On my desk are the Proceedings of the 2nd International Congress on Water Management in the Mining Industry. I would not presume to review the many papers therein. They range from the spectacular to the insane. There are many papers that remind us of the shortage of water in northern Chile and how tenuous mining is there, being so dependant on limited supplies of water. Seems desalination is the only solution to a certain supply of water for mining in the high desert.
Then there are many of those incredibly optimistic protestations that acid mine drainage may be eliminated by flooding, saturation, and below water storage. They include computer models “calibrated” to accuracies of decimal places. Which reminds me of my early years at university, when before the advent of computers, I worked with the professor of applied mathematics to prove there was no such thing as a valid calibration of a groundwater situation. Now with computers, one may spew out unpteen computer runs of a given situation and by brute force and smart persuasion, get some seeming correlation between piezometers readings and maybe outflow from a spring. Funny thing though, is that such proud claims of perfect correlation between the real world and the computer model seldom include a sensitivity analysis. The reason, I suspect, is the obvious: there is an infinity of combinations of permeabilities that can lead to correlation. All you need do is find one and your work is done. At least as long as the regulator accepts your report.
The fun part of new conference proceedings is comparing the papers to what is said on the web. Here is one random example. I do a little of the detective work—you can do the rest by piecing together the many web links to partial truths:
Collahuasi copper mine is located at high altitude, in an arid area of North Chile’s Andean plateau. Water efficiency is a major focus for the operation because it is a scarce resource, essential for the area’s biodiversity, and required in large quantities to pump water from deep wells.
Collahuasi reduces its impact on water sources by satisfying 75% of its water requirements with recycled water. Since 2008 it has used a tailings thickener that reduces water use by around 40 litres per tonne, while also bringing additional environmental benefits such as:
- Reducing tailings to a paste-like consistency allows sites to recover and reuse water, cutting their dependence on freshwater;
- Thickened tailings have a smaller volume and are more stable, so the tailings dam can have a smaller surface area and steeper sides; and
- Thicker tailings are less likely to contaminate ground water, since they are largely impermeable.
As a result of efficiency measures, Collahuasi has reduced its extraction of water from a local salt lake by 13% to 780 litres/second. As a result, the flow of a nearby spring has nearly doubled over the past two years.
At another link we read:
In March 2006, the environmental authority in the First Region issued a final resolution upholding the temporary groundwater extraction restriction, imposed in 2005, from wells located in the Coposa area. This resolution includes a gradual reduction in groundwater extraction based on the recovery of water flow at Jachucoposa spring. The programme will be suspended if Collahuasi transfers part of its groundwater extraction rights to the eastern end of Salar de Coposa. The project to so relocate water extraction rights is underway. The necessary environmental permits have been obtained.
In the proceedings we read:
A conceptual hydrogeologic model was developed for the Collahuasi mine area for the purpose of understanding directions of groundwater movement, evaluating structural controls on groundwater movement, and estimating input parameters for a 3-dimensional finite element numerical groundwater flow model. Analysis of available information indicates that the hydrogeologic system in the study area is highly complex.
Just as one would imagine in an area of jointed bedrock and multiple geological system. Sadly the authors of this paper do not provide us with the correlations between their computer model and reality. More on the complexity and the story of supplying the mine with water may be read at this link.
So even if you cannot get a copy of the proceedings which are not available on the web, you can go to the list of abstracts in the first link I provide above and do a web search on the mines mentioned to fill in the other side of the story. Enjoy.
