The greatest contributor to both impaired water quality and land degradation in the Stonycreek watershed is coal mining that occurred before 1977. It has caused—and continues to cause—low pH and excessive quantities of toxic metals in streams. It is also responsible for the watershed's barren lands. How did this happen?
After underground coal mines close, surface water continues to infiltrate them. The mine pool builds up, seeking release wherever it can—through mine portals, ventilation shafts, or natural channels that offer the least resistance. The elements that water comes in contact with underground (e.g., iron and sulfur in the form of pyrite, as well as aluminum and manganese) will also be present when that water is discharged, along with compounds created by chemical reactions like the combining of oxygen and sulfate ions to create sulfuric acid. In addition, the combination of iron, water and oxygen forms ferric hydroxide, commonly known as "Yellow Boy." Almost all of these chemical reactions make the water very acidic (it lowers the pH), destroying the ability of the waterway to support fish and some plant life. These harmful discharges are commonly referred to as abandoned mine drainage, or AMD.
Surface mines, which by the 1950s were the dominant mining method in the Stonycreek, also contribute to AMD. They are responsible for barren areas called abandoned mine lands (AML). In surface mining, vegetation and overburden are set aside and the coal is removed. When restored properly, overburden is replaced, the land is restored to original contours, topsoil is laid down, and suitable vegetation cover is reestablished. This prevents potential contaminants from being exposed to air or water, and minimizes erosion. Unreclaimed or poorly reclaimed surface mines and coal refuse piles don't sustain productive plant life, making the sites subject to erosion and increasing sediment load in nearby streams. They are also an important source of AMD because they contain the same contaminants that are present in mine pools.
Today, slightly less than one percent of the Stonycreek watershed is classified as mining or "other disturbed surface" (e.g., sand and gravel pits). While most of the AML is unreclaimed surface mines, it also includes waste coal piles. About 80% of the watershed's AML acreage, totally nearly 2300 acres, is still un-reclaimed. AML sites are broadly distributed across the watershed, many in close proximity to streams.
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