Resolution Copper’s Ticking Time Bomb: Tailings, Floods, and the Risk No One Wants to Talk About
By Henry Muñoz, fifth generation miner, and Hispanic Conservation Leadership Council member.
Last year’s devastating floods through the Globe-Miami area weren’t an extraordinary event. According to the National Weather Service, Globe received 2.5 inches of rain in 24 hours, a level of rainfall that is not rare in this region. If such a relatively moderate event could cause this much devastation, what might happen under far more extreme conditions?
As we continue to pray for those affected, I couldn’t help but think about another kind of risk; one that remains largely unspoken: the proposed Resolution Copper’s mine at Oak Flat and the project’s tailings dam at Skunk Camp.
Resolution Copper, owned by multinational giants Rio Tinto and BHP, plans to open one of North America's largest underground copper mines near Superior, Arizona. The project includes a massive tailings storage facility, containing 1.37 billion tons of arsenic toxic waste held behind a dam nearly 500 feet high and three miles long, taller than the Chase Tower in downtown Phoenix, just ten miles south of the Pinal Mountains.
The proposed mine will export 25,600 acre-feet of water per year to the tailing’s storage site in the Dripping Springs-Skunk Camp valley, located upstream of the Gila River and which runs through Hayden, Winkleman, Kearny, and Florence.
The Final Environmental Impact Statement (FEIS) claims that the proposed Skunk Camp tailings facility would be designed to withstand the Probable Maximum Flood (PMF), the largest flood considered reasonably possible under current meteorological and hydrologic conditions. On paper, that sounds reassuring. But there are serious red flags:
The FEIS doesn’t include a final design for the Skunk Camp tailings facility. In other words, the design may change and a dam that can’t withstand the PMF could be finalized.
The FEIS completely ignores the possibility of infrequent, but extreme downpours in the future when estimating the biggest possible flood. It doesn’t say how large that flood might be, only that the tailings dam will somehow be built to handle it.
The Skunk Camp site would store over a billion tons of mine waste in a region that is both hydrologically complex and increasingly prone to extreme weather.
While this foreign company describes the proposed mine at Oak Flat as world-class mining, I call it gambling with my community’s future. Their record speaks louder than their promises. In Brazil, BHP’s Mariana dam collapse killed 19 people and poisoned 400 miles of river. In Madagascar, Rio Tinto’s mine contaminated waterways with uranium and lead. In Australia, Rio Tinto blew up 46,000-year-old sacred rock shelters at Juukan Gorge. Now they ask us to trust them with Oak Flat.
While this foreign mining company promotes the idea that the tailings dam will be “safe forever,” the truth is more complicated. There is no such thing as a structure designed to last for eternity. At the end of the project, Resolution Copper will walk away from this dam, and it will receive no further check-up or upkeep. This isn’t just speculation, it’s in the Final Environmental Impact Statement (FEIS) itself, which does not describe any plan for perpetual monitoring, inspection, maintenance, and review of the Skunk Camp TSF.
The mining industry itself acknowledges that tailings storage facilities are not built to last forever. As explained in the Tailings Management Handbook published by the Society for Mining, Metallurgy, and Exploration, these massive waste dams will eventually fail if not carefully maintained for as long as it exists.
It’s also important to understand the different types of risk. While the tailings pipeline would not run directly through any communities, a break could happen anywhere along its route, potentially threatening any community located downstream from that point. By contrast, a tailings dam failure would endanger those downstream from the dam itself. The Gila River Indian Reservation would be among the areas affected.
Resolution Copper’s tailings pipeline would intersect 13 Arizona State Trust Land parcels, and the proposed Skunk Camp tailings facility would cover another 19 parcels.
According to modeling presented in the FEIS, in the event of a tailings dam failure at Skunk Camp, mine waste could travel between 83 and 868 miles. That upper figure (868 miles) is not a theoretical extreme but the 75th percentile outcome, meaning that in one out of every four modeled cases, the tailings would travel even farther.
For perspective, the distance from Skunk Camp to the Mexican border (via Dripping Springs Wash, the Gila River, and the Colorado River) is roughly 425 miles, and from there to the Gulf of California, another 85 miles. Based on these data, in about 40% of modeled scenarios, tailings would reach the Mexican border during the initial event.
These figures underscore the scale of what’s at stake. A breach wouldn’t just devastate nearby communities, it could send toxic mine waste coursing through Arizona’s rivers, across the border, and ultimately into the sea. The Resolution Copper project is a potential and irreparable catastrophe waiting to happen. Let’s stop this mine at Oak Flat before it becomes the next headline in Arizona.
To learn more, listen to this podcast featuting Dr Steven H. Emerman, a hydrologist, geophysicist, and one of the world’s leading independent experts on mine tailings storage facilities.