The Fate and Function of Acid Mine Drainage
For hikers and general wanderers who enjoy getting out into nature, the sight of a red earthed stream may be familiar. This unusual coloring is often an indication that the area may have previously been subject to mining operations. The excavations fill with water, and pollution seeps from the abandoned mines and waste piles. As water leaches out, this acid mine drainage (AMD) contains naturally high levels of acidity and dissolved minerals and metals, some of which are toxic. The AMD mixes with the surrounding water and causes an increase in acidity and concentration of toxic metals, a condition which impairs the water and prevents aquatic life from thriving.
Although systems to treat AMD have been created and implemented, areas exist where the water is still quite acidic. In order to better understand the fate of AMD, and why it persists in certain areas despite treatment efforts, Ohio Water Resources Center funded researcher, Prof. Elizabeth Herndon and her team are investigating the hydrology of the watershed to find the connections between the AMD system and the surrounding streams and ponds. Prof. Herndon is studying the Huff Run watershed, located near in Mineral City, OH. As its name might suggest, this area was previously a site of mining operations for coal and other minerals. Two thirds of the land surface have been affected by legacy mining operations, evidenced by mine refuse piles which stipple the landscape.
To gain a better understanding of AMD and its effects on the environment, I visited Mineral City to join Prof Herndon and her graduate student, Lindsey, in the field. I have seen rust colored streams before, but this extremely red/orange water was striking. They first showed me a catchment outlet, a channel parallel to the road, which receives a mixture of treated mine discharge and neutral stream water. Measurements taken at this outlet have revealed that the water acidity and dissolved metal concentrations are high, meaning there is still an undiscovered AMD source of this contamination entering the tributary. We then hiked into the main abandoned coal site. They pointed out the main treatment site: oxic limestone rock piles, which work by neutralizing the pH as the impacted water flows through. Next, they showed me a beaver dam area (beavers have been safely relocated), which separates the cleaned area from the area which still shows signs of AMD impact, despite the treatment efforts. Potential sources of AMD may be leachate from the surrounding refuse piles, contamination from groundwater trickling up into the surface water, or even drainage from an undiscovered mine opening. By taking a variety of samples at different times, Prof Herndon is able to collect information about the spatial and seasonal differences in discharge that may help unravel the complexities of the system. Tracking the water acidity, dissolved metal concentration, and where it meets the neutral water in different parts of the watershed can help determine how, when, and where the water is still being impacted – the key to determining how to capture and treat the remainder of the AMD water currently treated. This work may also provide a model for other watersheds that may be experiencing similar issues and will help watershed managers develop better strategies for implementing treatment systems, as well as providing more insight into the overall fate and function of AMD impacted systems.