Contaminated water from closed and abandoned mines impacts tens of thousands of stream miles. But what if these waters could be turned into an asset instead of a liability? New remediation options could significantly reduce the risk of accidental releases and even make mine water usable for fracking and other industrial processes.
There may be as many as 500,000 abandoned mines in the U.S., mostly in the western, mid-Atlantic and Appalachian states. Many of these mines were closed prior to the passage of the 1977 Clean Water Act. A large percentage of these abandoned mines have simply been left to drain contaminated water, known as Acid Mine Drainage (AMD), into local streams. Others have been closed by plugging the mine openings and building containment pools for mine water and contaminated tailings.
Because mining activity takes place well below the water table, closed and abandoned mines will gradually fill with water when left alone. These rising waters can cause holding ponds to overflow and add stress to containment walls, increasing the chances of a rupture. The Gold King Mine accident was a dramatic reminder of the danger that lurks in closed and abandoned mines. But thousands of other mines are already discharging toxic water into the local environment or are at risk of catastrophic failure in the future. In Colorado alone, 230 mines tracked by the EPA are releasing the equivalent of one Gold-King-size discharge every two days.
Contaminated mine waters can have devastating effects on the local environment. Water impacted by AMD is undrinkable for humans and wildlife and uninhabitable for aquatic plants and animals. Impacted streams can sometimes have a pH similar to that of battery acid, low enough to burn human skin and kill fish and other aquatic life. This acidic water further dissolves heavy metals such as copper, lead and mercury in the surrounding rocks, causing them to leach into streams and groundwater and build up on the banks of waterways. Waterways can carry these toxic elements miles downstream, impacting lakes and reservoirs far removed from the original source of contamination.
The total impact of AMD on local economies is difficult to estimate, but may be in the billions of dollars annually. If AMD impacts ponds and waterways used for fishing and irrigation, losses for local farmers and commercial fisheries can be devastating. Many areas impacted by AMD are also heavily dependent on tourism, creating significant disruption in local economies if waterways become unusable. And if drinking water sources are contaminated, local communities may need to bring in water from distant sources at considerable expense.
Even if the original contamination source is contained, these impacted streams and the surrounding local environments will take decades or even longer to return to their natural state without further mitigating action. If the source of pollution is not contained or treated, damage can continue effectively in perpetuity, resulting in an essentially permanent loss of valuable land and resources for farming, fishing and recreation.
A single mine pool can contain millions of gallons of water. Left untreated, that water represents a significant environmental and economic risk. However, innovative new treatments could make this water usable for other industrial purposes.
Water use has become flash point for fracking and other water-intensive industrial processes, especially in the drought-stricken western states. A single gas well can use up to 5 million gallons of water between initial fracturing and well completion. Using AMD instead of freshwater allows fracking companies to reduce their environmental footprint significantly and reduce friction with local communities. Done right, using AMD for fracking can be a win-win for developers and the environment.
However, in order to make mine water usable for fracking or other industrial purposes, the treatment must remove both heavy metals and sulfates. Many AMD treatment options remove only metals, leaving high levels of sulfates behind that can interfere with fracking fluid chemistry and make the water unsafe to release into the environment. Conventional precipitation methods generally are not able to reduce sulfate concentrations much below 1,200 mg/L. Membrane-based processes are more effective, but are very costly and generate a large waste stream.
However, new technologies are now available that can economically and effectively remove both metals and sulfates from contaminated mine water in one process. One example is HydroFlex™, a water treatment platform developed by Winner Water Services, a subsidiary of Battelle. In demonstration projects, HydroFlex has been shown to reduce sulfate concentrations by up to 90%.
These new technologies can help the industry significantly reduce the environmental and economic risks of AMD. Instead of waiting for the next Gold King-style accident, or allowing abandoned mines to continue to leak, we can turn all that water into a usable resource. That’s a triple win for industry, local communities and the environment.