Reclaiming Coal-Mining Sites: Challenges in Erosion Control
Award-Winning Reclamation in the Deep SouthHydroseeding at West Virginia coal-mine siteThe federal Office of Surface Mining (OSM), part of the US Department of the Interior, provides oversight for all mining and reclamation activity supervised by state agencies. Each year, the OSM recognizes “Excellence in Surface Mining Reclamation,” and Alabama’s Drummond Coal Company received this distinction in 2000 for reclamation activity on its Arkadelphia mine site, a surface mining operation about 50 mi. northwest of Birmingham. Mining at the site began in the mid-1960s, and extraction of reserves available through surface mining was completed in 1995. Dwight Hicks, manager of permitting and regulatory compliance at Drummond, describes the premium-grade Arkadelphia reserves as “a single seam [that was] a nominal 18 inches thick and covered largely by 60 to 70 feet of hard sandstone.” The pre-mine uses of the Arkadelphia mine site were pasturage, grazing land, hay land, and some agriculture. Drummond decided to remove the good-quality topsoil on the site, stockpile it, and replace it after grading at the site was completed. Topsoil stockpiling and replacement are now regulated by federal reclamation law, but Drummond was charting new waters with this program at Arkadelphia in the mid-1970s. “Our reclamation plan called for removal and replacement of a minimum of 1 foot of soil material,” says Hicks. Any trees on the site at the time of initial disturbance were windrowed at the bottom of slopes to help control erosion. Drummond implemented an innovative “stairstep” approach to coordinating mining and reclamation efforts. Initially topsoil was stockpiled as it was removed, but once mining was completed at a portion of the site, that area was immediately graded and the topsoil replaced, while mining continued elsewhere along the coal seam. The approach proved both cost-effective and time-effective for Drummond. “As soon as we could get grading finished, put down topsoil, [and] establish drainage control, we could get vegetation established more quickly,” explains Hicks. “That’s when we would start our bond liability period. It was a rather coordinated set of events–highly orchestrated, efficient, and effective.”Early in the reclamation effort at Arkadelphia, Drummond established a cropping system on reclaimed acres to harvest viable seed for further revegetation. Drummond contracted with an independent farmer to produce the seed for the company, primarily Sericea lespedeza, an aggressive legume species. The seed was returned to the reclamation seed blend used on the next segment at Arkadelphia or was included in blends for Drummond’s other mines. In the 20 years that Drummond has maintained the seed production program, Hicks estimates that it “harvested, reclaimed, and reutilized” several hundred thousands of pounds of clean seed. Revegetation takes place at Arkadelphia during two seasons, March to June and September to late November or early December. Drummond has developed specific reclamation seed blends: cool-season and warm-season blends and special high- and low-pH blends, as soil conditions demand. Sericea lespedeza is included in all reclamation blends. “It’s a long-term legume,” explains Hicks. “It’s a soil builder and it has a deep root system, so it has the staying power to see us through that five years or more of bond liability.” Drummond’s warm-season seed blends include extensive Bermuda grass and Pensacola Bahia grass and, for quick cover and erosion control, a species such as browntop millet. Kentucky 31 fescue is a common grass in cool-season blends. Revegetation blends are normally applied at a rate of 100 lb./ac. and include a minimum of five different legumes and grasses. In addition to Sericea lespedeza, common legumes include clovers–particularly crimson clover–and alfalfa varieties. Warm-season seed is scarified, or hulled, so that it breaks dormancy very quickly. Hydroseeding at Arkadelphia was primarily employed on smaller acreages, as the accessible terrain on the site allowed for the use of conventional farming equipment.With revegetation, Drummond applies a balanced fertilizer such as Triple 13, at a usual rate of 700 lb./ac. Because Alabama topsoils are acidic, reclaimed topsoil typically receives agricultural lime applications of 3-5 tons/ac. On very acidic areas, Drummond has applied as much as 25-30 tons of agricultural lime per acre.Revegetation at Arkadelphia was considered the primary means of establishing erosion control. “Once we would put topsoil on the big acreage–the flatter areas–erosion control would come through quick establishment of vegetation: seeding, fertilizing, and lime application,” Hicks explains. “Then we would come back in and put hay mulch on top of everything.” Hay is applied at a rate of 4,000-4,500 lb./ac. Additional erosion control measures were sometimes needed at Arkadelphia. “Because we were replacing topsoil on graded overburden, on somewhat rolling terrain,” says Hicks, “we had to develop a strong erosion control set of practices and guidelines.” Diversions and terraces were heavily implemented on slopes, including many riprapped and rocked downdrains. Sediment ponds were another control measure. “We had a very extensive set of sediment ponds that would be put in for our point-source outfalls: If we had any sediment coming off a site, it would be captured before it would go to any receiving stream.” Sediment ponds are designed to retain water long enough to allow solids in the water to settle out. Erosion control measures were taken on the site simultaneously with seeding, with terraces, diversions, berms, and channels revegetated along with the rest of the area being seeded.Hicks considers maintaining water quality according to extensive water-quality regulations to be one of the largest challenges of mining reclamation. “That’s one of the reasons you have to have good erosion control. You must have a good vegetation program, to get these areas stabilized and get a vegetative cover back over them as quickly as possible. That is the main