안녕하세요.

abandoned mine drainage refers to the fact that in the process of mining (usually coal)

rocks containing iron and sulfur compounds that were not exposed to the outside, become exposed.

then these rocks can react with water and air, resulting in acidic water inside the mine.

acidic water can further allow other metals in the rocks to dissolve in the water as well.

when this water starts spreading out and mixing with other freshwater sources

this becomes a water pollution problem, known as acid (abandoned) mine drainage.

abandoned mine drainage has nothing to do with thermal pollution!

zero connection there, make sure you double check your notes.

hope this helps :D