The safe and secure closure of mining activities

The Chiprovtsi region of Northwestern Bulgaria has been mined for gold, silver and lead for over 2,000 years, and more recently for fluorspar by Solvay. When that activity stopped in 2016, though, the mine was handed over to Solvay’s Environmental Rehabilitation (ER) department to be safely closed down. The task, however, represented a unique challenge.

The ER department within Solvay’s Industrial unit manages closed sites. One of the team’s first tasks, when they took over the Chiprovtsi site, was to seal the entrances to the modern fluorspar mine with a one-meter thick concrete wall.

The Roman challenge

More challenging, however, were the access points that lay between the modern and ancient mines, made accidentally by the previous operator. Local authorities requested they be sealed with concrete too, but as Pierre Matz from Solvay’s Industrial Environmental Rehabilitation team cautioned: “The weight of a concrete barrier could have led to the slope collapsing into the mine. Additionally, implementing that solution would have been difficult to implement and very costly.”   

A better solution was needed.

Keeping people out, allowing nature in 

After further consultation with local authorities, it was agreed that Solvay would install a series of large steel wire nets to block the entrances. Similar netting is used on roads where there is a danger of falling rocks. The netting has openings wide enough to allow bats and other small animals that use the cave to go in and out, but it’s also sturdy enough to prevent people and large animals from entering and potentially falling into the mines. 

Roman-mines collage of images

To ensure the heavy netting could be installed safely, Solvay’s ER team looked for a Bulgarian contractor with high caliber experience and strong safety culture. Additionally, Solvay contracted a highly regarded French company with experience in working in Alpine environments for support. On the first day of the operation, the teams coordinated safety procedures to make sure they were aligned with Solvay’s high standards in that domain. 

Roman mines Infographic

Over the rest of the week, the teams worked seamlessly together. One-meter holes were bored into the rock, and a steel anchor shaft was fixed into each hole with glue. Finally, the netting was attached to the anchors to secure the entrance to the ancient mines.

Today, all entrances to the mines are closed, enabling Solvay to hand the mining concession back to the Bulgarian authorities, confident that it is safe and secure for decades to come.