Coal in Indiana: Reconnaissance of Coal-Slurry Deposits in Indiana
  

by:
Denver Harper, Chris Dintaman, Maria Mastalerz, and Sally Letsinger

INTRODUCTION

Indiana has a long history of coal mining by both underground and surface methods, and the state is still a major producer of coal (34.5 million tons in 2005, Indiana Coal Council). Since the late 1920s, many coal operators in the state have found it necessary to prepare their coal for market by using increasingly sophisticated equipment to size and clean their product. Reject from these preparation facilities can be broadly characterized as "coarse-grained refuse" (also known as "gob") and "fine-grained refuse" ("tailings" or "slurry"). Deposits of the latter type are referred to here as "coal-slurry deposits" or "CSDs."

In addition to mineral matter and water, CSDs contain significant quantities of fine-grained coal. Since the 1930s, as energy prices have fluctuated and coal-preparation technology has advanced, attempts have been made intermittently to recover the coal in CSDs in an economically feasible manner. Although such recovery has been successfully achieved at a few sites, many CSDs--including some very large individual deposits--remain scattered across southwestern Indiana. Because CSDs also contain significant quantities of pyrite, they are a source of acidic mine drainage. Since 1977, coal operators have been required to reclaim their CSDs by establishing vegetation, and most CSDs that were created before that date have been reclaimed by the Indiana Division of Reclamation with funding from the Abandoned Mine Lands Program.

CSDs were emplaced in a variety of settings, including impoundments behind berms and in dammed valleys, and in final-cut pits, haul roads, and spoil deposits of surface mines. Emplacement typically occurred over a period of years or decades and significant internal variations in mineralogical, chemical, and textural characteristics exist within the deposits. Knowledge of such variations is important in any attempt to recovery slurry from a CSD in an economic and environmentally responsible manner.

The primary purpose of this reconnaissance investigation was to identify and map CSDs and estimate the volumes of slurry in each deposit. The approximate locations of preparation plants and associated CSDs in Indiana were determined from an extensive review of the mining and geological literature. Using techniques of geographic information systems (GIS), exact locations of preparation plants and changes in the configuration of CSDs through time were then mapped from georeferenced historical aerial photographs and other aerial imagery. These efforts resulted in the production of Environmental Systems Research Institute, Inc. (ESRI) ArcMap shapefiles showing the locations of coal-preparation plants and extents of coal-slurry deposits. GIS techniques were then used to determine the area of each deposit. Assumptions were made regarding the thicknesses of CSDs that were emplaced in various types of settings, and estimates of thickness were made using information from the National Coal Resource Data System (NCRDS), the Coal Mine Information System (CMIS), and digital line graphs (DLGs) of the U.S. Geological Survey. The volumes of CSDs were then calculated using GIS.

A secondary purpose of the investigation was to collect, compile, and analyze records of chemical analyses of slurry performed in the 1970s and 1980s that are contained in the archives of the Indiana Geological Survey. These efforts resulted in the production of a Microsoft Excel spreadsheet that contains chemical analyses for 473 individual samples, as well as average values calculated for various mine sites. Statistical analyses were performed to identify vertical trends among individual samples within drill holes, as well as lateral trends for average values from drill holes within various CSDs.

This investigation was a cooperative project of the Indiana Geological Survey, R.E. Mourdock and Associates, LLC., and Purdue University Calumet. Funding was provided by the Center for Coal Technology Research, Purdue University, West Lafayette, Indiana.

BACKGROUND

Historical Development
After 1924, in response to a variety of competitive market conditions, coal production from Indiana began a rapid decline that lasted through the 1930s. Coal operators attempted to reverse this decline by adopting labor-saving technologies, including the introduction of mechanical loading machines in underground mines and increased use of surface mining. However, both these developments further degraded the quality of the raw coal that was being produced, the reputation of which had long suffered in comparison with coals from the Appalachian Basin. The operators addressed these quality problems by adopting coal-preparation technology in the late 1920s, a trend which accelerated in the 1930s.

Prior to the 1920s, coal preparation consisted primarily of crushing and screening the raw coal into several different size fractions, referred to by descriptive terms such as "lump," "egg," "nut," and "screenings" (in decreasing order of size). The largest sizes were in greatest demand and commanded the highest prices. At some coal-preparation facilities, employees (referred to as "pickers") removed visible impurities from the larger fractions by hand. After the late 1920s, increased reliance was placed on mechanical preparation of the coal--utilizing both dry and wet techniques--through the use of air tables and vibrating screens, jigs, washing tables and hydroseparators, and dryers to remove impurities and increase the number of marketable size-fractions (Coal Age, 1936a, p. 192; 1936c, p. 501; 1938b, p. 96, 99, 101). By 1937, about 1.6 million tons of Indiana coal was "washed" (out of a total production of 16.4 million tons), and an article in Coal Age (1938a, p. 42) noted: "To market an otherwise unmerchantable coal, particularly in the industrial sizes--namely, 2 in. or less--the coal-mining industry in Indiana has installed a number of washing plants. During the NRA [1933 to 1935], there were two mines in the State equipped to wash coal. Today there is a total of eleven plants washing coals from fifteen mines."

Throughout the 1930s and 1940s, the increasingly widespread adoption of coal stokers by all types of coal consumers was another powerful market force that accelerated the adoption of advanced preparation technology (Coal Age, 1948, January, p. 58-63).

Coal preparation became ever more elaborate and resulted in the need to dispose of ever larger quantities of rejected material. Because coal-preparation methods are imperfect, the reject invariably contains some coal, and by 1936, a combustion engineer with a coal company was making the following observations at a meeting of the Indiana Coal Mining Institute (Coal Age, 1936b, p. 303): "...a progressive operator must have twelve to fifteen individual sizes, not counting combinations, to meet the market demands. Loss of slurry or fines in washeries... is a step in the march of progress and eventually some method of utilization will be found."

Whenever possible, coal operators attempted to utilize the finest sizes (referred to as "slack," "dust," or "carbon"), either by mixing it with coarser saleable material, by burning it at the mine site to fuel steam plants or electrical generators, or by selling it to other industries. As noted in an article about the Talleydale Mine (Coal Age, 1936c, p. 501): "Dust, when marketable, constitutes a sixth size (minus 48-mesh); otherwise, it is run to the refuse." At the Sunspot Mine, the finest material was mixed with coarser sizes and sold (Coal Age, 1955a): "…minus 1/4-in carbon, is transported…for loading with 1 1/4 x 1/4, as desired." Reject from preparation plants was the primary fuel for the Antioch power plant, which served the Friar Tuck and other nearby mines (Coal Age, 1937a), as well as for on-site power plants at the Dresser Mine, the Kings Station Mine, and the Saxton Mine (Coal Age, 1926, 1934, and 1944, respectively).

Depending upon the configuration of the preparation plant, the material that was rejected as waste in the form of slurry was typically characterized as being less than 3/16-inch in diameter, and, at several facilities, less than 48 mesh (0.015-inch). Published estimates of the total amount of reject (including both coarse- and fine-grained refuse) ranged from 4 to 15 percent of plant input (Coal Age, 1936a and 1936c, respectively).

From the 1950s to the present, engineers have continued to develop coal-preparation technology with the objectives of maximizing removal of ash, pyrite, and trace elements--as well as the recovery of fine coal--at reduced operating costs. By 2000, when total coal production from Indiana was 25.3 million tons, there were 19 preparation plants operating in Indiana and CSDs were still being actively created (Fiscor and Lyles, 2004).

