Groundwater and Mining

The discipline of hydrogeology is essential for mining activities as a part of a complex geological-engineering knowledge. There­ are two main considerable connections between mining and water. First one is that mining activities mean a huge intervention in natural processes which is also true for the water cycle on regional scale. Furthermore, it is well-known that water can easily mobilize and transport natural and anthropogenic contamination. In the following, we can see the details of these two effects to make a better understand of mining–water connection. 

To understand the changes in water cycle we must keep in mind that – according to modern hydrogeology – in the saturated zone, under the groundwater level every pore is filled with water. Therefore, if the mineral is under the groundwater level, the water table must be sunk below. This is usually achieved by pumping wells creating a depression cone. The artificially generated depression can cause changes in the groundwater flow systems which may be a critical situation for GDEs (groundwater dependent ecosystems) and springs. As a hungarian example for this, the Tapolca Lake Cave or the Fényes-springs in Tata had dried in the second half of the last century due to nearby mining. After mining had ended, water appeared again.

Visitors in Tapolca Lake Cave

Source: https://bfnp.hu/en/tapolca-lake-cave-visitor-centre-tapolca

The drying of pores – caused by dewatering – can lead to compaction and subsidence of the surface which can damage buildings. In case of closing an open cast mine the lack of water drainage create a lake.

The development of mining lake

Source: https://ars.els-cdn.com/content/image/1-s2.0-S0048969712013976-fx1.jpg

This is different from a natural lake as there is no river flowing into the lake, its water is from groundwater, precipitation, and maybe surface runoff. In these lakes the rainwater and surface runoff can directly reach groundwater level without infiltration through the unsaturated zone which could clean it naturally. It means that the lakes in old mines make groundwater more vulnerable to contamination. Using the lake for watersports or as a fish pond can also pollute water. However, a biofilm can form on the lake bed after at least five years that works as a natural filter and clean the lake. Nevertheless, these lakes also decrease groundwater level due to intensive evaporation on the open water surface.

Contamination in connection with mining can cause very serious problems, such as the ecological disaster on the hungarian Tisza river in 2000, when a cyanide spill reached the river from a goldmine’s tailing pond in Nagybánya (Baia Mare, Romania). 

Source: https://www.unece.org/fileadmin/DAM/env/documents/2017/TEIA/GCE_2_June_2017/1_Peter_Kovacs_TMF_accidents.pdf

The most important object is to avoid the infiltration of contaminations during the mining activity and after the mine is closed. Acid pit water can dissolve heavy metals and cause damage.

Now, we may all see how important is the hydrogeological competence in mining to make it effective as well as sustainable for the environment from the beginning to the reclamation.