Abandoned Mine Drainage

                                                  
                              Aluminum Discharge                                                                     Iron Discharge
     white precipitate & milky blue, green or white water                                 orange preciptate

Abandoned Mine Drainage (AMD )
         Contaminating both ground water supplies and streams, abandoned mine drainage is not just an environmental problem that matters to fishermen or outdoorsy type folks. It pollutes a variety of drinking water sources. Treatment of wells with homeowner money or treatment of municipal water supplies with public money to remove these contaminants becomes expensive. To understand the extent of the AMD problem, it is important to understand how it started and why it cannot easily be solved.

                                   Water in the Mines       
          While local coal mines were in operation, ground water normally flowed into them, sometimes from the surrounding water table, but always from infiltration of surface water - rain or snow. This water was pumped out to allow mining to proceed. After the mines closed, the water still flowed in, but it was no longer being pumped out, so what are known as mine pools formed. 
         The water level in these pools just keeps rising until there is some sort of escape – an old airshaft or portal, a bore hole, a weak spot in the earth, etc. However, water is a wonderful solvent, and while sitting in the mines, chemical reactions take place as surrounding substances are dissolved.

Relationship to Coal Formation
         Coal was formed from plant material in prehistoric swampy areas. As these plants decayed, sulfur-metabolizing bacteria were at work on them. Iron compounds were part of the soil. Consequently, pyrite – a mineral comprised of iron and sulfur, was formed along with the coal. Once in constant contact with water in the mine pool, the pyrite dissolves into sulfur and iron ions. Ultimately these become the basis of sulfuric acid, which lowers the pH, and iron hydroxide, which coats stream channels with an orange “paste.”

The Big Four – low pH, Iron, Sulfur, & Aluminum             
          Highly acidic conditions are toxic to most living things, so the low pH represents a serious problem. Even in areas where acidity is not an issue, the iron hydroxide coating always is. It either smothers organisms who live along the streambed or prevents them from attaching to channel material. In either case, the foundation of the food chain is destroyed.
         One of the most common substances in the earth’s crust is aluminum, frequently found as aluminum oxide. One of its properties is the tendency to dissolve in acidic conditions. In this watershed, the mine pools are acidic and therefore they contain aluminum ions. Toxic to most life forms, this is a significant pollutant in Turtle Creek and some of its tributaries. As the pH of the water rises (as it becomes less acidic), the aluminum once again combines with oxygen to form solid particles which cause the “milky” look of the water or produce the white coating we see in some streams.
         In some areas magnesium can be a problem, forming a black precipitate.

Limestone                 
         As abandoned coal mines age, the material above, called the overburden, begins to fall into the tunnels. Geologically speaking, the next substance to be formed after coal and pyrite was limestone, and so the overburden normally contains a fair amount of that. This mineral has a high pH, and as it falls into the mine pools and dissolves, it helps to neutralize the water. Normally, however, not enough is present to offset the amount of acid, so our low pH problems exist.

Treatment
         In a nutshell, this is the process by which abandoned mine drainage occurs and how the four major components of the acid mine drainage we experience, low pH, iron, sulfur, and aluminum, became part of it. But this explanation also includes part of the solution. Both active and passive systems are used to treat AMD, with active being more costly and requiring more maintenance. In the Turtle Creek watershed we rely upon passive systems, but take a multi-faceted approach.

Learn More
         The following links will provide more complete information about AMD and related issues:
                   The Science of Acid Mine Drainage and Passive Treatment - Pennsylvania DEP
                   Turtle Creek Watershed Association 2005 AMD Strategy
                  

The design and implementation of this website has been made possible through assistance provided by the the Western PA Coalition for Abandoned Mine Reclamation (WPCAMR),  the Consortium for Scientific Assistance to Watersheds (C-SAW),  and the Pennsylvania Department of Environmental Protection's Growing Greener program.