Because CSDs contain large quantities of pyrite, acidic soil conditions are generated in the unsaturated zone of such deposits where the slurry is exposed to the atmosphere, and unreclaimed deposits typically remain barren of vegetation for decades, until all the pyrite becomes oxidized. After passage of the Surface Mining Control and Reclamation Act (SMCRA) in 1977, mine operators were required to reclaim their CSDs after mining terminated, and the Abandoned Mine Lands (AML) program was instituted to reclaim abandoned CSDs. Most of the abandoned deposits have since been revegetated after being covered by a cap of soil, synthetic soil, or spoil, or following application of large quantities of agricultural limestone ("direct revegetation").

Figure 1. Photograph of the Minnehaha coal-slurry deposit (ID_IGS: D3) showing its bounding berm. The photograph was taken in 1954 (Photo ID: QO-1N-113) and has been altered to enhance contrast. The width of the area shown in the photograph is approximately 950 m.

In the early 1970s, color-infrared Earth Resources Technology Satellite (ERTS) imagery (scale, 1:120,000) taken in May 1971 was used to map CSDs, and the total acreage of such deposits in Indiana was estimated to be 1,631 acres (Wobber and others, 1974, 1975). In the late 1970s there were two significant reconnaissance investigations that involved the mapping of CSDs in Indiana. Weismiller and Mroczynski (1978) provided maps showing areas of CSDs, as well as areas of gob deposits (namely, coarse-grained refuse from coal preparation). Using color infrared aerial photographs taken in the early summer of 1971 and techniques of remote sensing, they mapped 242 polygons, of which 29 are designated as being CSDs. Personnel of the Indiana Department of Natural Resources, Division of Reclamation, subsequently made site visits to verify the interpretations. Eggert (1979) provided a map showing the point locations of 44 CSDs and active preparation plants. He described site conditions of the CSDs and provided tabulated information about each site, including mine names, active dates, coal beds mined, total production, and so on.

Slurry Emplacement

Fine-grained refuse in the form of slurry was removed from coal-preparation plants through pipelines. The point at which the slurry emerged from the pipe and entered a disposal cell is referred to alternatively as the "discharge point" of the pipe or the "entry point" of the disposal cell. At underground mines, disposal cells were specially constructed, but at many surface mines, preexisting features such as final-cut pits, inclined haul roads, and spoil deposits were utilized for slurry disposal.

Disposal cells sometimes consisted of impoundments ("slurry ponds") that were bounded by berms constructed of gob or spoil (disturbed and displaced overburden from surface mining) (fig. 1).

A description of the construction of such a slurry pond at a mine in southern Illinois, where the slurry was subsequently re-mined and sold, is provided in an article in Coal Age (1950a, p. 85): The sludge pond is built up gradually over a period of years by continually building one levee on top of another. To start the pond [the slurry-plant superintendent] first laid down an 8- to 10-ft levee of clay on three sides of a 1,000-ft square area. The levee on the fourth side of the square-the south side-was built of gob. The discharge end of the slurry pipe was mounted at the northwest corner of the square and the slurry then was pumped in. Water draining down through the slurry could not pass through the clay levees, but did seep through the gob levee, and finally into a make-up water reservoir. From there the water was recirculated to the preparation plant.

When the slurry neared the top of the original four-sided levee, another levee was built on top. The new levee was made of gob on all four sides. Slurry continued to enter the sludge pond, but the water seeping down through the slurry still could not escape through the bottom clay levee on three sides. It did filter through the original gob levee, however, and continued, as before, to flow into the reservoir. Thus adding one levee on top of another, Peabody has been able to build the sludge pond up to almost any desired depth. The pond now being mined is some 50 ft deep.

At some surface-mine operations, final-cut pits were used as disposal cells (fig. 2). Within active surface mines, coal is typically trucked out of active pits on haul roads. These haul roads, or the remnants of haul roads, were sometimes subsequently used for disposal of coal slurry after active mining had ceased.

Spoil deposits were also utilized as disposal cells at some surface-mine operations. Slurry flowed through the troughs between steep-sided spoil ridges; as a trough became filled, the slurry would overflow through notches in the ridges into adjacent troughs (fig. 3). Water would percolate down through the spoil, leaving a dry surface that could later be reclaimed.

Figure 3. Photographs of the Chieftain coal-slurry deposit (ID_IGS: B9) in 1946 (left) and 1954 (right) showing the infilling of troughs within a spoil deposit with slurry. By 1954, the spoil ridges were already being revegetated with trees. The photographs (Photo IDs: GN-2D-008 and GN-1N-096) have been altered to enhance brightness and contrast. The width of the area shown in each photograph is approximately 400 m.
Figure 2. Photograph of the Airline coal-slurry deposit (ID_IGS: E3), where a final-cut pit was used for slurry disposal. The photograph was taken in 1949 (Photo ID: QP-3F-122). This coal-slurry deposit was studied by Eggert and others (1980). The width of the area shown in the photograph is approximately 1,000 m.


Internal Characteristics

From the 1970s through the middle 1980s, personnel of the Indiana Geological Survey (IGS) conducted a program of mapping, sampling, and analyzing deposits of gob and slurry. A total of 519 samples was collected from CSDs and analyzed by IGS personnel (Miller and Eggert, 1982, p. 50). Some washability tests and grain-size analyses were performed in addition to chemical analyses, such as proximate and ultimate analyses. The samples were obtained from 93 different drill holes associated with 14 coal-waste areas. Using these data, Eggert and others (1980) provided a detailed characterization of coal slurry at the Airline-Sponsler Mine, while Eggert and others (1981) described CSDs associated with the Green Valley Mine. Based upon the entire sample set, Miller and Eggert (1982) estimated that the total tonnage of CSDs in Indiana at that time was about 40 to 50 million tons distributed across 1,400 acres, which they estimated to represent about 20 million tons of recoverable coal. Some additional samples were collected and analyzed in the middle 1980s.

Complex internal variations in the mineralogical, chemical, and textural characteristics of CSDs have been demonstrated to exist. At a CSD in southern Illinois where slurry was mined and sold, the mine officials made the following observations (Coal Age, 1950a, p. 85): In planning the sludge recovery, [the slurry-plant superintendent] and other Peabody officials figured this way: the high-ash slurry would settle out nearest the discharge end of the sludge pipe and ash content would fall in proportion to the distance from the discharge. Thus ash content of the coal in any area of the sludge pond could be predicted with reasonable accuracy. They also figured that the slurry farthest from the discharge would be the very smallest size and that, for that reason, it could not be dried without added cost.

They were right on all counts. That's why the sludge pond is "mined" no closer than 100 ft or so to the discharge point and no closer than 200 ft or so to the…farthest corner of the pond. "Mining" thus is confined to the center area of the pond, where ash content and moisture are marketable.

A more scientific approach was taken by Eggert and others (1980), who investigated a slurry deposit that had been emplaced in a long (3,000-m), narrow (80-m) final-cut pit at the Airline-Sponsler Mine, Greene County, Indiana. They described the sediments in the deposit as a "manmade prograding fan-delta system" in which there were vertical and lateral sequences of sediments whose physical characteristics were predictable (Eggert and others, 1980, p. 255) (fig. 4).

