rain age ▁( also ▁known ▁as ▁A MD ) ▁is ▁a ▁form ▁of ▁water ▁poll ution ▁involving ▁water ▁that ▁has ▁been ▁poll uted ▁by ▁contact ▁with ▁mines , ▁typically ▁coal ▁mines . ▁Although ▁it ▁is ▁sometimes ▁called ▁" ac id ▁mine ▁d rain age ", ▁not ▁all ▁abandoned ▁mine ▁d rain age ▁is ▁acid ic . ▁ ▁Types ▁The ▁most ▁common ▁form ▁of ▁abandoned ▁mine ▁d rain age ▁is ▁acid ▁mine ▁d rain age , ▁which ▁is ▁highly ▁acid ic ▁water ▁coming ▁from ▁mines . ▁Ab andon ed ▁mine ▁d rain age ▁can ▁become ▁acid ic ▁when ▁it ▁is ▁exposed ▁to ▁o xygen ▁and ▁sul fur - cont aining ▁min er als ▁such ▁as ▁py rite . ▁ ▁Another ▁form ▁of ▁abandoned ▁mine ▁d rain age ▁is ▁al kal ine ▁mine ▁d rain age . ▁This ▁typically ▁occurs ▁in ▁the ▁presence ▁of ▁min er als ▁such ▁as ▁cal cite , ▁lim estone , ▁or ▁dol om ite . ▁The ▁third ▁form ▁of ▁abandoned ▁mine ▁d rain age ▁is ▁metal ▁mine ▁d rain age , ▁which ▁occurs ▁when ▁large ▁amounts ▁of ▁met als ▁such ▁as ▁lead ▁cont amin ate ▁mine ▁water . ▁ ▁Ge och em istry ▁The ▁precise ▁chem istry ▁of ▁abandoned ▁mine ▁d rain age ▁dis charg es ▁typically ▁var ies . ▁Ab andon ed ▁mine ▁d rain age ▁typically ▁origin ates ▁in ▁surface ▁mines , ▁deep ▁mines , ▁and ▁" g ob ▁p iles ". ▁ ▁Ab andon ed ▁mine ▁d rain age ▁typically ▁has ▁high ▁concentr ations ▁of ▁met als