and mine waste on local streams and aquifers, as well as the sheer volumes of water that the mine will draw from the desert. Resolution's "

, when the land sinks as the ore is taken out of the underground deposit. The subsidence will create a crater nearly 2 miles wide and 1,000 feet deep. This will affect the aquifer, says 

, an environmental geologist who is consulting for the San Carlos Apache Tribe, which opposes the project.

"If you blast a hole through that aquifer in that spot," he says, "the aquifer ceases to exist. But not only that, the water that would normally have [flowed] across that zone now just spills into the hole, and so it can't get to wherever it was destined to go."

The disruptions to water flows will be evident on the desert's surface, Wells says. "This is an extremely arid area, and springs and perennial streams are extremely important habitats. They're also extremely important to the local tribes as sacred places."

Locals are also concerned about Resolution's plans to store mine waste 

, and there are concerns about potentially releasing treated wastewater into Queen Creek, which was already polluted by historical copper mining. The 

, saying that treated-waste release into the creek would be a violation of the Clean Water Act. The tribe won on appeal, and Resolution is appealing to the Arizona Supreme Court.

But one of the biggest concerns is the amount of water that the mine will draw from the aquifers east of Phoenix. While Resolution has stored some Colorado River water for processing, the mine will also draw billions of gallons of water from the East Salt River Valley. In the 

2019 draft environmental impact statement for the mine

, the U.S. Forest Service wrote, "Cumulatively, the total demand on the groundwater resources in the East Salt River valley is substantial and could be greater than the estimated amount of physically available groundwater."

A Resolution spokesperson said the mining project knows the region is important for locals and habitats and noted in an email that Resolution is working with local tribes to minimize impacts on seeps, springs and streams, "using Indigenous Traditional Ecological Knowledge to inform the consultation process with Native American Tribes." The email also said that federal agencies have assessed the mine's pumping of the aquifer and put a "mitigation and monitoring plan" in place.

Mining companies say that it's important to develop these minerals domestically and that in other countries developing these resources, like China, the environmental impacts could be even greater. Pat Risner, president of South32's 

 south of Tucson, says the Hermosa mine will use technology to reduce and reuse water, especially in the mine waste. He says South32 has built a state-of-the-art water treatment plant so the project's water discharges meet state standards.

"You have to look at the trade-offs," Risner says, noting that much of global manganese processing is in China. "Compare the environmental impacts or the environmental footprint of that production versus a state-of-the-art, next-generation mine in the United States that has high standards."

But environmental groups worry that Hermosa is not implementing adequate environmental protections for local water. For example, there are concerns about the mine's water treatment plant and its novel method for removing selenium, one of the mining contaminants, before the treated water is discharged to local streams, says 

, an aqueous geochemist consulting for the groups. Selenium can have 

adverse health impacts on fish and other aquatic life

"It's important to increase our domestic supply of those metals so we're not dependent on other countries," Maest says. "But at the same time, we want to protect our natural resources. And in my experience, when you hurry up and do things, you might not be taking as good care."

South32 said in an emailed statement: "Hermosa project's new water treatment includes proven, patented technology for removing selenium" and that they "remain committed to protecting and conserving the region's natural resources, including closely monitoring and measuring water activities."

Locals worry that state water regulations for the mining sector lag behind

At the Cholla Canyon Ranch in western Arizona, Ivan Bender walks along a small wooden bridge, using a net to clear away algae from the turquoise waters of a hot spring.

The waters of the Ha' Kamwe' hot springs are healing and sacred, says Bender, the caretaker of the ranch, which belongs to the 

. Less than a hundred yards away, on the perimeter of the tribe's property, an Australian mining company called Arizona Lithium has been exploring for lithium, he says. Bender says the exploration drill holes have already led to reductions in the flow of the springs. He points to some holes scattered between the desert shrubs. "When they drilled that, that's what happened to our water," he says. "It went down."

"There's not enough water in the area," says 

, director of the Hualapai Tribe's Public Service Department. "So this is the wrong place to put a mine for lithium."

, the mining company based in Perth, Australia, that has begun exploration in the area, did not respond to NPR's requests for comment. The U.S. Bureau of Land Management, which authorizes mining on public lands, said in an email that the Australian company has just proposed an exploration plan, not yet a mine, and that "no decision has been made."

If the lithium mine does happen, this area in western Arizona isn't regulated by the state's groundwater act, says 

, director of the Arizona Department of Water Resources. He says much of rural Arizona has minimal groundwater rules.

"There's basically little to no regulation out there," Buschatzke says. "You have a common resource and a whole bunch of straws in the resource, and whatever the impacts are, the impacts are."