Figure 4. Schematic diagram illustrating the distribution of particle sizes in a disposal cell.

As the slurry emerged from its discharge pipe, its fluid velocity was suddenly reduced, resulting in the deposition of large pieces of coal, coal minerals, rock fragments, and sulfide-mineralized coal that were high in ash and sulfur and possessed low calorific value (Eggert and others, 1980, p. 259-260). As the slurry flowed across the subaerial portion of the deposit, the remaining coarse tailings were deposited. When the slurry reached the standing water of a pond, its fluid velocity dropped sharply and only clay and ultrafine coal remained in suspension, gradually settling to the bottom. Eggert and others (1980, p. 258) estimated that the particle sizes of about half the deposit were less than 140 mesh (0.0965--0.1067 mm) and noted that such small sizes absorb large amounts of moisture and cause significant material-handling problems.

The slurry deposit investigated by Eggert and others (1980) had a single entry point and a simple geometry. Physical characteristics of deposits are much less predictable where the geometries of the cells are more complex or where multiple entry points may have existed. As described in a later section of this report, development of the Chinook CSD was particularly complex. Initially, slurry was disposed of in a final-cut pit. When the pit was filled, an impoundment was build across the lower end of the pit and the slurry overflowed onto undisturbed ground on one side and into an area of spoil ridges on the other. The thickness of such a CSD, as well as its chemical and textural characteristics, can vary greatly across the deposit (fig. 5).

METHODS

Figure 5. Idealized cross section showing variations in thickness of a complex coal-slurry deposit (such as the Chinook coal-slurry deposit) that was emplaced above undisturbed ground, a final-cut pit, and a spoil deposit.

Feature Identification
For this investigation, the paper maps of Eggert (1979) and Weismiller and Mroczynski (1978) were digitized to provide a GIS layer showing the approximate locations of CSDs and associated preparation plants in the late 1970s. Locations of additional preparation plants that operated after 1978 were obtained from various reports published by the IGS (Hasenmueller, 1981, 1983, 1986, 1991; Alano and Shaffer, 1994; Blunck and Carpenter, 1997; Eaton and Gerteisen, 2000), as well as from various editions of the Keystone Coal Industry Manual (Coal Age, 1987, 1989, 1991, 1993, 1995, 2000, 2005).

Using the shapefile of approximate locations to identify areas of interest, about 160 historical aerial photographs taken in those areas between 1937 and 1980 were then obtained from the archives of the IGS and georeferenced. Other imagery that was used included Digital Orthophoto Quarter Quads (DOQQs) of the U.S. Geological Survey from 1998, and imagery of the National Agricultural Imagery Program from 2003 and the Indiana Orthophotography Project from 2005.

On aerial photographs, preparation plants are recognizable as tall structures that may cast long shadows and are sometimes associated with silos, conveyor belts, or smoke stacks (fig. 6). Preparation plants, particularly older plants and plants associated with underground mines, are often situated on rail lines (with multiple tracks adjacent to the plants), while more recent plants associated with surface mines are often connected to various pits by broad haul roads that are distinctive on aerial photographs. However, the plants (particularly those associated with surface mines) were often dismantled or moved soon after mining activity shifted to other areas.

Figure 6. Examples of preparation plants on aerial photographs. Left: Photograph of the Old Ben No. 2 preparation plant (ID_IGS: J1) and associated features taken in 2003 as part of the National Agricultural Imagery Program. The photograph has been rotated so that north is to the right. The width of the area shown is about 300 m. Right: Photograph of the Tecumseh preparation plant (ID_IGS: K2) taken in 1953 (Photo ID: QV-2M-39). The width of the area shown in the photograph is about 325 m.

As part of this investigation, the identification of coal-slurry deposits on imagery involved the evaluation of several factors. CSDs are typically situated close to preparation plants, although in some locations slurry is pumped or flows for considerable distances through pipes or ditches before entering a disposal cell. Other factors indicating the existence of a CSD include the presence of berms, a generally dark gray or black appearance (except where the deposit is highly oxidized or where salts have formed on the surface), the existence of braided or meandering stream channels (indicating a flat-lying deposit), and an absence of shadows (indicating that the deposit has low relief).

Older, unreclaimed CSDs may exhibit erosional features that typically have relatively low relief, in contrast to coarse-grained gob deposits, which were created by dumping refuse in large piles (fig. 7). Unreclaimed gob deposits are also typically dark gray to black in color, but they may also exhibit steep-sided, eroded edges that cast long shadows. Gob deposits may also show evidence of straight travel ways on their upper surfaces where dump trucks traversed the deposit.

Figure 7. The appearance of a coal-slurry deposit (left) and a gob deposit (right) at the Friar Tuck Mine (ID_IGS: D4) on September 30, 1974. The width of the area shown on the photograph on the left is about 550 m; the width on the right is about 400 m. Neither photograph has been enhanced. The bright white area on the south end of the gob deposit is where the gob had been burned (probably as a result of spontaneous ignition), resulting in the formation of baked shale ("red dog"). The arrows indicate the locations of photographs taken on the ground and shown in Figure 8.
Figure 8. View of the eroded surface of the Friar Tuck coal-slurry deposit (ID_IGS: D4) (left) and an eroded gob deposit (right) at the same mine site. See Figure 7 for the locations of the photographs.

Although both CSDs and gob deposits are typically dark gray to black, the more elevated (and drier) portions of CSDs are often light-colored to white because of more pronounced weathering or the formation of salts on the surface (figs. 9 and 10).

Figure 9. The most elevated and weathered portion of the Chinook coal-slurry deposit (ID_IGS: C1), as it appears on a black-and-white aerial photograph from 1976 (left) (Photo ID: 18021-173-76) and on a color photograph from 1996. The photograph on the left has been enhanced to increase brightness and contrast. The width of the area shown in each photograph is about 900 m.
Figure 10. During hot, dry periods in summer, white salts precipitated on portions of the surface of the Friar Tuck coal-slurry deposit (ID_IGS: D4), prior to its reclamation. A detail of the surface is shown on the right.

MAPPING

Wherever possible, preparation plants were identified on historical aerial photographs or other imagery and their locations were digitized directly from the imagery using ESRI ArcMap to create a point shapefile showing exact locations (COAL_PREPARATION_PLANTS_IN.SHP). Sixty-nine preparation plants were so identified and mapped from photographs taken between 1937 and 2005. Eleven additional plants could not be identified on any available imagery, but their approximate locations were inferred from features on imagery, together with consideration of other documentary evidence. Because the names of some mines and associated preparation facilities change through time, a unique identification number (ID_IGS) was assigned to each facility. The identification number of the historical aerial photograph or other imagery from which each feature was digitized is provided in a database field named "ID_HAP." More information regarding the shapefile is provided in its metadata (COAL_PREPARATION_PLANTS_IN.HTML). Supplementary information regarding each preparation plant is provided in a Microsoft Excel spreadsheet (COAL_PREPARATION_PLANT_DATA.XLS). Fields and coded values that are used in the spreadsheet are defined in COAL_PREPARATION_PLANT_DATA.HTML.

