Solvay’s help to secure Roman mines in Bulgaria

The Chiprovtsi region in north-western Bulgaria has been actively mined for over 2,000 years. Gold, silver, lead, and other valuable materials have been extracted by civilisations dating back to the Romans. More recently, we established a fluorspar mine which was active until 2016. But when that mine closed and the site was handed to Industrial Function’s Environmental Rehabilitation (ER) department, they found themselves with a unique challenge.

The first step

Industrial Function’s ER department manages closed sites to ensure they pose no threat to people, fauna, or the environment and can be used for other purposes. One of the first tasks for the unit when they took control of the Chiprovtsi site was to close the entrances to the modern fluorspar mine. In consultation with the local authorities, the entrances were sealed with a one-meter thick concrete wall. The wall includes three steel pipes at the bottom to ensure that groundwater does not accumulate inside the mine entrance.

The Roman challenge

More challenging were the access points made accidentally by the previous operator between the modern and ancient mines. Again the local authority requested that they be sealed with concrete. Pierre Matz from Industrial Function’s ER cautioned: “The weight of a concrete barrier could lead to the slope collapsing into the mine. The solution was also very difficult to implement and would have been very expensive.”

The ER team, led by the local site manager Tihomir Atanasov, therefore advised against this option, and a better solution needed to be devised.

Netting — keeps people out, allows nature in

After further consultation with local authorities, it was agreed that we would install several large nets made from steel wire to block the entrance. Similar netting is used on roads where there is a danger of rocks falling. The netting has openings which are wide enough to allow bats and other small animals which use the cave to enter and exit. But is strong enough to prevent people and large animals from entering and potentially falling into the mines.

To ensure the heavy netting could be installed safely, the ER team looked for the Bulgarian company with the best experience and safety culture. After assessing the safety procedures and equipment of several companies, Corporate Health Safety & Environment (HSE) and the project team decided the selected Bulgarian contractor needed additional coaching. A highly regarded French company with experience in working in alpine environments was brought in to assist. The French team went through the procedures and equipment the Bulgarian team would use, and remained on site to assist.

Although planning and contractor selection were carried out in 2017, work could not begin until May 2018 due to weather conditions. On the first day the teams collaborated to understand how the safety equipment worked. Safety procedures, such as evacuating people in the event of an emergency, were also agreed.

Safe, on-time, and on budget

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

A happy ending

The success of the project is largely due to the good local management by Tihomir Atanasov and the Bulgarian team. There was also close collaboration with the corporate ER team who gave advice on the technique used to close the entrances. The professionalism of the two climbing teams also helped to ensure the job was completed without any safety incidents, despite a huge storm in the middle of the project. The work was also finalised on schedule and within budget.

Today, all entrances to the mines are closed, enabling Solvay to hand the mining concession back to the Bulgarian authorities, secure in the knowledge it will remain safe for decades to come.