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A solution to mine drainage?

When the U.S. Forest Service acquired land for the 607,000-acre Daniel Boone National Forest in Kentucky, a multitude of water-quality problems came with the deed.

Located in the mineral-rich foothills of the Cumberland Mountains, much of the land that now comprises the Daniel Boone has been mined for coal over the last 100 years. Once the rich seams of high-sulfur-content coal were depleted, however, owners simply walked away, leaving many of the abandoned mines to pollute nearby watersheds for decades to come. Although the mine abandonment occurred in the era prior to enactment of state or federal reclamation laws, little has been done until recently to fix the tremendous environmental damage.

In the southern tip of the national forest along the Kentucky-Tennessee border, portions of Rock Creek have suffered particularly heavy damage from acid mine drainage (AMD). Several abandoned mines have been pouring contaminated water into the watershed of this state-designated wild river for as long as 50 years. But this is not unusual--it is estimated that between 1 and 2 percent, or 10,000 to 20,000 acre-feet, of all water originating on the forest is contaminated by AMD.

Officials of the Daniel Boone, charged with improving the forest's water quality, working with the U.S. Forest Service's Berea Research Center in Kentucky, decided in the mid-1980s to pursue a relatively new technology that uses manmade wetlands to treat AMD-tainted water. Following the old adage that a drop of tainted water is cleansed once it flows over several stones, the new method for purging waterways of AMD consists of using swamplike conditions as a filter. It's not that simple, of course, but that's the basic idea.

Historically, the principal methods for treating acid mine drainage have been to seal the portals of unused mines or to add lime (an alkali) to help neutralize the acid in the discharge. In both instances, however, adequate treatment can be costly. In fact, Robert Kleinman, a research supervisor for the U.S. Bureau of Mines, has estimated that the nationwide cost to the mining industry for chemical treatment of AMD alone is $1 million per day. Sealing mine portals (usually with concrete) is not only expensive but often the water inside usually finds another way out.

In the spring of 1988, the U.S. Forest Service, searching for ways to solve the AMD pollution problem affordably, constructed its first manmade wetland for the purpose of treating AMD. The facility was created near the opening of the worst-polluting mine along Jones Branch in the Rock Creek watershed. Funding for the $161,000 project ($75,000 for the wetland and $86,000 for roads) was generated jointly by the U.S. Forest Service, the Kentucky Division of Abandoned Mines, and the U.S. Office of Surface Mining. Howard Halverson, a research scientist from the Berea Research Station who is an expert on this treatment method, was named project leader.

The Rock Creek wetland, as the project is called, consists of two shallow ponds that have a total surface area of 11,000 square feet. In this case, two ponds were required because there wasn't enough level land near the mine for a single facility (the wetland's size is determined by the amount of flow from the mine).

The ponds were built by leveling the floor of the two existing depressions, which are about three feet deep. The flat, compacted floor was treated with bentonitic clay to minimize see page, and then a layer of crushed limestone was placed on top. An additional 18-inch layer of mushroom compost was added to allow the growth of cattails and other aquatic vegetation vital to the cleansing process. Given some maintenance, mostly dredging, the wetland's life expectancy is estimated to be 40 years.

Once contaminated water from the mine reaches the ponds, treatment of the AMD begins immediately with natural geochemical and biological processes that remove and accumulate most of the 17 metals contained in the mine discharge. Metals are removed by naturally occurring filtration, ion exchange, and absorption by plants and other organic matter in the ponds. In other words, the vegetation works with the lime, compost, air, sunlight, and other natural processes to absorb, transform, filter, and collect metals and other harmful compounds.

After the first year of operation, Halverson admitted that he was pleasantly surprised by the effectiveness of the miniature wetland. Preliminary reports show that during the first growing season, the two-pond system reduced dissolved solids by 90 percent, eliminated 98 percent of the sulfates, and strained 100 percent of the iron from the mine discharge.

Remarkably, the wetland project also improved the pH levels in the mine discharge from a low of 2.9 to a high of 7.8, and maintained a pH level of 6.0 during the early part of winter. (This water quality is sufficient to support most fish life.)

Overall, the late-season results were less impressive, but better than Halverson had hoped for. Data collected during cold-weather months show that the wetland is a little more than half as effective as it is when the plants are green and growing during spring, summer, and autumn. Still, the system produces water that is able to meet U.S. Bureau of Mine criteria 80 percent of the time.

The results of some wetland treatments of polluted water in the past have been less than spectacular. Halverson attributes most of the failures to construction problems and a lack of periodic maintenance. "It's absolutely critical that the wetland is both large enough and flat enough to contain water from the mine discharge for a minimum of 12 hours," he insists.

Halverson says that the Rock Creek watershed experiment will require an additional two years of study before any concrete conclusions can be made. If the project continues to register positive results, however, he believes that additional wetland development can be expected on Rock Creek and elsewhere in the Daniel Boone National Forest in the near future. (Just recently, the Kentucky Division of Abandoned Mines approved funding for the construction of a second wetland project in the Rock Creek watershed. Eight abandoned mines presently contribute AMD to the Rock Creek watershed.)

To date, the Rock Creek wetland project appears to carry the hopes of many who are searching for a low-cost solution to the AMD dilemma that is currently impacting 7,000 miles of streams and rivers in the U.S.

Richard Wengert, supervisor of the Daniel Boone Forest, is convinced that the Rock Creek experiment shows great potential for the use of wetlands in curbing AMD and other forms of water pollution. And the benefits are enormous--for fish, wildlife, and the landscape's aesthetics--all at a cost much less than traditional methods.

For additional information about the use of wetlands to control AMD and other forms of water pollution, contact Richard Wengert, Forest Supervisor, Daniel Boone National Forest, 1000 Vaught Rd., Winchester, KY; 606/745-3165.

Soc Clay of South Shore, Kentucky, specializes in outdoor topics.
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Title Annotation:Watershed Wars; manmade swamp as filter for acid mine drainage
Author:Clay, Soc
Publication:American Forests
Date:Jul 1, 1992
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