Water draining from an adit (mine tunnel) that is discolored due to high amounts of metals and other chemical constituents.
The light colored rock pile in the center of the picture is a waste rock dump.
These are piles of rock that was excavated from the mine, but did not contain enough ore to be economically valuable. The waste rock does contain minerals such as pyrite that when exposed to air and water, oxidize to form acidic water.
Photograph of the Pennsylvania mine with numerous waste rock dumps surrounding a wooden structure.