South32 today announced completion of its voluntary remediation project at the former Trench Mine, a closed mine last operated more than 50 years ago on the present-day Hermosa Project site. 

The project involved remediating tailings from historic mining activities. Previously, the tailings had high moisture content and were placed directly on native ground. This type of tailings storage facility (TSF) allowed for stormwater to soak through and enter local waterways during heavy rainfall, carrying heavy metal contaminants. 

The TSF has now been redesigned as a dry stack system, which means the tailings are highly compressed with low moisture levels. A multilayer liner system with sophisticated lead detection underlays the tailings, collecting rainwater that soaks through and directing it to an on-site treatment plant. 

The remediation work was completed in accordance with the Voluntary Remediation Program (VRP) of the Arizona Department of Environmental Quality. The approach adopted, which was selected to ensure the highest standards of safety and water conservation, cost over $30 million. 

The project, commenced in 2017, involved over a million work hours from South32 employees and contractors, most local to Santa Cruz County. 

Pat Risner, President of the Hermosa Project, said “South32 works to high standards because that matters deeply to our stakeholders, whether they own wells downstream from our site, livestock close to the waterways, or shares in our company. It also matters deeply to all of us who work at Hermosa. We need to be able to hold our heads high when we talk about our work, and I’m proud to say that our project team can do that.” 

“South 32 has done a great job in designing and working with the VRP to ensure that we have the right system in place to address everything that’s coming off their property, to include their future processing,” said VRP program director for ADEQ Laura Malone. “It’s a win for the environment, and that’s first and foremost. It’s a win for South32, because they have a viable mine site, and they’re going to be able to be in that area for a long time. And it’s a win for the agency, because we know we have a site that is being managed appropriately and works well with the agency to address any of our concerns.”