Using historical aerial photographs and other imagery, features having characteristics similar to coal-slurry deposits, as well as selected features that were in proximity to preparation plants or to known CSDs, were identified and their boundaries digitized directly from the imagery to create an ESRI ArcMap polygon shapefile (COAL_SLURRY_DEPOSITS_IN.SHP). A selected subset of data extracted from the database file associated with this shapefile (COAL_SLURRY_DEPOSITS_IN.DBF) is provided in a Microsoft Excel spreadsheet (COAL_SLURRY_DEPOSITS_IN.XLS). The identification number of the historical aerial photograph or other imagery from which each feature was digitized is provided in an attribute field named "PHOTO." A total of 375 polygonal features were so mapped. A unique identification number (ID_IGS_PLY) was assigned to each feature.

Because historical aerial photographs are typically black and white and may be of poor resolution, and because CSDs are sometimes difficult to differentiate from gob deposits or other disturbed or barren areas associated with active mining, the recognition of CSDs required subjective interpretations by the investigator. Therefore, a qualitative indicator of the investigator's confidence in his interpretation was assigned to each feature in COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS in an attribute field named "GRADE." An explanation of these indicators is provided in the metadata for the shapefile (COAL_SLURRY_DEPOSITS_IN.HTML).

Subsequently, 97 features (representing 952 acres) that were initially considered to be possible CSDs were reevaluated, and, upon further consideration, it was decided that they probably do not contain slurry. Although these features were retained in COAL_SLURRY_DEPOSITS_IN.SHP, they are categorized as "NS" (namely, "not slurry") in an attribute field named "TYPE." Also, 80 water-filled features (793 acres) are categorized as "IMP" (namely, "impoundments"). These features may (or may not) contain slurry, but because they are filled with water in all available imagery, any slurry, if present, cannot be recognized. The remaining 198 features are categorized in the attribute field named "TYPE" as either "FCP" (namely, emplaced in a final-cut pit or inclined haul road), "GND" (namely, emplaced on unexcavated ground behind a berm), or "SPL" (namely, emplaced within ungraded spoil deposits). In addition to the ESRI ArcMap shapefile (COAL_SLURRY_DEPOSITS_IN.SHP), a map showing the locations of possible CSDs and associated preparation plants throughout the study area is available as an Adobe Acrobat PDF file (COAL_SLURRY_DEPOSITS_IN_MAP.PDF). A portion of the map showing the distribution of CSDs in the vicinity of Dugger, Indiana, is shown in fig. 11.

Figure 11. Map showing the distribution of coal-slurry deposits in the vicinity of Dugger, Indiana. The type of deposit is indicated by color, as follows: red, final-cut pit (FCP); orange, unexcavated ground (GND); green, spoil deposit (SPL). Impoundments (IMP) are shown in blue; areas that are probably not slurry (NS) are shown in black.

The historical development of some CSDs was complex. Wherever possible, photographs taken on various dates ranging from 1937 to 2005 were used to identify and map different stages in a CSD's development. Boundaries of various features (for example, berms, final-cut pits, spoil deposits) that were visible at the times when the photographs were taken were then digitized directly from the photographs.

At the Chinook Mine, for example, slurry was initially disposed of in a final-cut pit (fig. 12, 1946), situated between intact overburden to the north and a spoil deposit to the south. When the pit became full, a berm was constructed and the slurry overflowed onto the adjacent undisturbed ground and into the troughs between spoil ridges (fig. 12, 1954). The CSD eventually overtopped the ridges and its upper surface formed a broad flat surface that dipped gently to the south and southwest (fig. 12, 1996). The deposit was subsequently capped with a synthetic soil, and vegetation has been established (fig. 12, 2003).

Figure 12. Photographs of the Chinook Mine (ID_IGS: C1) showing changes in a coal-slurry deposit through time. The photographs from 1946 (Photo ID: EA-1D-169) and 1954 (Photo ID: EA-4N-96) have been enhanced to increase brightness and contrast. The color photograph from 2003 (by which time the entire area had been reclaimed) is from the National Agricultural Imagery Program; the photograph from 1996 is from the Indiana Department of Natural Resources, Division of Reclamation. The width of the area shown in each photograph is about 1,350 m.

After mapping of the CSDs was completed, the areal extents of each feature were calculated using the "Field Calculator" function in ESRI ArcMap. In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, areal extents (in acres) of each feature are provided in the attribute field named "AREA_ACRES."

Using color aerial imagery (leaf off) from the 2005 Indiana Orthophotography Project, supplemented by color aerial imagery (leaf on) from the 2003 National Agricultural Imagery Program, a subjective characterization of the reclamation status of each CSD was also made. In COAL_SLURRY_DEPOSITS_IN.SHP, these broad characterizations are provided in the attribute field named "RECL" and include values such as "active," "unreclaimed," "reclaimed with a soil cap," and "reclaimed with vegetation."

Thickness Estimations

In order to provide volumetric estimates of the mapped CSDs, it was necessary to make assumptions regarding the thicknesses of the deposits. For the purposes of this preliminary reconnaissance investigation, the following simplifying assumptions were made:

  1. The thickness of a CSD categorized as "FCP" (namely, emplaced in a final-cut pit or inclined haul road) is assumed to be equal to the depth of the coal bed that was mined. Also, the cross-sectional area of such a CSD is assumed to be rectangular. This assumption does not take into account any slurry that was emplaced by overflow above the tops of final-cut pits. Also, for the purposes of this evaluation, inclined haul roads and haul roads transecting spoil ridges are also included in the category of "FCP" at some mine sites.
  2. The thickness of a CSD categorized as "GND" (namely, emplaced on unexcavated ground behind a berm) is assumed to be equal to the height of its associated berm. It is assumed that the CSD was emplaced on undisturbed ground (rather than an excavated pit). The cross-sectional area of such a CSD is assumed to be rectangular.
  3. A CSD categorized as "SPL" (namely, emplaced within ungraded spoil deposits) is assumed to completely fill the troughs between parallel ridges. Spoil ridges are assumed to have an angle of draw of 30 degrees on both sides, so that the troughs between them are assumed to have cross-sectional areas that are isosceles triangles. For the purposes of this project, the maximum thickness of a CSD within any given trough is assumed to be approximately equal to one-fourth of the average spacing between ridges, and the average thickness is assumed to be approximately equal to one-eighth of the average spacing. This assumption does not take into account any slurry that was emplaced above the tops of spoil ridges.


Site-specific drilling data from archival records of the IGS are available for 24 features. In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, the number of drill holes that were drilled in each of these features is provided in the field named "IGS_SAMPLE." For all other features that were mapped, it was necessary to estimate thicknesses of deposits using various other types of data, as follows:

  1. FCP. Depths to coal beds in the vicinity of CSDs emplaced in final-cut pits were obtained from two sources: (a) information on surface mines contained in the Coal Mine Information System (CMIS); and (b) drilling-log data that are tabulated in the National Coal Resource Data System (NCRDS). In general, the approximate elevation of the coal bed was determined from the drill hole that is geographically closest to the CSD feature. The depth of the coal bed at the feature was then calculated by subtracting the coal bed's approximate elevation from the elevation of ground at or near the feature. Where data are available from both the CMIS and the NCRDS, preference was given to the NCRDS data. For many features, a range of ground elevations exists, so that values for a "minimum" and "maximum" thickness are provided.
  2. GND. The heights of berms associated with CSDs emplaced on undisturbed ground were estimated from topographic contour data contained in digital line graphs (DLGs) derived from 1:24,000-scale quadrangle maps of the U.S. Geological Survey.
  3. SPL. The average spacing of spoil ridges associated with CSDs emplaced in troughs between such ridges was determined by measurements made directly from georeferenced historical aerial photographs and other imagery. Wherever possible, the measurements were made on the spoil ridges where slurry was later emplaced; where slurry was already present in all available imagery, measurements were made on nearby spoil deposits that were presumably associated with the same coal bed. As described above, the average thickness of the deposit was then assumed to be equal to one-eighth of the average spacing between ridges.


