Coal Resources Available for Development - A Methodology and Pilot Study
By Jane R. Eggleston1, M.
Devereux Carter1, and James C. Cobb2
1U.S. Geological Survey, Reston, VA 20192, 2Kentucky Geological Survey, Lexington, KY.
MATEWAN QUADRANGLE PILOT STUDY
Once a methodology had been developed for assessing available coal resources, a pilot study was conducted to apply and test this methodology. The study was a cooperative effort between the USGS and the KGS. The central Appalachian region, which includes Eastern Kentucky, was chosen as a focal point because coal production has been historically high for this region and industry has a great deal of interest in this area. The 7.5-minute quadrangle was determined to be the optimum size for study, and the Matewan quadrangle (fig. 4) was selected for several reasons. Located on the Eastern edge of Pike County, Ky., this quadrangle is fairly representative of its surrounding area, having low population density, many coal beds, and intensive mining. The quadrangle was selected also because most of its surface and underground mine maps already had been compiled.
The geology of the Matewan quadrangle has been studied by a number of researchers. Key reports used in developing the coal geology for this pilot study included the 1:24,000-scale geologic quadrangle map by Trent (1965), KGS's Energy Resources Series (Brant and others, 1983), and coal thickness (Kentucky Geological Survey, 1986) and coal quality (Currens, 1986; Currens and others, 1987) reports. KGS geologists identified 21 coal beds as being potentially minable. Of the 21 beds, some had more data available than others. The amount of data available is usually related to the degree to which coals have been economically important. Eight of the coal beds have been mined underground to some extent, and eight have been surface mined. All of the coal beds considered in this study are from the Pennsylvanian Breathitt Formation (fig. 5). The topography of the area is rugged and steep, typical of the central Appalachian region. Consequently, most of the coal beds are exposed at the surface and thus are accessible for surface and underground mining.
Abandoned and active underground mines were located and plotted in a cooperative effort between the Kentucky Department of Mines and Minerals (KDMM) and the KGS. Mined areas were located and plotted on the Matewan quadrangle, with mined coal beds being noted. In some cases, the mining companies had given coal beds names that were different from the accepted KGS bed nomenclature; therefore, an effort was made to properly correlate the mined beds with the KGS nomenclature. The mines were located with the help of records from the KDMM and the Kentucky Division of Surface Mining, aerial photography, and verbal communications with mine operators and regulatory officials. These mines were also identified as to the coal bed mined.
KGS and USGS geologists met with many local regulators, mining engineers, and consultants to determine the restrictive parameters that should be applied to the Matewan quadrangle. Some of the land-use restrictions were outlined under the Kentucky Natural Resources and Environmental Protection Cabinet Document 405 KAR 24:040, entitled "Permit Application Review," and the Kentucky Revised Statutes 350.465 and 350.610, which define Kentucky's surface mining regulatory program. Also, the Lexington regional office of the OSM was helpful in describing potential variances to regulations and their likelihood of being granted. If the granting of a particular variance is commonplace, the restriction was not considered in this study. In addition, information pertaining to potential nonregulatory restrictions (for example, powerlines or pipelines) and depth and thickness limits of a coal bed was obtained from State agencies including the Kentucky Natural Resources and Environmental Protection Cabinet, the Kentucky Department for Surface Mining Reclamation and Enforcement, and the KDMM.
Computer methods were used to enter, store, generate, and manipulate the information concerning thousands of minute locations and to perform the repetitive combinations and calculations involved in the project. The USGS has developed the National Coal Resources Data System (NCRDS) as the master data base for coal resource information. NCRDS maintains a data base manager (PACER) (Cargill and others, 1976) and graphics programs (GARNET) (Olson, 1977) to access and manipulate the data for coal resources assessment. GARNET programs calculate and tabulate coal resources according to the specifications of USGS Circular 891. Therefore, the NCRDS formats and software were selected for the coal availability studies.
Data for the Matewan quadrangle were compiled during a recent coal resource assessment study (Brant and others, 1983) and were transfer to the NCRDS format and data base with ease. KGS geologists digitized coal outcrops of the 21 beds identified for study and digitized the mine map data acquired from the KDMM.
