The source of the odor was decomposing garbage.
In a normal reservoir, there's an abundance of fish, shrimp, algae, and various microorganisms. However, in the seepage tunnels of such a coal mine, living creatures are exceedingly rare and particularly uniform.
Occasionally, there might be some fish and such, barely alive, making it even harder to form an ecosystem like that of a reservoir.
The garbage dumped here decomposes especially slowly.
When the heavy machinery began operating, some of the exposed decomposing matter started to emit odors under the sun's baking.
The complexions of the mining bureau's leaders grew even worse.
Garbage landfills aren't forbidden, but there are strict regulations. For example, Unity Coal Mine at the foot of the mountain was an open-pit coal mine on its shallow layers. Several communes invested in its creation, and it was quickly exhausted. The exposed mining area eventually turned into the Zi Feng Town garbage landfill.