In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, estimated thicknesses (in feet) of slurry for each feature are provided in the attribute fields named "THK_MIN_FT" (lower thickness estimate) and "THK_MAX_FT" (upper thickness estimate). Of the deposits that are categorized as FCP, GND, and SPL, there are several situations for which thickness estimates are not possible in the absence of site-specific field data. These include:

  1. Graded spoil deposits. In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, these features are indicated by a value of "Y" ("yes") in an attribute field named "SPL_GRADED."
  2. Active areas where slurry emplacement (or removal) had recently occurred, as indicated by changes that are evident by comparison of aerial photography taken in 2003 and 2005. In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, these features are indicated by a value of "Y" ("yes") in an attribute field named "ACTIVE."
  3. Excavated pits, other than final-cut pits and impoundments on undisturbed ground. In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, these features are indicated by a value of "Y" ("yes") in an attribute field named "PIT_OTHER."


After thickness estimations were completed, the areal extents of each feature were multiplied by the estimated thicknesses using the "Field Calculator" function in ESRI ArcMap. In COAL_SLURRY_DEPOSITS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.XLS, volumetric estimates (in cubic yards) of slurry in each feature are provided in the attribute fields named "VOLMIN_YD3" (lower volumetric estimate) and "VOLMAX_YD3" (upper volumetric estimate).

Chemical Characterization

Although Miller and Eggert (1982) summarized the chemical analyses for coal-slurry samples collected by the IGS from the 1970s through the early 1980s, many of the individual records in that archive were never published. For the purposes of this project, these analytical results were compiled from unpublished paper records into a Microsoft Excel spreadsheet (COAL_SLURRY_ANALYSES_IGS.XLS). Excluding physical composite samples from drill holes where individual samples are available, the spreadsheet includes records for a total of 473 individual samples analyzed for sulfur (weight percent, as received), ash (weight percent, as received), and Btu per pound (as received, and moisture- and ash-free). The spreadsheet includes worksheets titled "individual samples," "site averages," "site and mine average," and "mine averages."

Historic maps show the locations of 93 different drill holes at 10 different mines, including the following mines: Airline, Buckskin, Chinook, Friar Tuck, Green Valley, Hawthorn, Lynnville, Minnehaha, New Hope, Otter Creek, Pandora, and Tecumseh. A total of about 450 samples were obtained from these drill holes. The maps are derived from published reports (Eggert and others, 1980, 1981), unpublished reports in the IGS archives (Harper and others, 1988, p. 35-37; Harper and others, 1989, p. 34-44), and unpublished paper maps associated with data records. These maps were used to compile an ESRI ArcMap point shapefile (COAL_SLURRY_SAMPLES_IGS_IN.SHP) showing the locations of the drill holes. Selected average analytical results for each drill hole are included in the shapefile. Compilation of the shapefile is described in its metadata (COAL_SLURRY_SAMPLES_IGS_IN.HTML).

Using historical aerial photographs, it is possible in some places to identify or infer the locations of points where slurry was being discharged from pipes or ditches into disposal cells (see fig. 3, "Entry Point"). Wherever possible, the locations of such points were digitized from imagery and are included in an ESRI ArcMap point shapefile (COAL_SLURRY_DISCHARGE_IN.SHP). More information regarding this shapefile is provided in its metadata (COAL_SLURRY_DISCHARGE_IN.HTML). A total of 74 possible discharge points were identified and mapped.

A population of 434 samples was evaluated to determine if statistically significant trends for calorific value, sulfur, and ash exist within individual CSDs. Several statistical analyses were performed to: (1) evaluate whether statistically significant vertical trends are represented by individual samples within drill holes, (2) test whether vertical trends in the drill holes have any predictable lateral variability relative to the locations of associated discharge points (if known), (3) determine if lateral trends exist in average values of selected chemical parameters, relative to the locations of associated discharge locations (if known), and (4) evaluate whether an analysis of spatial autocorrelation would provide a measure of the amount of clustering or dispersion present in the average values of the chemical parameters in the drill holes.

For the statistical analysis of vertical trends, statistical functions embedded within Microsoft Excel were used to apply linear least-squares regression to values for individual samples from 78 drill holes. Statistical significance at 95- and 99-percent confidence levels was determined for trends within each hole, based on the number of samples from each drill hole, which ranged from 2 to 12. Parameters that were statistically analyzed included calorific value (Btu per pound, dry), sulfur (weight percent, dry), and ash (weight percent, dry).

For the statistical analysis of lateral trends, the Statistical Analyst extension of ESRI ArcGIS was used to determine straight-line distances between drill holes and their associated discharge points (if available). Linear least-squares regression was then conducted to evaluate whether vertical trends of chemical parameters (represented by the value for the rate of change of a given parameter) in each drill hole exhibited a lateral trend relative to the locations of associated discharge points. Parameters that were statistically analyzed included calorific value (Btu per pound, dry), sulfur (weight percent, dry), and ash (weight percent, dry). A similar analysis was also conducted using linear least squares regression to identify any statistically significant lateral trends in the average chemical parameters for each drill hole, relative to the associated discharge point. For this analysis, parameters that were statistically analyzed included calorific value (Btu per pound, as received), sulfur (weight percent, as received), and ash (weight percent, as received). The statistical significance of the resultant trends was evaluated at the 95- and 99-percent confidence levels, based on the sample size (degrees of freedom).

The Statistical Analyst extension of ESRI ArcGIS was also used for the spatial autocorrelation analysis. The inverse distance option was used to calculate Moran's Index, which is a measure of spatial autocorrelation. The software itself provides an interpretation of the Moran Index, categorizing each analyzed data set as "random," "dispersed," or "clustered." Ten different CSDs were evaluated, and average values for drill holes that were statistically analyzed included calorific value (Btu per pound, as received, and moisture- and ash-free), sulfur (weight percent, as received), and ash (weight percent, as received). For all CSDs, the number of samples available for statistical analysis was smaller than the minimum number recommended for such analyses.

RESULTS

Areal Estimates
The total acreage of possible CSDs identified in this investigation was 2,765 acres. By category of emplacement, this includes the following:

  1. Emplaced in final-cut pits and inclined haul roads (FCP) - 764 acres (75 features);
  2. Emplaced on unexcavated ground behind a berm (GND) - 1,213 acres (74 features);
  3. Emplaced within ungraded spoil deposits (SPL) - 788 acres (49 features).


Based on inspection of color aerial photographs from 2003 and 2005, the reclamation status of each CSD was subjectively characterized. Of the total area of 2,765 acres, these characterizations are as follows:

  1. Active emplacement or reclamation - 223 acres (8 percent);
  2. Soil cap emplaced but not yet revegetated - 304 acres (11 percent);
  3. Revegetated - 1,277 acres (46 percent);
  4. Unreclaimed - 960 acres (35 percent).


