Closed and abandoned mines monitoring

#geokinesia #closedmines #abandonedmines #geohazards #geotechnics #environmentalmonitoring #mosmin #remotesensing #insar #sar #spectralanalysis

Closed and old mines represent a huge and largely overlooked problem. Three out of five most contaminated sites in Canada are closed mines with the whopping clean up costs of over $5Bn.

In the USA there are over 160,000 old hard rock mines, where metals such as gold, silver and copper were once produced. The threat posed by these bygone miners remains largely unknown, the EPA (Environmental Protection Agency) admits that it has no system for monitoring the sites and does not possess any reliable information on which one could generate the next big toxic spill.

In South Africa, another large world mining region, more than 6,000 abandoned mines including 400 coal mines exist without any clean up plan or surveillance.

The situation is aggravated by the fact that the responsibility for the rehabilitation is often unclear, as some of the concessions are old, made under outdated standards, some operators went bust, not to mention illegal mining, which often has scale but exist outside of any legal or technical frameworks.

In any case, the ultimate responsibilities for the safety end up with the local or state governments, who sit on this “old mines bomb”, poorly prepared for a boom.

Closed or abandoned mine sites pose several types of threats.

Firstly, geotechnical. Old pits, waste rock dumps and tailing storage facilities (TSF) are large earth structures, some tailings can be several hundred meters high, and their movements, let alone a collapse, can be disastrous for the environment or the neighbouring areas, where settlements can often be found. And while TSFs and slopes of operating mines are closely monitored, those of old mines are not.

The risk is especially high in the seismic zones, where the stability today does not mean it will hold at the time of a seismic event. A good example is Chile, where 740 old and fragile TSF from the past copper mining represent a permanent threat. Another interesting thought is that changing climate patterns may trigger unexpected and previously unseen movements in the old mine areas, as increasing precipitation and storms may seriously disturb previously stable areas (see our previous Newsletters on changing weather patterns).??

Also, leftover underground mines pose a threat to the land surface stability, frequently leading to sinkholes formation, sometimes with catastrophic consequences. And while we have not seen many old TSFs’collapses, the examples of sinkholes caused by old mining operations sucking in territories, buildings or even complete settlements are in abundance.

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The case of Berezniki in the Perm region in Russia, where potash has been mined for years is exemplary. Poor monitoring and inefficient safety control and management resulted in a series of deadly accidents about 15 years ago, when gigantic sinkholes came about unnoticed and led to the collapse of the buildings and infrastructures with significant death toll.

Sinkholes around Berezniki and other towns in the potash mining area in Perm region:

Secondly, closed mines pose environmental risks, the most typical one is Acid Mine (or Acid Rock) Drainage – the leakage of the residual acid into the environment, often into rivers.

Some areas in Colorado, US or Yukon, Canada serve as vivid examples.

Thirdly, old leach pads and TSFs contain toxic materials, e.g. heavy metals and which can add to the trouble brought about by the leaking acid.

Monitoring of closed mines sites traditionally involves field campaigns and laboratory tests. This approach has obvious disadvantages being tedious and often difficult from a logistical point of view, especially for remote locations.

Moreover, it also has an intrinsic disadvantage of being discrete, which makes it hardly suitable for geotechnical monitoring.

Remote sensing can be a good answer to the problem. Despite certain limitations, its techniques such as InSAR can provide sufficient information on the areal geotechnical stability, while spectral, multi- and hyperspectral analyses can provide an insight into the key parameters and general health of the water, soil and vegetation. Even air quality can be analysed, for example, methane leakage can be detected remotely with sufficient reliability and accuracy.

Remote monitoring is irreplaceable for large areas screening and early warnings generation. Most of the geotechnical events show early predicates, which can be spotted early. Same holds for the environmental analysis, which is instrumental in tracking the dynamics and changes over some period of time. In general, a set of remote sensing techniques can equip a responsible body with a powerful and highly cost-effective tool to monitor the progress of the reclamation process as well as the risks to this process and the general site safety.

GeoKinesia is one of the world-leading InSAR service providers participates in the 12 members of the MOSMIN consortium, which includes Helmholtz-Zentrum Dreseden-Rossendorf (HZD) - a research centre from Germany, the Centre Tecnològic de Telecomunicacions de Catalunya (CTTC) from Spain, Babes Bolyai University from Romania, and a number of private remote sensing specialised companies and world leading mining companies such as Codelco, Boliden and Cumrumold. The aim of the consortium is to develop beyond the state of the art and promote remote sensing techniques to manage mines life cycle, but also provide the practitioners with practical tools to develop effective closed mines monitoring. These monitoring tools have to be put into practice better sooner than later, before the risks which are born by old mines materialise.