Four of the land-use restrictions (powerlines, pipelines, streams, and towns) were plotted on scale-stable base maps and digitized by the KGS. Cemeteries and oil and gas wells were digitized as points, and GARNET created the buffers around them. All of the boundary lines for technological restrictions were generated by GARNET. The restrictions applied to the Matewan quadrangle are as follows:
|100-ft buffer (a GARNET-generated 300-ft by 300-ft square around center of cemetery was used).|
|Oil and gas wells||a 200-ft by 200-ft square around well site was used.|
|Major streams||100-ft buffer if flow greater than 5 cu ft/S.|
|Too thin||less than 14 in is resource cutoff.|
|Too deep||greater than 200 ft.|
|Too thin||less than 28 in.|
|Too deep||greater than 1,000 ft.|
|Deep mine barrier pillars (between mines, for safety||
50-ft buffer zone around active or abandoned mines.
|Deep mining too close above or below||less than 40 ft of separation.|
|Thicker beds too close above or below||less than 40 ft of separation.|
|Oil and gas wells||200-ft by 200-ft square around well site.|
A conflict appeared in reporting potential overlapping land-use and technological restrictions in the 0- to 200-ft overburden category. For this study, the decision was made that future mining at less than 200 ft of overburden was most likely to be surface mining, so that only those restrictions applicable to surface mining were applied to the 0- to 200-ft category.
After all of the Matewan data were transmitted to the USGS and entered into NCRDS, all computer searches, manipulations, combinations, resource calculations, and tabulations were performed by the USGS in close communication with the KGS. USGS personnel ran computer programs to test and develop the methodology and applicability of NCRDS software to parameters for a coal availability study. In fact, methodologies were modified and GARNET and other NCRDS programs were enhanced frequently as the project progressed.
PACER searches of the stratigraphic data base extracted only the coal within each coal bed, excluding partings and other noncoal lithologies. Coal thickness and elevation files were created for each of the 21 coal beds. The data points were displayed and gridded, and isopach and structure contour lines were plotted. Where necessary, interpretive points were added and incomplete coal thickness data deleted to derive reasonable coal thickness and structure depictions. The 14- and 28-in isopach lines were stored as boundary lines for coal thickness. The bed elevation grids were stored for subsequent combination with a grid file of the surface topography to derive overburden and for grid-to-grid operations to calculate interburden intervals between the coal beds.
The DEM for the Matewan 7.5-minute quadrangle was acquired from the National Mapping Division of the USGS. This model provided a grid with 60-m spacing of the surface elevations that, when combined with the top-of-coal elevation grid for each coal bed, supplied the overburden categories (200 and 1,000 ft) required as overburden criteria for each coal bed.
A grid interval of 0.03728 mi (approximately 43,000 grid nodes in the Matewan quadrangle) was selected for use in resource calculation and is recommended for future coal availability studies. This interval corresponds to the 60-m (approximately 200-ft) grids of the DEM's as utilized in GARNET. The GARNET resource program subdivides each grid cell into 16 segments. A 200-ft grid interval is thereby subdivided into 50-ft squares to ensure that the smallest boundaries (the 50-ft barrier pillars) would not be excluded from the resource computations.
GARNET programs generated the combinations of coal thickness lines (isopachs), overburden and interburden lines, outcrops, surface and underground mines, and each of the land-use and technological restrictions. Several thousand different combined areas were created, and more than 1,000 were used in coal resource calculations.
Original coal resources, coal mined and lost in mining, remaining coal resources, individual restrictions, and available coal resources were all calculated as a check on the methodology. However, only two of the first three and one of the last two must be calculated, so we recommend that coal mined and lost in mining, coal remaining, and individual restrictions should be calculated. The original resource may be derived from the sum of the two categories "coal mined and lost in mining" and "remaining coal resources." Available coal resources is the result when the restricted coal is subtracted from the remaining coal resources.
