More than 18 months have passed since Martin County Coal, a subsidiary of Massey Energy, experienced one of the coal industry's worst environmental disasters in recent memory. The incident reshaped how engineers and regulators approach the design of coal refuse disposal systems. As many Appalachian mines await approvals for new systems to dispose of the waste stream from coal preparation plants, the current impoundments are running out of room.
During October 2000, a "breakthrough" occurred, near Inez, Ky., in which Martin County Coal's 72-acre refuse impoundment released approximately 250 million gallons of slurry into adjacent underground mine workings. The slurry then discharged into two tributaries of the Big Sandy River (the border between eastern Kentucky and West Virginia), flooding stream banks to a depth of 5 feet (ft). Although no one lost their life, the environmental damage was huge and local water supplies were disrupted for days. Martin County immediately began to clear the mess and now that process is largely complete, according to the company (See Operating Ideas, page 40). Last month, however, Massey Energy suffered from another small discharge (See News, page 6).
Both Kentucky and West Virginia issued notices of violation related to the major discharge and ordered remedial measures. Downstream residents and others claiming to be damaged by the spill have filed several lawsuits, which seek compensatory and punitive damages. According to a recent Massey Energy financial statement, the company took a $3 million charge in the fourth quarter of 2000 relating to the slurry spill. Of the $46.5 million the company spent to clean up the mess, the company's insurance at the time only covered $43.5 million.
This is not the first time the public has suffered from a massive discharge, nor is it the worst. In 1972, a dam at Pittston's Buffalo Creek refuse impoundment collapsed killing 125 people, injuring 1,100, and leaving more than 4,000 homeless. The coal industry has not experienced a dam failure since Buffalo Creek, but there has been one fatality associated with refuse disposal and four or five instances where slurry leaked from the impoundment pool area.
Massey Energy knew they had problems before the big discharge and they are still having problems. In 1994, Martin County had another small incident where slurry leaked from a different location with the same affect, just a much smaller amount. At that time, the Mine Safety and Health Administration (MSHA) required them to try to strengthen the pool area. They decided to push fill material above the basin to create a buffer. They had hoped that the earthen blanket would reinforce the fractured coal strata and prevent the lateral conductivity between the slurry pool and the old mine workings.
The magnitude of the incident, outraged coalfield residents, and environmentalists caught the government's attention. Congress authorized $2 million for the National Academy of Science's National Research Council (NRC) to study refuse impoundments. The study concentrated not just on the Martin County spill, but on coal waste impoundments in general. The report, Coal Waste Impoundments: Risks, Responses, and Alternatives, was released Oct. 12, 2001.
The report makes several recommendations for regulating the design, construction, and operation of refuse impoundments. It also suggests alternatives to impounding refuse, many of which are currently prohibitive from a cost standpoint. In addition to claiming that it needs to do more research, the NRC offered some design and construction alternatives that may be more realistic.
NRC RELEASES ITS FINDINGS
The Martin County incident caused Congress to request the NRC to examine ways to reduce the potential for similar accidents in the future. To conduct this study, it appointed a committee on coal waste impoundments. The charge of the committee included three major components: examine engineering practices, evaluate the accuracy of mine maps, and evaluate alternative technologies. The committee had 10 meetings between March and July 2001, eight of which included town hall meetings that were held to gain input from citizens of local communities.
The report recognized that both MSHA and the Office of Surface Mining (OSM) have language that addresses in detail the engineering and stability aspects of the embankment; however, there is little reference either to the basin area or to requirements of the engineering design for other areas of the facility. The committee recommended that both regulatory agencies have clear authority to review basin design.
It also suggested that they continue to adopt and promote the best-available technology and practices with regard to site evaluation, design, construction, and operation of the impoundments. For example, the report said that the agencies could commission periodic reviews of existing technical procedures and practices, with particular attention to the basin, and the results could be disseminated to the coal industry. Based on the outcome, the agencies might need to revise guidelines.
The group acknowledged that embankments could fail in a variety of ways. The study stipulated, however, that while continued vigilance concerning design, construction, and operation of the embankment is clearly warranted, the largest uncertainties remain in the characterization of the basin area and, therefore, in the mitigation of risks associated with the breakthrough potential.
The committee recommended that MSHA and OSM develop and promulgate guidelines for the site evaluation, design, construction, and operations of basins. It recommended that they jointly pursue the issue of outcrop coal barrier width and overburden thickness and its competencies and develop minimum standards. They also suggested that MSHA review its current practices and develop guidelines for the design of bulkheads intended to withstand hydraulic heads associated with slurry impoundments.
