I am not sure that there is anything than can very usefully be called as "average composition of acid mine drainage." In 1999, Geoff Plumlee of the U.S. Geological Survey published a very important paper called The Environmental Geology of Mineral Deposits (in G.S. Plumlee and M.J. Logsdon (Eds.). The environmental Geochemistry of Mineral Deposits, Part a: Processes, Techniques, and Health Issues. Society of Economic Geologists, Reviews in Economic Geology, Vol 6A, p. 71-116). Dr. Plumlee’s thesis, backed by a very large set of water quality and other geochemical evidence, is that the actual expression of the weathering of mineral deposits is a function of the underlying geology and the details of the weathering process (e.g., what sort of climate the weathering occurs in, the nature of the watershed processes, and other Earth-science factors). For example, one sees acid-mine drainage systems with pH values ranging from 2 (or even lower in extreme environments) to circum-neutral, with the observed pH essentially a factor of how much carbonate mineral presence there is in the ore body and along the flow paths. Sulfate concentrations ranging from perhaps 1500 mg/L (or even lower in the early stages of AMD in some ore-deposit types) to 50,000 mg/L or even higher. With the range of pH values, one sees widely ranging dissolved metals concentrations, and the nature of the metals depends overwhelmingly also on the nature of the ore deposit. For example, in Mississippi Valley Type deposits, we may expect to see elevated Pb, Zn and Cd, but would not expect to see very high concentrations of Cu. However, in Volcanogenic Massive Sulfides, one may expect to see Cu together with Zn and Pb.

Water-quality criteria you can obtain with a Google search. If you specifically want WHO standards, include then in your query. Almost any such inquiry also will return links to US Environmental Protection Agency standards, and others from Europe and Australia that may be relevant.

Depending on where you are and some other circumstances, it may not be very easy, or even practicable for you to find the Plumlee article. Here are a couple of suggestions:

• Tell us the kind(s) of ore deposits that concern you. Then we can focus our thoughts and data more usefully for you
• Write me off line, and I’ll see what I can do about getting you access to the USGS work and some other sources.

Well, i need to know whether you are looking for composition of AMD from coal mine or metal mines, or both, because the metal concentrations significantly varied between two.