Enough chemical data were available in the KGS computer files to generate sulfur isopleth lines for most of the 21 beds. The amount of available coal meeting current compliance standards was then calculated for the Matewan quadrangle.
The methodology was repeated for each of the 21 coal beds. Figures 6-10 are a series of maps depicting the areas affected by restrictions on one bed, the Upper Elkhorn No. 2. Figure 6 shows the original, posterosional extent (shaded) of the Upper Elkhorn No. 2 coal bed in the Matewan quadrangle, Ky. The white area indicates an absence of this coal bed. As additional restrictions were applied to the Upper Elkhorn No. 2, more and more of the coal bed was eliminated from consideration. On figure 7, portions of the coal bed that have been removed by underground and surface mining are shown. Land-use restrictions have been added on figure 8. These include powerlines, pipelines, gas and oil wells, cemeteries, towns, and large streams, all with buffer zones around them. All of these land-use restrictions, except for oil and gas wells, apply only to surface mining. Technological restrictions affect a large portion of the Upper Elkhorn No. 2 coal, as shown on figure 9. These restrictions apply only to underground-minable coal and include (1) portions of the coal bed that lie less than 40 ft above or below an abandoned mine or a coal that we judged would be more desirable to mine, (2) deep-mine barrier pillars, (3) buffer zones around oil and gas wells, (4) areas where the coal lies more than 1,000 ft below the surface, and (5) areas where the coal is too thin (less than 28 in thick). Figures 10A and 1OB illustrate the results, after all mined and restricted coal was eliminated. Coal available for surface mining was limited to that which is less than 200 ft deep and 14 in or more thick; this available coal is shown as the shaded area in figure 1OA. Coal available for underground mining is shown as the shaded area in figure I OB. Figure 11 summarizes the results of the Upper Elkhorn No. 2 resource analysis. Of the 92 million short tons of coal remaining today in the Upper Elkhorn No. 2 coal bed, 28 million short tons (30 percent) are estimated to be available for mining, most of which is considered to be surface minable.
A similar methodology was applied to the other 20 coal beds included in the Matewan quadrangle pilot study. Results for all 21 coal beds in the quadrangle are presented in table 2. Figure 12 summarizes the results in pie-chart format, showing resource results by percentage of the original 986.5 million short tons of coal. Most of the mined coal was removed by underground mining (92 percent).
Land-use restrictions play a very minor role in limiting surface mining, restricting only 2 percent of original coal. Of the land-use restrictions considered, major streams (flow greater than 5 cu ft/S) restrict the most coal (38 percent) (table 3). Of the 23 percent of original coal restricted by technological parameters, coal beds that are too thin (less than 28 in) contribute the most to restricting coal from being mined underground (table 4). Finally, 613 short tons of coal (62 percent of original coal) in the Matewan study area are available for mining, 53 percent of which is available for underground mining and 47 percent for surface mining. If coal quality factors are considered, only 27 percent of the original coal is available for mining and meets EPA compliance standards.
Other Limiting Factors
Other factors may limit the availability of coal even further. For example, in many situations mining could be inhibited or totally restricted by localized geologic problems such as coal-bed discontinuities or mine roof problems. Economic factors may further limit coal availability. Many mine costing models incorporate financial factors to determine the amount of coal that could be mined at various costs. Agencies such as the Electric Power Research Institute (EPRI, 1981) and the U.S. Department of Energy (EIA, 1982) have developed mine costing models, as have many mining companies. These models could be applied to the results of this study to determine the impact of the economics of mining coal on the quantity of available coal that might actually be currently minable or minable at a given price.
In this study, available coal is still coal "in the ground," not the quantity of coal that actually reaches the market. Prior to shipment, coal is lost in mining and in cleaning. In general, approximately 50 percent of available coal may be lost during underground mining (depending on the mining method used), 10 percent during surface mining, and 10 percent or more during coal cleaning (when required). When these recovery factors are applied to the estimated 613 million short tons of available coal in the Matewan quadrangle, it becomes evident that a significantly smaller amount of coal will actually arrive at the market.
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