Acid Mine Drainage in Local Watersheds

Background

Acid mine drainage (AMD), a type of non-point source water pollution, exists throughout the world and within our country, especially in Appalachia.  Each discharge degrades all water downstream, elevating mine drainage to a watershed level concern.  AMD comes from chemical reactions, uncommon in nature, which occur because mining exposes earthen layers to air and
water.  The orange result exterminates aquatic life.  Correcting these discharges requires building a specialized treatment system specific to each site’s water chemistry.  Many organizations and individuals cooperate to construct these systems.  Broadening awareness enlists community support.  Community support is the first step to treatment and remains our greatest chance to eliminate this pollution.  

To learn about mine drainage we must examine its effect on watersheds: how water obtains pollutants from mines, the effect of one particular pollutant – iron oxide – on aquatic and human life, and options to remove these pollutants from our waterways.  

 
How Abandoned Mine Sites Contaminate Water

Underground mines and surface mines expose rocks and minerals to air and water; consequences accompany this human-made alteration.  Pyrite is the most common mineral in coal mines.  Pyrite is also called Iron Disulfide (FeS2) and more commonly known as “fools gold”.  Physical weathering of the pyrite is essential to reduce the grain size of the mineral.  The early miners inadvertently accelerated this process by grinding up the ore and dumping the overburden in the mine tailings piles.  The first reaction, takes place within the mine.  Here, this mineral bonds with oxygen, producing sulfate and ferrous iron.  The reaction generates one unit of ferrous iron for each unit of oxidized pyrite.

When this water exits the mine, it contacts oxygen, causing the second reaction to occur.  Ferrous iron oxidizes, forming ferric iron.  Certain bacteria can metabolize iron, and increase the rate of the reaction, if in this situation the pH value nears 5.  At lower pH values these bacteria do not exist, in which case the process of oxidizing iron slows.  Also at this time, sulfur from the first step may evaporate as gaseous sulfate compounds (SO4-), or a rotten egg scent.  Losing aqueous sulfur sometimes elevates the water’s pH.  This reaction is the “rate determining step” in the overall acid-generating sequence.

Hydrolysis of iron transpires as the third reaction, responsible for splitting water molecules.  Formation of ferric hydroxide precipitate (when dissolved iron becomes solid, granular sediment clouding the water or settling on the stream channel bottom) depends upon pH.  This orange sediment is also called iron oxide, rust, or yellowboy.  If the pH is above 3.5, this sediment becomes visible more quickly.  If it is below this value, little or no solids will form; instead, these heavy metals will remain dissolved in the water, often unseen.

The result of abandoned mine lands’ chemical reactions with air and water produce widespread non-point source pollution that is difficult to remediate.

Iron Oxide’s Effect on Aquatic and Human Life

The layer of iron oxide on creek beds is not toxic to humans, though it is lethal for aquatic life.   For humans, this silt-like iron solid is not dangerous to touch or smell, unless the discharge also contains poisonous heavy metals like aluminum.  Aquatic macroinvertebrates (underwater insects, insect larvae, and crustaceans without backbones) respond to this iron coating in the same manner as any sediment.  They die from buried habitats and clogged gills.  Without the presence of these prey species, fish no longer live in affected waterways.  Mine drainage in any tributary negatively impacts the biodiversity of all water downstream and the human activities that thrive on that water and its biodiversity.

Remediation for This Pollution

Remedying this orange waste entails cleaning the polluted water near the place it first emerges into the air.  Cleaning this water may be accomplished with chemical treatment, wetland ecosystems, or a combination.  Remediation techniques are relatively new and develop rapidly.  However, two certainties do exist.  Treatment must be specific to each site’s unique water chemistry, and establishing such a system requires a team of community organizations, government agencies, engineers, scientists, and businesses.

Smaller groups and individuals play essential roles both directly and indirectly in site treatment.  Directly, they act as part of the remediation team described above, assist with treatment preparations such as water monitoring, and build vital community support.  Outside of direct treatment, educating others about orange water is one of the most important tasks to complete.

Hands-on education projects facilitate connections between people and their local environment.  Possible projects for non-point source pollution other than AMD include removing litter, planting trees on a stream bank to control soil sedimentation, or managing large amounts of animal waste.  Addressing AMD by repairing other forms non-point source pollution reinforces a watershed view.

Employing any of the multiple uses for iron oxide pigment including tie-dye shirts, paints, and chalk, builds awareness in its makers and fashions a market for the compound that will be supplied perpetually.

Remediation in every country, state, and town where this drainage exists is essential.  Over 350 western Maryland stream miles suffer from this devastation.  While each discharge spurs a long reach of damage, one treatment system cleanses many miles of stream.  Restoration continues while communities obtain funding, advance awareness, and organize widespread support.