" for water, including the site of the Resolution Copper mine, the mining sector is exempt from key water regulations. Arizona's 1980 groundwater code requires that agriculture, industry and construction companies prove that the water wells they drill won't affect other water wells. That's not required for mining wells.

And the state relies on mining companies to self-report their water use because the law exempts mines from government monitoring. Buschatzke says his department compares reports across years and across similar users and will do an audit if the data submitted by mining companies "doesn't look right." But he doesn't like the word "surveillance." "It kind of implies Big Brother looking over your shoulder," he says.

"While we can enforce, it is better for us to work with folks to make sure they are achieving their regulatory requirements," Buschatzke says. "We are a regulatory agency, but at the same time, the best way to ensure regulatory compliance is to have positive relationships with the water users."

As for the issue of subsidence at the Resolution Copper mine, the Arizona Department of Environmental Quality said in an email that they "don't specifically measure the effects of subsidence on water quality. However, changes in water levels may have an impact on groundwater quality."

Other water-scarce regions offer warnings and solutions for the Southwest

Water-scarce regions like the American Southwest can look to places like Chile for a glimpse at a future of mining in an increasingly arid landscape, says 

, professor of mining engineering at Universidad de Chile and an executive at Shimin Engineering.

"Climate change took the mining industry in the country somewhat by surprise," Ihle says, noting that some mining companies in Chile have had to 

 because of the reduced water availability of aquifers.

"There are some mining companies, they do have clearance for extracting some water from aquifers, but they don't have the water," Ihle says. "They have the permit — they don't have the water."

This water scarcity poses a growing financial risk for mining companies, says 

, director of the Centre for Water in the Minerals Industry at the University of Queensland in Australia. "Water availability for them is a production risk much more than an environmental risk. So if they don't have the water they need to operate, the production can shut down," she says.

Mining operations in South America have been testing new technologies to reduce water usage, says

, chief executive of Lilac Solutions, an American lithium technology company. Lilac, which has been working on pilot projects in Argentina and Chile, doesn't use large evaporation ponds typical of lithium brine extraction. Instead, the company directly extracts lithium, a process that uses less water, he says. Snydacker says Lilac plans to start projects in the U.S. soon. "New technology is essential to ramping up lithium production to the levels required, while protecting water resources," Snydacker says.

The National Renewable Energy Laboratory is also researching direct lithium extraction, according to a spokesperson.

In the last decade, several mining operations in Chile have 

 to reduce impacts and not rely on local groundwater. Some Chilean copper mines are using pipes, some 

Arizona is also part of a multinational project that's building desalination plants in Mexico that would help supply the state, says Buschatzke of the Arizona Department of Water Resources. He notes that Phoenix-based mining giant Freeport-McMoRan is involved in the leadership and funding of the project.

"We haven't gotten that far yet about who the water would go to," Buschatzke says. "But clearly, Freeport's participation, in my mind, shows an expectation on their behalf that they're hoping to get some of this water."

A Freeport-McMoRan spokesperson said in an email: "To date, Freeport's participation in the 

 has been as a financial contribution. Freeport would hope to participate in any water development, but it is not a condition of our participation."

Climate change means the West may need to say no to some mines

The dryness of the West used to be a boon for miners, says 

, mineral resources program coordinator for the U.S. Geological Survey. "There's less vegetation, fewer trees," he says. "It's easier to explore for mineral resources where the rock is more exposed."

And some historical reasons explain why miners came westward. "The primary attraction of mineral resources in the West reflects the historical development of the United States," Williams says. "The West was a frontier — much of that became public land. Under the 

, there were opportunities to exploit those mineral resources."

But today, new mining technologies mean the U.S. can locate these critical minerals in less arid parts of the country, like the eastern Appalachians. William's agency recently received 

 at the country's mineral resources. "Relooking at some places in the eastern United States that were recognized as having potential in the past but were not really pursued because people were focused out in the Western U.S."

The energy transition will necessitate more mining for these critical metals, says 

, executive director of the Initiative for Responsible Mining Assurance. But she says there should also be times when state and federal governments say no to Western mine permits because of water concerns. "There's still going to be places where you say, yes, there's lithium in the ground here, but this is a no-go," Boulanger says. "We're going to have to make some choices in a world that's already experiencing the effects of climate change.

"What's not our drinking water today, in five years we may already be relying on it."

Support for this reporting came from the Bill Lane Center for the American West at Stanford University.

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As the U.S. plans new mines for copper, lithium and other metals to use in green technologies, mining projects in the West could threaten scarce water supplies.

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