Thickness Estimates

Among the features categorized as FCP, GND, and SPL, there were several subtypes of deposits for which thickness estimates were not possible in the absence of site-specific drilling data. Of the total mapped acreage of 2,765 acres, the total acreage of such subtypes was 409 acres. These subtypes included:

  1. Active areas where slurry emplacement (or removal) had recently occurred, as indicated by changes that are evident by comparison of aerial photography taken in 2003 and 2005 (223 acres, 15 features);
  2. Graded spoil deposits (162 acres, 11 features);
  3. Excavated pits, other than final-cut pits and impoundments on undisturbed ground (25 acres, 3 features).


Thickness estimates for features in the categories of FCP, GND, and SPL (including the 2,356 acres for which such estimates were possible) are summarized in Table 1. Because a range of estimates was determined for some features, the lower estimates are designated as "MIN," while the upper estimates are designated as "MAX" (units are "feet").



Table 1. Thickness estimates for coal-slurry deposits emplaced in final-cut pits (FCP), on unexcavated ground (GND), and within spoil deposits (SPL)
Minimum min Maximum max Average min Average max Median min Median max
FCP 0 125 38 56 30 50
GND 0 54 10 14 10 10
SPL 0 49 6 8 7 7


Volumetric Estimates

Using the thickness estimates, volumes of individual features were then calculated. Total volumes, by category of emplacement, are as follows:

  1. FCP (742 acres) - minimum = 56,563,329 yd3, maximum = 85,679,439 yd3;
  2. GND (991 acres) - minimum = 29,244,928 yd3, maximum = 38,527,746 yd3;
  3. SPL (623 acres) - minimum = 8,543,733 yd3, maximum = 12,151,611 yd3.


Thus, the total volumetric estimate for CSDs (FCP plus GND plus SPL) ranges from about 94 to 136 million cubic yards. These estimates do not include 409 acres of features for which thickness estimates are not possible, including deposits emplaced on graded spoil and in excavated pits, and in areas where slurry is being actively emplaced or removed.

Tonnage Estimates

The estimate of 94 to 136 million cubic yards, given above, is for the volume of raw slurry in situ. In order to convert this estimate to tons of potentially recoverable coal, several additional assumptions are required regarding (1) mineability of raw slurry, (2) weight density of raw slurry, and (3) recoverability of coal from raw slurry by processing. Data on which to base these assumptions are very limited.

With regard to mineability, slurry that was emplaced in ungraded spoil deposits presents the greatest problems for economic extraction because of the irregular profile of the underlying, steep-sided spoil ridges. It might not be possible to extract slurry from much more than 60 percent of such CSDs without encountering unacceptable contamination of the product with rock (Roger Missavage, Southern Illinois University, written commun., 2007). Similarly, extraction of slurry from final-cut pits would be limited within portions of the deposits that are bounded by spoil, so that perhaps only 70 percent of such CSDs are subject to economic extraction. Applying such broad assumptions to the CSDs included in this investigation, a more realistic estimate of mineable slurry may be 74 to 106 million cubic yards. If we assume that raw slurry in CSDs has an average weight density of about 110 to 120 pounds per cubic foot, then these volumetric estimates represent 110 to 171 million tons of potentially mineable raw slurry.

Based on the results of laboratory washability tests, Miller and Eggert (1982, p. 54-55) indicated that about 40 percent of CSDs may be recoverable coal. Recovery under actual field conditions would probably be somewhat less--perhaps as little as 20 percent (Roger Missavage, written commun., 2007). If we assume that 20 to 40 percent of mineable slurry may be recoverable coal, then the estimate of mineable slurry (namely, 110 to 171 million tons) represents 22 to 69 million tons of recoverable coal. This compares with an estimate made in 1982 that about 20 million tons of usable coal could be recovered from CSDs in Indiana (Miller and Eggert, 1982).

All the estimates given above regarding mineable slurry and recoverable coal are based on very limited field and laboratory data, and different assumptions may yield significantly different estimates of recoverable coal.

Chemical Characterization

Average values. Table 2 shows selected statistical values for the 473 individual samples that were chemically analyzed by the Indiana Geological Survey during the 1970s and 1980s and whose chemical values are included in the Microsoft Excel spreadsheet named "COAL_SLURRY_ANALYSES_IGS.XLS":



Table 2. Selected statistical values for 473 individual samples of coal slurry.
AR: as-received; MAF: moisture- and ash-free; wt %: weight percent
Ash, AR (wt %) Sulfur, AR (wt %) Btu/lb, AR Btu/lb, MAF
Minimum 5.6 0.4 1069 3725
Maximum 76.8 23.7 11720 24975
Average 32.2 4.0 7095 12849
Mode 26.7 2.8 7540 13210


Although determinations of moisture content were reported for some samples, those analyses are less reliable and are not included in the table above; the more reliable analyses indicate that moisture content was generally less than 30 percent (as received).

Of the 473 archival chemical records, locations are known for 450 samples, which were obtained from 93 drill holes at 10 different mine sites. Average values for each of the 10 mine sites are included in Table 3.



Table 3. Selected statistical values for samples from various mine sites.
AR: as-received; MAF: moisture- and ash-free; wt %: weight percent
Mine ID_IGS No. of
drill holes
No. of
samples
Ash AR
(wt %)
Sulfur AR
(wt %)
Btu/lb AR Btu/lb MAF
Minnehaha D3 18 74 20.2 2.2 6893 13680
Green Valley B4 9 23 20.9 5.1 9780 13305
Otter Creek B1 4 4 26.7 2.6 8893 13025
Friar Tuck D4 9 37 28.1 2.1 8092 13663
Buckskin K3 7 17 29.0 2.7 8589 12873
Chinook C1 14 81 30.5 3.2 5577 13310
Lynnville K1 6 36 35.0 4.3 8150 13344
Tecumseh K2 4 28 35.9 8.9 7168 11942
Airline E3 11 99 42.4 4.4 7143 12657
Hawthorn E4 11 55 45.2 5.8 6608 11920
SUM 93 454
AVERAGE 31.4 4.1 7689 12972


In general, average calorific values of CSDs are slightly higher at sites where average ash content is lower; however, the range of average calorific values (Btu per pound, moisture- and ash-free) is small, reflecting small variations in the rank of the coal processed by the preparation plants.

Although published reports (Eggert and others, 1980, 1981; Miller and Eggert, 1982) make reference to grain-size and washability analyses performed on samples collected by the IGS during the 1970s and early 1980s, only a relatively few records of those analyses have been discovered in the IGS archives.

Historical trends
The technology of coal preparation has improved greatly since the 1920s, so that one might expect higher overall ash contents and lower overall calorific values in deposits that were produced by more modern operations. Operational starting dates for the 10 mine sites in the table above range from 1921 to 1966 (see COAL_PREPARATION_PLANT_DATA.XLS). Graphs showing relationships between starting dates of preparation plants and average values of ash (weight percent, as received) and calorific value (Btu per pound, moisture- and ash-free) in associated CSDs indicate trends that are consistent with expected changes (fig. 13). However, simple statistical analysis of ash and calorific values versus starting dates reveal no statistically significant correlation at a 90-percent confidence level. Consequently, based on the limited number of samples in the IGS archive, we cannot make predictions regarding the overall quality of a CSD based on the age of the preparation plant from which it was derived.