way you maintain water quality.” Drought conditions can prove devastating to revegetation, although Hicks believes that drought stress can be overcome somewhat by implementing quality reclamation and vegetation measures initially. “That’s where, for us, the application of hay mulch is so critical. That not only helps control erosion, it also helps hold moisture; it cuts down on moisture depletion until you get vegetation established.”As the first land to be reclaimed on the Arkadelphia site began to mature, Drummond looked beyond seed production to commercial forestry. “We replanted trees–loblolly pines–for commercial use,” explains Hicks, noting that effective timber production was a prime consideration for the OSM award Drummond received in 2000. The timber is managed directly by the coal company. Some small forested areas have been sold, including a site that has been turned into a golf course. Another postmining use on the mine site is primarily industrial, a quarry operation that leases the property from Drummond. Sandstone rock that was part of the overburden material is sold commercially for aggregate used in road construction. The postmining land uses at the reclaimed areas of the Arkadelphia mine site thus range from industrial/commercial to pastureland for cattle, commercial timber land, and recreational use.Hicks emphasizes the importance of carrying out effective reclamation and establishing long-term erosion control, in terms of both environmental standards and corporate benefit. “We have stringent standards that we have to meet; it’s important environmentally. On the other hand, since we have this responsibility for bonding and reclamation, we have all that money–for Drummond, millions of dollars–that can be outstanding in bond liability at any period of time. It behooves us to put together a program that’s going to control erosion, reestablish vegetation, and get through our bond liability period as quickly as possible, so that bond money can be applied to other operations.”A Regulatory Point of ViewWest Virginia coal-mine siteRichard Davis is a reclamation inspector with the Virginia Department of Mines, Minerals, and Energy (DMME), in the Division of Mined Land Reclamation. The division’s four units are responsible for enforcing coal-mining reclamation regulations and for reclaiming AML. Davis initiates AML reclamation projects, inspects existing projects, and manages an inventory of AML properties throughout Virginia. The AML reclamation program is funded nationwide through grants from the OSM, with funds derived through fees collected on coal production in active mines. Davis explains that the actual reclamation work is performed by contractors who earn the jobs through competitive bids and that he works directly with these contractors. Coal mining in Virginia takes place almost exclusively in the southwest corner of the state, in rugged habitats similar to those found in southern West Virginia. AML project sites handled by the Division of Mined Land Reclamation have been as small as 100 ft.2–a former deep-mine portal in a front yard–and as large as 30-40 ac. on a surface-mined area. AML projects in Virginia generally seek to create postmining land uses of unmanaged forest or hay-land pasture, according to the wishes of the landowner. The AML unit maintains standard specifications for seed mixes depending on the intended land use. For example, on a project with a postmining land use of unmanaged forest, Davis says they’re using grasses and legumes that aren’t particularly aggressive in their growth habitat. He explains that such varieties are more complementary to tree species. Timing of tree planting is also considered critical. “On an abandoned mine land project, we try to get the trees out just as soon as we can after hydroseeding.” Doing so helps with erosion control and tree establishment and finishes up contracts on the site sooner. Trees chosen for unmanaged forest sites–including northern red oaks, white pines, sawtooth oaks, Chinese chestnuts, and black locusts–are often selected for their benefit to wildlife species. Revegetation contractors on AML are required to inoculate legume seeds with bacteria so the legumes can incorporate the bacteria and begin the process of nitrogen fixation. “The soils we normally have on the surface might not have the native bacteria,” says Davis. To further enhance nitrogen fixation and improve other soil properties, the AML section is starting to use mycorrhizal tree seedlings, which should be better suited for these harsh environments. Davis explains that “the mycorrhizal seedling has a fungus component at the root, [so] it is much better able to absorb water and nutrients” than are other seedlings.Davis’ group is encouraged by other state and federal agencies to use native species on AML sites. The AML unit is entering into a research project with the Powell River Project–a cooperative program run by Virginia Tech, industries in southwestern Virginia, and other organizations serving the Virginia coal-mining region–to investigate establishing native, warm-season grasses on such areas. The emphasis of such an approach is to encourage natural ecological succession. “Species that we are using now might be a mix of native and non-native species, but these are nonaggressive species,” explains Davis. “Over the past year or so we have gotten away from using species that are very aggressive, like Kentucky 31 fescue, Sericea lespedeza, and crown vetch, because they tend to inhibit ecological succession.” The AML sites in southwest Virginia are very steep, with low-pH, low-fertility soils. “The topsoil has long since been buried or washed away,” Davis explains. “Often there is very little soil material there at all and lots of unweathered rock.” Using soil amendments to create a suitable topsoil substitute is more common than bringing in topsoil. After the soil has been tested, lime is applied to raise soil pH to around 5.5. The soil is further amended with fertilizer, usually 16-27-14, typically applied at 500 lb./ac. When a contractor chooses to hydroseed, such as on steep slopes, lime is applied