The key to assessing the potential for a breakthrough is knowing the extent of those underground workings with respect to the impoundment basin. The committee recommended that MSHA work with OSM and state agencies to establish standards for mine surveying and mapping. It also recommended that the agencies consider requiring additional continuous monitoring. When mine maps are unavailable or there is reason to doubt their accuracy, the committee found that additional investigation to locate underground mine workings is warranted. Realizing the time and expense associated with extensive drilling, the report suggested the use of remote sensing and geophysical methods to search for abandoned mines.
Looking at the longer-term solutions, the study suggested that mine operators look at the total system of mining, preparation, transportation, and use of coal, and the associated environmental and economic issues. Ideally, it would be in the best interest of all parties to reduce the amount of refuse. Another option might be burning the refuse.
The report also reviewed alternative methods for coal slurry disposal, which include incised ponds, slurry cells, combined refuse piles, and co-disposal of fine and coarse refuse. In many instances, these methods are influenced by topography, geology, and mining and preparation characteristics, and therefore their application is site specific.
SO, WHAT WENT WRONG?
Today, the coal industry estimates that it has 225 active impoundments (coarse-coal upstream construction dams) in the Appalachian region. "We have so few areas in the Appalachian region where mines can place a slurry impoundment because of the proximity to old works," said Steve Gardner, president of Mining Consulting Services Inc., a mining engineering firm located in Lexington, Ky. "If all of the sites were eliminated on that basis, it would have a tremendous impact on the coal mining business. We need to find ways to design around these limitations."
Editor's note: A well-respected mining engineer, Gardner was one of the engineers originally asked to be a consultant to the NRC coal waste impoundment committee because of his extensive experience with impoundments in the Appalachian region. The consultants originally named to advise the committee were eliminated after complaints from environmentalists. Gardner did provide testimony before the committee and was later an independent reviewer of the final report.
Directly after the Martin County spill, coalfield rumors led to a lively debate as to how close the mine works were with respect to the impounded area. The final MSHA report determined that the maps were accurate. The old works were, however, within 70 ft of the pool area.
"We [engineers designing refuse impoundments] did not think about pool areas causing that much of a problem," Gardner said. "When we first heard what happened at Martin County, my first thought was that the maps must have been wrong and the mine was much closer to the surface than people thought. That was not the case.
The old workings were exactly where everybody thought they were. The fracturing associated with the near surface sandstones and shales was much greater than anticipated. The weight of slurry caused them to widen and eventually fail."
Prior to the NRC study, engineers within the coal industry debated many options to treat refuse streams. These included:
Combining coarse refuse, fines, and dewatered fines and trucking them to a flat disposal area - not practical;
Using belt presses, which handle 25 to 30 tons per hour (tph) per press, to dewater the refuse stream. A 400-tph prep plant would need three presses, which is about $1 million worth of equipment. The consumable costs would be $0.25 per ton and the overall cost would be $3 per ton. This would only be a temporary fix if rain was allowed to accumulate in the basin; and
Underground injection of fines, but any undulation in the coal bed stops the fines from flowing. There is also the potential problems for working miners.
"We have been contacted by several operators wanting to talk about flyash grouting, selective drilling, building artificial pillars and bulkheads," said Al Campoli, business development manager for Fosroc. "These are all very, very expensive. The pillars near the outcrop are so small. Conditioning the mine to prevent a rapid inflow is just not cost effective."
The operators are starting to better understand the rock mechanics involved in holding water in laminated strata. Previously, Campoli explained that the mine foreman's equation was what everyone used: the barrier has to be 50-ft thick, plus 1 ft of thickness for every foot of head. "It's an empirical solution derived from experience in the 8- to 9-ft thick Pittsburgh No. 8 seam, which is a very permeable structure," Campoli said. "There really isn't very much in the way of science in designing underground barriers, let alone what is needed for the strata surrounding the opening."
All of this activity is an indication of how serious the operators are getting about this problem. "Previously we would have done the same thing Martin County did - pushing spoil material over to attempt sealing," Gardner said. "And, in 99 out of 100 cases, that would probably work, but you can't quantify that it will work."
"The problem is that the cast over is unconsolidated soil with lots of clay that is susceptible to piping flow," Campoli said. "That stuff just melts away."