Figure 13. Graphs showing relationships between starting dates of preparation plants and average values of ash (weight percent, as received) and calorific value (Btu per pound, moisture- and ash-free) in associated coal-slurry deposits.

Source coal beds
In Indiana, several different coal beds have been mined on a commercially significant scale. At the ten mine sites from which samples were obtained by the IGS, the coal beds that were processed include the Danville, Hymera, Springfield, Survant, and Seelyville Coal Members (see COAL_PREPARATION_PLANT_DATA.XLS) of the Dugger, Dugger, Petersburg, Linton, and Staunton Formations, respectively. In general, the Seelyville Coal is considered to be of relatively lower quality (namely, relatively high sulfur content), while the Survant and Danville Coals are considered to be of relatively higher quality (Mastalerz and Harper, 1998). At several of the sites, coal from two or more different coal beds were processed through the preparation plant, but no records are available regarding the relative contributions from each coal bed. With the very limited data available, there is no evident relationship between either the average calorific content (Btu/lb, moisture- and ash-free) or average sulfur content (weight percent, as received) of coal slurry at a mine site and the particular coal beds that were processed through the preparation plant.

Type of mining
In the past, coal produced by surface mines was considered to be of somewhat lower quality (namely, higher ash content) than coal produced by underground mines. At the ten mine sites from which coal-slurry samples were obtained by the IGS, seven were surface mines only, one was an underground mine only, and two received coal from both underground and surface operations. With regard to average calorific value of coal slurry, the three sites where coal was processed from underground mines rank among the highest five. With regard to average sulfur content (weight percent, as received), these three sites rank among the lowest four, so that there does appear to be a general relationship between type of mining (namely, surface versus underground) and overall quality of associated CSDs.

Spatial trends
Among the 78 drill holes that were evaluated statistically for vertical trends of calorific value, sulfur, and ash, samples from 47 drill holes at nine mine-sites exhibit statistically significant vertical trends at either 95- or 99-percent confidence levels for at least one parameter. For example, 32 drill holes show a significant trend in calorific value (Btu per pound, dry), of which 19 show an increase with depth and 13 show a decrease. Similarly, 29 drill holes show a statistically significant vertical trend in ash (weight percent, dry), of which 14 show an increase with depth and 15 show a decrease. Of these 29 holes, 25 are holes that also exhibit vertical trends in calorific value, and, in every instance, there is, as expected, an inverse relationship between the trends in calorific value and ash. Among the 78 drill holes, 31 did not reveal any statistically significant vertical trends.

Among the 25 holes in which vertical trends of both ash and calorific value are statistically significant, 5 are in settings characterized as final-cut pits, 12 are on undisturbed ground behind berms, and 8 are in ungraded spoil deposits. For example, four of the holes are located in the final-cut pit at the Airline Mine in a depositional setting that was presumably relatively simple, but eight of the drill holes are located in CSDs associated with the Chinook and Lynnville Mines, where the depositional history of slurry was relatively complex. Furthermore, among seven CSDs that contain two or more drill holes exhibiting statistically significant vertical trends, the trends within three of the CSDs are in reverse directions, so that ash increases downward in one or more holes but decreases downward in the other holes within the same deposit. These findings indicate that statistically significant trends are as likely to occur in complex depositional settings as in presumably simpler settings, and within any given CSD, vertical trends may be in reverse directions in different portions of the same deposit.

Ten CSDs were analyzed for statistically significant lateral trends in chemical data for vertical samples from individual drill holes. For each drill hole, the vertical rate of change of each chemical parameter (namely, the slope of the linear best-fit line) was used in this analysis. In only three CSDs, one or more chemical parameters are characterized as having a statistically significant trend at the 95-percent confidence interval, relative to the associated discharge point. Only one CSD at the Chinook Mine (ID_IGS_PLY = C1_3) showed statistically significant trends in all three chemical parameters tested: calorific value (Btu per pound, dry), ash (weight percent, dry), and sulfur (weight percent, dry). The spatial variability at the Chinook mine, both vertically and laterally, appears to be complex but of a potentially predictable nature.

Two measures of lateral trends were used to evaluate the average values of chemical parameters from various drill holes within individual CSDs: linear least squares regression and spatial autocorrelation. The parameters evaluated in this analysis were calorific value (Btu per pound, as received and moisture- and ash-free), sulfur (weight percent, as received), and ash (weight percent, as received). Ten CSDs were analyzed for statistically significant lateral trends using average values of chemical parameters. Lateral trends in at least one chemical parameter were present in CSDs at eight of the ten mines evaluated. The CSDs that showed the most consistent lateral trends across all parameters evaluated were at the Chinook Mine (ID_IGS_PLY = C1_3), Friar Tuck Mine (D4_1), and the Tecumseh Mine (K2_3). A CSD at the Hawthorn Mine (E4_2) showed statistically significant trends for three of the four parameters evaluated: calorific value (Btu per pound, as received), sulfur (weight percent, as received), and ash (weight percent, as received). In the statistically significant lateral trends, the calorific value increased with distance from the discharge point, whereas ash and sulfur content decreased with distance from the discharge point.

The spatial autocorrelation analysis showed that in five CSDs, one or more chemical parameters are characterized as "clustered," with a confidence level exceeding 95 percent. In two additional CSDs, at least one parameter is characterized as "clustered," but having a confidence level that is less than 90 percent. In the remaining three CSDs, lateral trends are characterized as either "dispersed," with a confidence level less than 90 percent, or "random." The CSDs having the strongest evidence of statistically significant lateral trends are at the Hawthorn Mine (ID_IGS_PLY = E4_2) and the Chinook Mine (C1_3).

The statistical analysis supports the findings of Eggert and others (1980, p. 259) regarding chemical trends at a CSD at the Airline Mine (IGS_ID_PLY = E3_1), where four drill holes within the final-cut pit had statistically significant vertical trends in calorific value (Btu per pound, dry) and ash (weight percent, dry), and where the lateral trend in sulfur content (weight percent, as received) was characterized as "clustered" with a confidence level of 99 percent. Similar evidence for potentially predictable trends also exists for the Hawthorn Mine, and, to a lesser extent, for the Chinook Mine. But statistical analysis of samples from other mines provides scant evidence of predictable trends. However, it must be remembered that the population of chemical values in the available data set is significantly smaller than the minimum number of values recommended for the types of statistical analyses that were performed.

SUMMARY

Preparation plants and associated coal-slurry deposits (CSDs) in Indiana were identified and mapped using georeferenced aerial photographs that were taken between 1937 and 2005. CSDs were categorized by three major depositional settings. The maps are available in the form of ESRI ArcMap shapefiles (COAL_PREPARATION_PLANTS_IN.SHP and COAL_SLURRY_DEPOSITS_IN.SHP). Supplementary information regarding preparation plants, such as dates of operation and coals that were processed, is available in a Microsoft Excel spreadsheet (COAL_PREPARATION_PLANT_DATA.XLS). The total area of CSDs in Indiana is estimated to be 2,765 acres.

Preexisting data sets were used to estimate the thickness of each CSD. The volume of each deposit was then calculated. Estimates of the total volume of coal slurry in Indiana range from 94 to 136 million cubic yards. An unknown quantity of additional coal-slurry exists at active coal-preparation facilities, in some water-filled impoundments located in the vicinities of inactive operations, in excavated pits of unknown depth, and in graded spoil deposits. Using certain assumptions regarding the ability to mine slurry from different types of CSDs, the weight density of raw slurry, and the ability to recover coal from raw slurry by processing, it is estimated that, as of 2005, the volume of mapped CSDs represents from 22 to 69 million tons of recoverable coal. This compares with an earlier estimate made by Miller and Eggert (1982) of about 20 million tons.