in the mix, but Davis’ group encourages contractors to spread lime separately where possible and incorporate it into the soil. Contractors use whatever hydroseeding equipment they prefer. Often the primary contractor will subcontract out the revegetation aspect of reclamation. Site preparation involves grading–running track equipment such as bulldozers over the site–according to specifications of the reclamation plan. As in West Virginia, site access can be a problem, and hydroseeding contractors might need to hook up lengths of hose to reach their sites. As at Drummond’s Arkadelphia mine, Davis and the DMME rely heavily on revegetation for erosion control on AML sites. “Sometimes this calls for contractors to do a temporary seeding,” Davis explains. “We would use an annual species, something that’s going to grow and produce some cover very quickly. Then we would follow up with our permanent seeding.” Sediment control structures sometimes installed at AML sites include hay bales, straw-bale barriers, and silt or sediment fences. Rock check dams constructed at some sites impound small amounts of water for a very short time, allowing the water to drain through while slowing it down enough for particles to drop out. Silt fences, constructed of porous fabric, accomplish the same function. All of these structures are removed from a site prior to release of a reclamation contract. When AML sites are particularly difficult to revegetate, Davis’ group applies excelsior netting: The excelsior, which is left down permanently, consists of small wood fibers encased in a mesh netting that photodegrades.Davis describes the DMME’s particular concern with controlling runoff from AML sites: “A lot of our coal fields in southwest Virginia drain into the Clinch River and the Powell River, [where] there are numerous endangered species, mostly freshwater mussels. The US Fish and Wildlife Service has designated these areas as critical habitats, so we’re especially concerned with controlling erosion of our abandoned mine lands.” Davis is enthusiastic about a trend in Virginia’s AML reclamation that involves wetland areas. “Whenever we have a project around a wetland, we tailor our seed mix to the wetland areas, rather than use our upland seed mix.” Reclamation is believed to be enhanced by wetland development because, according to Davis, “Wetlands provide habitat for lots of wildlife species, they serve to clean the water, [and they] absorb water and release it over a longer period of time, so they sort of act as flood control.” Developing WetlandsThe importance of wetlands to AML sites has also been a focus of the Powell River Project. Directed by Carl Zipper of Virginia Tech, the Powell River Project’s mission is to carry out research and education programs that facilitate mine land reclamation and benefit both businesses and communities in Virginia’s coal-mining regions. Rob Atkinson, associate professor of biology, chemistry, and environmental science at Christopher Newport University in Newport News, VA, has devoted a great deal of research effort, through the Powell River Project, to determining the benefits of wetlands on surface-mined land. On many surface-mined sites in southwest Virginia, small depressions, formed when landscapes were altered by mining, have over the years developed characteristics of wetlands. Atkinson has evaluated many of these depressions on AML sites. He not only shares a belief in the benefits of these wetland areas, citing evidence of the many ecological services they provide, but he also advocates deliberately constructing small wetlands on AML sites to provide these beneficial functions. Constructed wetlands could assist in erosion control, trapping sediment and preventing runoff, and unlike sediment ponds, the wetlands would not be removed upon completion of permitted reclamation. Atkinson explains that the wetlands could be constructed during site preparation and grading and that hydroseeding or other revegetation could take place as they normally would. “If you have a 100-acre site, you would probably end up with an acre of wetland. You would hydroseed the whole 100 acres.” He explains that wetland areas enhance the diversity of vegetation that develops. “You have an ecological battle going on between upland plants and wetland plants. You get zonation in response to that. You get various zones within the wetlands and various zones adjacent to the wetlands, and that’s good for wildlife.” Atkinson admits that coal companies and landowners are wary of the potential problems associated with wetland construction, including liability associated with risks such as accidental drowning, and potential regulatory restrictions on the wetlands, as required by the Clean Water Act. He promotes developing very shallow wetlands, to avoid risks as well as to mimic such natural wetland areas as beaver ponds, and believes that keeping the wetlands very small might eliminate them from inclusion under wetlands regulations.A Different ApproachAn unusual approach to mine land restoration is being explored by the Bureau of Land Management (BLM) in northeast Oregon. BLM and the Oregon Department of Geology and Mineral Industries are experimenting with using cattle to improve soil quality on the site of an abandoned gold mine near Baker City. Cattle are fed in small, fenced lots, and feed, wastes, and native seed are incorporated into the soil through “hoof action.” Increased organic material and microbial activity should enhance revegetation efforts. After two years of monitoring soil structure, vegetative species diversity, cover, and invasion of noxious weeds, BLM Surface Protection Specialist Kata Bulinski says that site restoration has benefited from what she and her coworkers call the “cowmpost” treatment.ConclusionThe variety of approaches to mine site reclamation described in this article range from the tried and true to the cutting edge. All have their place as managers, reclamation contractors, and scientists balance environmental regulations, business considerations, and scientific innovation to create solutions to individual reclamation challenges.