Remediation of Acid Mine Drainage in the North Branch of the Potomac River
An AMD-impacted stream in western Maryland that's been tinted orange with iron pyrite.
Acid mine drainage from abandoned coal mines occurs throughout the Appalachians. It is a significant threat to water quality in the upper Susquehanna River including the West Branch, the Juniata River, and the North Branch of the Potomac River, as well as to its tributaries in West Virginia and Maryland.
Acid mine drainage results from the reaction of pyrite (iron disulfide) with oxygen and water, producing iron hydroxide and sulfuric acid. Pyrite is frequently found in high concentrations in coal and bedrock in anthracite and bituminous producing regions of the Appalachians.
AL researchers have been working with the Maryland Bureau of Mines to determine the effectiveness of limestone dosers, and other acid mine drainage treatments, in improving water quality throughout the North Branch of the Potomac River.
How do you treat acid mine drainage?
Acid mine drainage is very difficult to treat, and many treatment techniques have been developed to mitigate acid drainage including constructed wetlands, SAPs, anoxic limestone drains, limestone dosers, etc.
Why is acid mine drainage a problem in the North Branch?
Studies from the late 1980's targeted the North Branch of the Potomac River watershed as a substantial source of acidic water as a result of AMD. Twenty of 70 subwatersheds in the North Branch were identified as acid mine drainage producers with a total acid input into the system of over 11,000 pounds per day under low flow conditions and approximately 35,000 pounds per day during high flows.
For the North Branch, limestone dosers would provide the best method to treat large volumes of water on a daily, continuous basis. Using available water quality data, a model was developed to strategically site a number of limestone dosers to neutralize acid mine drainage in the North Branch. Four dosers were initially installed in the North Branch watershed. By the end of 1997, five dosers were installed at these locations as shown in the figure below. In December 1998, a sixth doser (not pictured) was added to the array at the Kempton deep mine complex air shaft.
The figure below depicts sources of AMD, as well as dosers locations, for the North Branch project:
Did acid drainage abatement work in the North Branch?
Prior to doser installation, mean annual pH values in segments of the North Branch were below 5.0, with many falling below 4.0 during low flow periods. After doser installation, mean annual pH rose to over 7.0 for most of the North Branch.
This project restored 26 miles of the North Branch above Bloomington Dam, improved water quality in Lake Jennings Randolph, improved 8 miles of tailwater below the dam, and restored 8 miles of tributary waters.
The figure below shows the improvement in pH observed following the doser installations:
Young rainbow trout collected from the North Branch.
Were there biological improvements?
With increased pH in the North Branch mainstem, fish communities have shown gradual recovery over time, in numbers and size. Currently, trout are stocked and provide an additional recreational resource. Insect communities are also making a comeback, but they have been hampered by poor substrate quality -- a remnant of yellowboy deposition. Over time, flood events will scour the yellowboy out of the system and the insect community will improve as the substrate returns to a more normal habitat. Stoneflies are now being seen at many stations in the North Branch system -- an indication that recovery is taking place.
Acknowledgements:
"Remediation of the North Branch of the Potomac River" was a multi-year project funded by the Maryland Department of the Environment, Water Management Administration, Mining Program, Bureau of Mines.
Project PI: Dr. Raymond P. Morgan II