Dewatering and pit and mine reclamation
What happens once a mine is closed?
The usefulness of a mine may span from a few years to a few decades. However, once the mineral resources are used up or operations are no longer profitable, crews aren’t able to simply pack up and leave. Federal and state agencies have regulations that decide the correct way to close, decommission, and remediate a mine.
After closing, a mine might be reclaimed for other purposes or restored to its pre-mining condition. The majority of regulatory agencies demand a mine closure plan prior to granting a mining permit. Regulators may also need a financial guarantee that an operation will be able to pay for the dewatering and reclamation processes that a successful pit and mine closure needs.
Note: Louisiana’s major “mined” products are natural gas and petroleum. Salt, sand, coal, sulfur, and gravel are also extracted in Louisiana. When “mining” is mentioned in this article, this could be referring to hydrocarbon extraction for the oil and gas industry, or the surface mining of materials used to produce concrete and build roads. The essentials of dewatering pit and mine reclamation remain the same.
Pit and Mine Dewatering
Quarries, pits, and mines can unfavorably affect surface and groundwater in several ways. This is why mining operations are accountable for treating and capturing contaminated water and mine sediment on-site.
Constructing a mine below groundwater level can also create operational problems, which dewatering can address. Mine dewatering means inputting groundwater control strategies like in-pit pumping, perimeter dewatering wells to catch lateral groundwater flow into lower groundwater levels, cut-off walls (slurry walls holding groundwater back from deposits), and the pit. Mine dewatering can help this by:
- Decreasing haulage costs (waste rock and dry ore weigh less when dry);
- Increasing slope safety and stability (lower groundwater levels allow for use of steeper slope angles);
- Decreasing blasting costs;
- Decreasing downtime caused by pit flooding.
Mini-excavators and dredgers can function in shallow water as well as completely underwater to help mining operations with dewatering and dredging efforts. Mechanical dredging by MSHA-certified operators clears tailing ponds, while the same machines can construct stopbanks, levees, embankments, dikes, or floodbanks to keep excavation operations dry and manage water flow.
Mine Closure Process
It usually takes years to properly close a mine, but more time may be needed if long-term water treatment or wetlands monitoring is necessary. Mine closures consist of the following steps:
- Shutting-down: Once production has stopped, some contractors or workers will remain at the site to remove equipment and shut down operations;
- Decommissioning: During this step, parts and equipment are removed and cleaned, pipelines are drained, buildings and other structures are demolished or repurposed and waste is removed from the site;
- Reclaiming/remediating: This step is a long process designed to return the land to a satisfactory standard of productive use, and ensure that water sources close by have acceptable water quality. Reclamation workers need to remove hazardous materials from the site, plant native trees and grass, and restore topsoil. You can view Louisiana’s recommendations concerning spoils, embankments, and high walls at abandoned mine sites (PDF) here;
- Post-closure: Continuous monitoring programs show whether or not reclamation efforts were successful. Long-term maintenance processes may involve treatment of mine discharge water, evaluation of the progress of coastal remediation efforts, and occasional monitoring of the effects of ore and other residue left behind.