How Dewatering Affects the Mining Process

Dewatering and groundwater control is so important to mining in open pits and underground. Depending on geographical location and the level of the water table in the area, dewatering the site properly can make mining a success or not dewatering can break the entire project. That does not go without saying that it takes resources, planning, and management to execute the dewatering process. This can cost money and take more time then what was originally anticip0ated for the mining project duration. There are several more effects that dewatering has on the mining process, both positive and negative. When careful consideration is taken regarding the good and the bad effects, the best choice for the mining project can be made. 

The two primary objectives of mine dewatering are general mine dewatering and pore water pressure reduction. General mine dewatering is the process of which the surface water and groundwater inflows are intercepted and collected. The water is then pumped away to produce a site that is dry enough to make the relevant parts of the mine workable. Pore water pressure reduction focuses on the depressurization around shafts, pit bottoms, open pit slopes, and roadways. This process increases the strength of the rock and allows for better stability and safety for working with steep open pit slopes.

Positive Effects of Dewatering on The Mining Process

There are numerous effects of dewatering on the mining process that make the whole procedure worthwhile. General working conditions are improved along with an improvement in efficiency. The site becomes easier to dig out as well as the trafficking of equipment and materials becomes more efficient. There is also a considerable reduction in pit flooding induced downtime. The safety of the site can be maintained at the same time as allowing for a safer and more effective utilization of steeper open pit slope angles because of the reduction of pore water pressures and the reduction in groundwater levels.

There are positive effects on the financial aspect of the mining process as well when dewatering is used. When groundwater levels are lowered prior to beginning the mining work, blasting will produce dry blast holes. This cuts down the cost that would be incurred if more costly emulsion explosives needed to be used. In addition, the cost of hauling waste rock away is reduced when dewatering is utilized because dry waste rock and ore are not as heavy as wet material to haul away.

Potential Negative Effects of Dewatering on the Mining Process

The cost of the dewatering process can be a negative effect on the mining project because often it is spent during the pre-production phase or during the phase of production ramp up. It can take time to ensure that the benefits and the objectives of dewatering the mine are clear and to ensure that the dewatering scheme that is developed represents the most economical option for the mining project. It takes more time and money to do a hydrogeological assessment of the site and surrounding areas. Any method between pumping tests, desk study, numerical groundwater modeling, and borehole investigations can be used to meet this objective, and each of which requires equipment, personnel, and money to accomplish.

Another negative effect that dewatering can have on the mining process is related to water discharge management. Immense quantities of water will be produced from flowing drains, sumps, pumped wells, and surface water collection systems. This water that is produced is most often not clean enough to dispose of or use for any purpose. This means that costs will be incurred for the treatment of the wastewater. Usually, the treatment must be able to remove the suspended solids in the water before it can be used or discarded. The cost that will be incurred with wastewater management will depend on the water quality measurements including salinity, pH, and dissolved minerals. In addition, any water treated or not must be in full compliance with national and local regulations of the mining site. 

The Takeaway

There can be numerous challenges when mining underneath the groundwater level. However, when the proper consideration is taken and thorough planning is executed, dewatering a mining site can be immensely beneficial for the safety and efficiency of the mining project.

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