Impact of mining activities on groundwater

Wpływ, działalności, górniczej

Mining activities, offering access to energy, metallic or rock resources, without which the functioning of the economy would not be possible, negatively affect groundwater.

The location and properties of the raw materials in question mean that they are mined by various methods – most often underground or open pit. However, regardless of the mining technique, extraction of raw materials often requires dewatering the rock mass with deep drainage systems and draining significant amounts of groundwater outside the extraction zone. Why? Because underground water, if it breaks into the workings, can pose a danger to the mine, the people working there and the equipment.

Due to the need to pump out large amounts of groundwater, the exploitation of the deposit may cause very profound changes in hydrogeological conditions in the mine area. The scale of the impacts of these phenomena varies and depends on many factors, both natural (geological structure, hydrogeological conditions) and anthropogenic (the extent and manner of mining operations).

As a result, underground mining, such as coal mining, as a result of intensive dewatering of the rock mass, is the cause of significant shortages of groundwater in the mining area. Open-pit activities, if only in the case of lignite, are the cause of large-scale depression funnels associated with drainage.

Impact of mine dewatering on groundwater

The most important factor determining the impact of drainage on the environment is the extent of the depression funnel. Due to the dewatering of aquifers, the groundwater table is lowered and a depression funnel is formed around the deposit, the extent of which can be tens or even hundreds of square kilometers in area.

At the same time, there are major changes in the water circulation system in the depression funnel area. In most cases, long-term groundwater pumping leads to the drying up of parts of the aquifers and the reduction of groundwater resources. As a result, there is a reduction in the efficiency or complete drying up of domestic water intakes or even deeper, municipal groundwater intakes.

The lowering of the water table also negatively affects the water level in reservoirs and watercourses. Due to the disappearance of underground recharge, the flow in rivers is reduced and the level of the mirror in lakes and reservoirs is lowered, and in extreme cases can even lead to the drying up of riverbeds and land depressions. On the other hand, in surface watercourses, which are the recipients of water from drainage, there is an increase in flows.

Another case of adverse impact of dewatering is the effect on soils. If the lowering of the water table has occurred in shallow near-surface layers, it can cause changes in the moisture content of soil, grassland, arable land and forestry. The symptoms are dryness and reduced yields of agricultural and forestry land. Within the range of the funnel of depression in marshes and wetlands, the water supply to the plant root zone may disappear, resulting in the transformation and degradation of natural plant habitats.

Dewatering of the deposit also adversely affects groundwater quality. This is the result of geochemical changes occurring in the pit (oxidation of various chemical compounds, which then enter the groundwater) and the dangers associated with the inflow of naturally saline water under conditions forced by mining operations. Additional foci of pollution, which affect the decline in groundwater quality, are all the infrastructure accompanying mining activities (landfills, waste dumps, industrial effluents).

Effects of mine decommissioning

As a result of depletion of deposits and due to economic aspects, mines are being closed in recent years.

One way to close a pit is to stop dewatering the rock mass. This is the simplest and cheapest way, which at the same time entails serious consequences for groundwater. This is because the process of restoration of water relations begins then, that is, the reversal of hydrogeological conditions that were artificially created by long-term mining operations. However, this type of activity is associated with a number of risks: deterioration of groundwater quality, flooding, reduction or complete disappearance of water flows in rivers, which until now have been artificially supplied with water from the mine. It can also be expected that waters will return to the natural channels of dried up watercourses, the occurrence of spillways or even flooding.

Decommissioning mines and stopping the drainage of the rock mass can have very serious consequences even for human safety. In some areas, housing developments built in areas of dried-up river valleys may be at risk of flooding. Therefore, in some cases, mine decommissioning may involve only the termination of the mining process, with the continuation of dewatering of the rock mass. In this case, the funnel of depression is not filled with water, and water relations remain altered.

The decision on how to decommission mining plants is made based on the law, taking into account environmental aspects and human safety.

Mining activities, in addition to providing valuable raw materials for the economy, also extract very large quantities of underground water to make mining possible and to maintain mine safety. Unfortunately, this activity brings with it a number of unfavorable changes. This manifests itself in the reduction of groundwater resources usable for the supply of good-quality water to the population and the economy, and results in long-term quality degradation.

Changes in the aquatic environment caused by mining activities can occur both during mining operations and tens or hundreds of years later. After some time, the waters will begin to clear naturally.

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