Reclaiming old coppermine: new tailingsdam leakage problem 1

[pimheinkool]

An old coppermine tailings dump is reclaimed using high pressure hydraulic monitoring. The resultant slurry is being processed in an acid leaching plant. The remaining tailings are pumped to a newly constructed tailings disposal facility (new tailings dam). Preliminary hydrogeological studies indicate a possible leakage of 2,000 m3/day at the newly constructed facility. To me, this seems quite a lot. What's your opinion? Many thanks in advance, Pimhein Kool

 

[PBroad]

"Leakage" from a dam is necessary to maintain stability. This leakage however must be controlled and fed to a water treatment system. If a dam did not leak it would be thixotropic and would fail catastrophically if shaken, ie earthquake. Suggest you get a local licensed enginner to look into your specific needs.

 

[nobudy]

there are several questions arise Firs t if what is the gelogical structure under the holding pond and the dam materail . short term fix colud be the use of a pond liners often used inforestry setings where the soil will not seal to with hold water. also the use of poplars in the taling pile will will trap the hevey metales

 

[Hardrockminer]

If you have designed this dam without understanding the hydrological regime in the area, the characteristics and chemistry of the tailings, and engineered the dam to allow you to intercept and collect the seepage you have been pretty negligent unless the seepage is benign which sounds unlikely in the circumstances.

You do not say what the chemistry of the liquids is? pH? but probably it is relatively high in copper iron and low pH. If so the treatment of this material is pretty straightforward chemistry but you have to corral it before you can deal with it.

You,also do not say whether the seepage is occurring through the dam face? through the bottom into ground water? or coming out through an underdrainage system designed to collect it.

You should be aware that all dams leak somewhat particularly gravity (earth fill dams) These are really controlled seepage barriers and as pointed out above rely on managed seepage to maintain their stability. The issue is the phreatic surface (essentially the saturated water surface). If this rises so that the phreatic surface intersects the face of the dam then seepage on the dam face will occur and you will see water starting to flow at the toe of the dam. A small amount of seepage is normal but if it rises too high and you see water flow above the toe your dam is headed for failure and you must take urgent action to remedy the situation, particularly if you see turbidity in the water which is an indication that piping s occurring i.e material is being removed from the dam core and the dam will gradually weaken. Piping progresses hyperbolically so any evidence of piping must be taken as a sign that total dam failure may be imminent and immediate steps must be taken to lower the phreatic surface. These can include such methods as lowering the water stored on top of the dam, drilling wells into the dam face and pumping the water levels in the dam down, reinforcing the toe to raise the surface of the dam face back above the phreatic surface, placing dewatering structures into the tailings themselves (underdrainage)

My advice is, that if you have not already done so, have your whole tailings dam situation reviewed by an independant expert with specific experience in tailings dam design and get him to clarify the issues that you need to understand well to manage this dam properly.

The news amy not all be bad. Note that some things such as underdrainage will promote consolidation and higher densities in the stored tailings which will not only add stability but also increase the available storage capacity in terms of tonnage.

Good luck

Hardrock Miner

 

[pimheinkool]

Thank you Hardrock Miner and others for your extensive help.The use of an independent engineer solved my problems, but I'm learning a lot from your answers. Again, thank you for your help.
Pimhein Kool