Acid drainage does not normally occur in areas before mines are built but tends to happen after the mine has been in operation for many years. what causes acid drainage?
a. concentrated acids used to dissolve metals from the rock are picked up in rainwater.
b. mining exposes unweathered rock surfaces that react with water and the atmosphere to generate acids.
c. the acid is already present in trapped underground pockets and is released by mining equipment.
d. abandoned mining equipment leaks acids from batteries.