Mine caps are protective covers installed over the surface of a mine to prevent access, limit pollution, and prepare the site for other uses. When a mine is taken out of production, the law may require capping to protect public health and safety. Mining firms can also cap old mines, sometimes working with environmental agencies, to address concerns about pollution. This work typically requires the services of a specialty firm with extensive experience in installation of mine caps to make sure it is performed properly and to any regulatory specifications.
In the case of an open mine, the mine cap can consist of filler soil along with concrete and other bonding agents applied to the surface of the mine to cover it. It can also be backfilled with clean soil and landscaped to prevent erosion and damage. Site restoration of this nature is not necessarily required, but may be recommended. The procedure involves the use of appropriate filler and liner materials to reduce the chance of leaks from below as the site settles.
Underground mines require capping of their shafts to prevent access. Mine caps may be made from concrete, steel, expandable foam, and other components. This capping keeps people out, which limits the risk of injuries and controls liability for the company. It can also be used to prevent leaks of potentially hazardous substances. In some cases, parts of the mine are closed off while others are left open to provide habitat for animals like bats, who may appreciate the amenities in mining caverns.
Additional measures may be required with mine caps for underground mines. The facilities may need to be ventilated and filtered to prevent problems from developing in the future. Pumping stations may also be necessary to keep water out of the mine, which can prevent sinkholes and cave-ins that might endanger the community. As a company prepares to take a mine out of commission, it can consult an engineer to determine which measures are necessary to meet environmental standards and address any other concerns.
Once capped, a mine can potentially be reopened, but it may require substantial work. In situations where a mine is temporarily closed, it may be secured by other means so it will be easy to restart production in the future, if desired. When it becomes evident that such sites are truly abandoned, they may be targets for mine caps. Some governments have policies that allow them to take over polluting sites to take appropriate measures, including capping. They can bill the former owners for these services if they can be located.