Acid mine drainage from underground mines occurs as:

Correct option is B

Acid Mine Drainage (AMD) is the outflow of acidic water from mining sites, especially coal and metal mines. It occurs when sulfide minerals (such as pyrite, FeS₂) react with oxygen and water to form sulfuric acid. This acidic water dissolves toxic heavy metals, leading to severe environmental damage.
For underground mines, AMD typically occurs as "Point Discharge." This means the acidic water is released from specific, identifiable locations like mine entrances, shafts, or tunnels, unlike surface mines, where it can be diffuse or non-point in nature.
Information Booster:
· Formation of Acid Mine Drainage (AMD):
· Reaction: 4FeS2+15O2+14H2O→4Fe(OH)3+8H2SO4
· This produces iron hydroxides (yellow-orange deposits called "Yellow Boy") and sulfuric acid, making water highly acidic.
· Effects of AMD:
· Lowers pH of water bodies (as low as 2–3).
· Leaches heavy metals (iron, copper, arsenic) into water.
· Destroys aquatic ecosystems by killing fish and plants.
· Control Measures for AMD:
· Limestone Treatment: Neutralizes acidity using calcium carbonate (CaCO₃).
· Wetlands & Bioreactors: Uses bacteria to remove sulfates and raise pH.
· Mine Sealing: Prevents oxygen and water entry to stop AMD formation.
Additional Information:
· Point Discharge vs. Non-Point Discharge:
· Point Discharge: Fixed, identifiable source (e.g., mine shaft).
· Non-Point Discharge: Diffuse pollution (e.g., rainwater runoff).
· AMD in India:
· Jharia & Raniganj coalfields (Jharkhand, West Bengal) are heavily affected.
· Government regulations like Environmental Impact Assessment (EIA) address AMD control.
· Global Case Studies:
· Pennsylvania, USA: Extensive AMD from coal mines affects rivers.
· Ok Tedi Mine, Papua New Guinea: Severe metal contamination due to AMD.