NEW TECHNOLOGY: REFUSE STABILIZER
Based in Georgetown, Ky., Fosroc, a specialty mining chemical company, has been secretly working with operators to develop another alternative. They are trying to stabilize the refuse in the impoundment rather than preventing flow. "Fosroc's alternative is an off-shoot of the time-honored solution of adding copious amounts of Portland cement to stabilize the tailings permanently," Campoli said. "We have developed a stabilizer [2% by weight of the slurry] that is added at the thickener and mixes on its way to the impoundment.
"The refuse is handled the same way," Campoli said. "It provides a 25-psi unconfined compressive strength in 40 days. Something with that compressive strength will not move and it's more than self-supporting," said Campoli.
The cost to the customer depends on the characteristics of the coal, the mining technique, and the mechanical handling. "The price depends on the amount of refuse in the run of mine coal and the amount of fines," Campoli said. Speaking in round figures, Campoli explained that, assuming an 80% coal recovery with 20% fines in the waste and that the slurry has 30% solids [70% water], Fosroc estimates that this technique will cost about $0.50 per ton of clean coal.
The system requires only a small amount of water. "We believe this is an original concept and we are applying for a patent," said Peter Mills, technology leader for Fosroc. "One of the key aspects of this formula is that it's designed to let the coal company reuse the water. People have tried Portland cement before. There are a lot of problems with that. It tends to tie up all of the water in the slurry. The excess water weakens the final structure, not to mention the valuable space it takes up within the impoundment."
The dosing equipment is compatible with current technology. "We have a patent filed, but it's mostly a special kind of cement," Mills said. "It allows the water to be recycled. The binder will be designed to be compatible with flocculants in the static thickener," Mills said. "When the water is reused, existing systems will not suffer from degradation."
"Within the impoundment's basin, there are only a few selected areas that are subjected to the geotechnical risks that lead to the spill," Campoli said. "The refuse could be brought up in lifts. By conditioning only the layers that could escape into the old works, the coal company can stabilize the impoundment and prevent flow. Basically, they would essentially convert the refuse into engineered construction material."
"Martin County attempted to use a blanket of spoil pushed over from above to form a seepage barrier," Gardner said. "In the original design, there was supposed to be a layer of coal fines over the seepage barrier directed by pumping slurry in that area to seal the spoil barrier."
According to Campoli, "That type of spoil is highly susceptible to piping flow. The samples that Fosroc prepared seemed to be quite resistant to piping flow. The fines are so small that it makes for a very tight package once it has stabilized, providing for a very impermeable barrier."
"The traditional way of impounding slurry is to pump it behind the embankment to help seal the coarse refuse and the material from which the embankment is made," said Gardner. "This material could be used to help solidify and seal the pool areas, even selectively. Building up certain layers, the mine operator could use it for a limited amount of time until one was comfortable that the area was sealed and then go back to traditional slurry pumping. Throughout the design process, we also must remember that adequate drainage allowances must always be made.
"The operator might have a higher initial cost, but then they could reduce it when they were comfortable that the area was sealed," Gardner said. "In some cases the company would have to do it for a longer period of time. Those are decisions made during the design processes."
"Assuming that conventional coarse dam slurry impoundments are going to survive in Appalachia, we need increased engineering on the wing walls in the pool area," Campoli said. "The realistic solutions that have been proffered so far include building bulkheads at the edge of the pool (getting into the underground works and building engineered bulkheads), stabilization of slurry to prevent flow, and the injection of grout/slurry into old works to prevent flow."
"There's no doubt anywhere, and the National Academy report backs this up, that the dams are safe," Gardner said. "Until the Martin County incident, all of the attention of the engineers and regulators had been focused on the dams. We all now know that we need to focus more attention on the pool areas. Another result of the Martin County incident, combined with the mountaintop mining and fill debate, is a requirement from regulators for operators to perform an alternatives analysis to justify the slurry impoundments."
Albeit costly, mishaps such as this tend to ultimately improve the overall safety of an industry. The subsequent refuse impoundments that have been proposed since this spill occurred have been designed with Martin County in mind. They will be better researched and engineered. In addition, some new solutions, such as refuse stabilizers, are being developed to help mines raise the safety factor.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Martin County Coal accident, design recommendations for coal refuse dispo|
|Comment:||Design Alternatives.(Martin County Coal accident, design recommendations for coal refuse dispo)|
|Publication:||Coal Age (1996)|
|Date:||May 1, 2002|
|Previous Article:||USGS ASSESSMENT: COMPLEX FUTURE FOR APPALACHIAN COAL.|
|Next Article:||Panel Gives Green Light to Coal Venture.|