Seepage, runoff, and direct discharge are all ways that acids and heavy metals can pollute what?
Waterways, and by extension, the environment
Seepage is the process of something leaking, usually from underground. It can come from manmade sources (such as material leaking from a crack in a tank) or from more natural causes (I believe the formation of stalactites is a form of seepage, with mineral laden water slowly leaking into a cavern from the area above it).
Runoff is the process where rainwater will run along the ground down into streams and rivers.
Direct discharge is the pumping of waste water directly into a waterway.
All of these different ways that water can run to a waterway (such as a stream or river), when they come into contact with heavy metals and acids, can carry them into those waterways. The waterways themselves will transport them to bodies of water (such as lakes and oceans). And since all of these bodies of water are sources of water for the animals and plants touched by them, they can become polluted with the heavy metal and acid materials.