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
