Summary #
Abandoned Mine Drainage (AMD) is water contaminated by contact with the physical environment created by past coal mining. It is Pennsylvania’s single largest source of nonpoint source water pollution and is characterized by four main components: high acidity, elevated metal concentrations, elevated sulfate levels, and excessive suspended solids. Understanding what AMD is and how it forms is the foundation for all watershed assessment and treatment work.
What is AMD? #
Abandoned Mine Drainage (AMD) is water that has become contaminated as a result of passage through a physical environment created by coal mining activities of the past. This contamination can occur in the underground voids created by deep or underground mining, or it can occur from water passing through coal mining refuse left on the surface.
The vast majority of AMD pollution results from old mining operations that were simply abandoned after the coal was extracted. In some cases the AMD originates from very old operations dating from the turn of the 20th century. Prior to 1977, laws governing coal mining were less stringent concerning environmental impacts. It was common practice to abandon mining operations following exhaustion of the coal reserve, then declare bankruptcy — allowing operators to walk away from liabilities, including environmental devastation.
The nature of AMD contamination varies greatly from site to site, as its formation depends on a variety of factors. AMD often lowers water quality and impairs aquatic life, and is most often characterized by one or more of four major components:
The Four Components of AMD #
Low pH (High Acidity) #
When mine drainage becomes acidic, it is referred to as acid mine drainage. Acid is a contaminant of primary concern because it can leach toxic concentrations of metals from rocks at mine sites. Acids in streams can corrode metal pipes and structures, break down concrete, and kill or stunt plants and aquatic life. Acidic runoff can also break down metallic compounds of iron, sulfur, manganese, and aluminum found in nearby rock or earthen waste piles.
For an explanation of how acid forms in mine drainage, see: How AMD is Formed.
High Metal Concentrations #
Layers of rock and earth above mined coal commonly contain traces of iron, manganese, and aluminum, along with other heavy metals. These metals can be dissolved through the action of acid runoff or washed into streams as sediment. Many metals, though common in nature, are toxic to fish and other aquatic organisms at high dissolved concentrations. Dissolved iron and iron precipitate can kill the aquatic organisms that fish feed on, clog fish gill structures, and smother stream channel food chains — all reducing fish populations.
Elevated Sulfate Levels #
As pyrite wastes are chemically broken down, sulfate compounds are produced in runoff waters. Sulfates can bond with water molecules to form sulfuric acid or attach to calcium atoms to form a gypsum sludge. Elevated sulfate levels are frequently found in AMD discharges.
Excessive Silt and Suspended Solids #
A significant but often overlooked threat to water quality comes from eroding soils at abandoned mining sites. Tiny fly nymphs, insect larvae, and other organisms that form the base of aquatic food chains can be wiped out by heavy accumulations of soil and mine waste particles washing into streams after rain events. Suspended silt can clog fish gills and smother eggs on the stream bottom. Streams muddied by suspended solids also increase costs at municipal and industrial water treatment plants and accelerate sedimentation in reservoirs.
Related Pages #
Source and Last Reviewed #
Content largely adapted from: EPA Region 3, A Citizen’s Guide to Address Contaminated Coal Mine Drainage, EPA-903-K-97-003.
Additional sources: http://www.epa.gov/region03/acidification/what_is_amd.htm | http://www.hedinenv.com/whatisamd.htm
Last reviewed: 2026-03 | Links may require verification — originally published pre-2010.
Tags: amd, acidity, metals, sulfates, practitioner
