what chemicals are being leached into the water?

Answer 1

you need to be more specific on where the water is coming from.

Coal mine drainage leaches sulfur into the water.

iron is naturally leached into water from running through rocks under ground.

Calcium carbonate is another natural chemical leached into the water from water the runs under ground.

In gold mining areas miners used to use mercury to get gold out of the ore. This process leached mercury out into the water.

Another process used arsenic. Again arsenic was leached into the water.

You need more details to get a good answer.