Textural and chemical properties of coal slurry are known to vary greatly within CSDs. In some depositional settings, it may be possible to predict variations based on knowledge of the point where the slurry was discharged from a pipe or ditch into its disposal cell (referred to as a "discharge point"). Inspection of aerial photographs was used to map such points. This map is available in the form of an ESRI ArcMap shapefile (COAL_SLURRY_DISCHARGE_IN.SHP).

The locations of 450 unpublished chemical analyses of samples that were collected by the Indiana Geological Survey in the 1970s through the middle 1980s were mapped, and the data were compiled into spreadsheets (COAL_SLURRY_ANALYSES_IGS.XLS). The map showing sample locations is available in the form of an ESRI ArcMap shapefile (COAL_SLURRY_SAMPLES_IGS_IN.SHP). Preliminary analysis of these data reveal no predictive relationships between the quality of coal slurry (as indicated by ash content and calorific values) and the age of the coal-preparation facility or the character of the coal beds that may have been processed through the facility. In general, however, facilities that processed coal from underground mines are associated with slurry of better quality than are facilities that processed coal from surface mines only.

Although the population of chemical analyses in the preexisting IGS archive was not originally intended for statistical evaluation and, in many cases, was smaller than the minimum number of values recommended for particular statistical analyses, the analyses were nevertheless performed to identify statistically significant spatial trends. The analyses included identification of vertical trends among samples from individual drill holes, as well as lateral trends among average values for drill holes within various CSDs. Among ten mine sites, vertical and lateral trends that are statistically significant at 95- and 99-percent confidence levels were identified for some CSDs. For example, the statistical analysis seems to support the observation by Eggert and others (1980, p. 259) that chemical and textural trends are "predictable and not random" at the Airline Mine. Statistically significant trends may also exist within CSDs that have relatively complex depositional histories, such as those at the Chinook and Lynnville Mines. However, no significant trends were identified among drill holes at several other sites.

RECOMMENDATIONS

The map that was produced by this investigation showing CSDs in Indiana is based on interpretations of aerial imagery and analysis of preexisting data. Further refinement and revision of the map, as well as volumetric estimates of individual CSDs, could be made in consultation with personnel of government agencies and mining companies who are familiar with conditions on the ground.

In the future, investigators involved in projects to characterize three-dimensional chemical and textural variations within CSDs should consider incorporating knowledge obtained from temporal series of historical aerial photographs to select sample sites.

Three-dimensional characterization of CSDs should include proximate (ash, sulfur, Btu) and ultimate (carbon, hydrogen, nitrogen, oxygen) analyses, as well as grain-size analyses, washability tests, petrographic analyses (involving coal macerals), chlorine and mercury contents, ash-fusion temperatures, and Gieseler plastometry. Collection of bulk samples (for example, samples weighing 500 pounds) should also be considered for selected bench analyses.

REFERENCES CITED

Alano, P., and Shaffer, K. R., 1994, Directory of coal producers in Indiana: Indiana Geological Survey Directory 12, 52 p.

Blunck, D. R., and Carpenter, J. A., 1997, Directory of coal mines and producers in Indiana-1997: Indiana Geological Survey Directory 12, 134 p.

Coal Age, 1926, September 26. Mine will extract coal under Wabash River and from adjacent land areas, p. 432-437.

_____, 1934, Private power plant cuts costs at Kings Station Mine from fourteen to six cents per ton: July, p. 267-268, 274.

_____, 1936a, Modernization program puts Sunlight stripping organization in tune with changing market demands: May, p. 189-192.

_____, 1936b, Indiana debates trade value of fine sizes; lubrication and safety discussed: July, p. 303-304.

_____, 1936c, Lump broken down and all sizes mechanically cleaned at Talleydale preparation plant: November.

_____, 1937a, Sealing, safety gains, power plants and cleaning highspot Indiana meeting: January, p. 37-39.

_____, 1938a, With modern preparation coals From Indiana fields are distributed over wide area: December, p. 41-42.

_____, 1938b, Coal preparation at Indiana mines: December, p. 96-104.

_____, 1948, Coal for a growing nation: January, p. 58-63.

_____, 1950a, Recovering sludge at Harco: September, p. 84-87.

_____, 1955a, Washery design cuts costs: June, p. 68-71.

_____, 1987, 1987 Census of North American preparation plants: January, p. 39-49.

_____, 1989, Plant census shows more than 400: November, p. 56-65.

_____, 1991, Prep plant census tallies less than 400: September, p. 41-48.

_____, 1993, 1993 prep plant census: September, p. 48-55.

_____, 1995, The 1995 prep plant survey adds more sites: October, p. 30-41.

_____, 2000, Prep plant population reflects industry: October, p. 31-38.

_____, 2005, Prep plant population rebounds: October, p. 20-31.

Eaton, N. K., and Gerteisen, S. P., 2000, Directory of coal mines and producers in Indiana-2000: Indiana Geological Survey Directory 12, 123 p.

Eggert, D. L., 1979, Map of southwestern Indiana showing locations of coal slurry ponds and preparation plants: Indiana Geological Survey Miscellaneous Map 28.

Eggert, D. L., Hailer, J. G., Irwin, P. N., and Miller, L. V., 1981, Energy content, composition, and associated water chemistry of wastes in the coal-preparation plant of the Green Valley-Wabash Mine, Vigo County, Indiana: Symposium on Surface Mining Hydrology, Sedimentology and Reclamation, December 7-11, 1981, University of Kentucky, Lexington, p. 143-149.

Eggert, D. L., Miller, L. V., and Irwin, P. N., 1980, Energy resources of the west tailings pond, Airline-Sponsler Mine, Greene County, Indiana: Symposium on Surface Mining Hydrology, Sedimentology and Reclamation, December 1-5, 1980, University of Kentucky, Lexington, p. 255-260.

Fiscor, S., and Lyles, J., 2004, Prep plant population reflects industry: 2003 Keystone Coal Industry Manual, p. 262-264.

Harper, D., Hartke, E. J., West, T., and Olyphant, G., 1988, Research and reclamation feasibility studies at the Friar Tuck site: First Annual Report to the Indiana Division of Reclamation from the Indiana Geological Survey, unpublished report, 161 p.

Harper, D., Hartke, E. J., Olyphant, G., and West, T., 1989, Research and reclamation feasibility studies at the Friar Tuck site, Part A--chemical analyses and hydrologic investigations: Second Annual Report to the Indiana Division of Reclamation from the Indiana Geological Survey, unpublished report, 145 p.

Hasenmueller, W. A., 1981, Directory of coal producers in Indiana: Indiana Geological Survey Directory 12, 74 p.

_____, 1983, Directory of coal producers in Indiana: Indiana Geological Survey Directory 12, 62 p.

_____, 1986, Directory of coal producers in Indiana: Indiana Geological Survey Directory 12, 60 p.

_____, 1991, Directory of coal producers in Indiana: Indiana Geological Survey Directory 12, 54 p.

Mastalerz, M., and Harper, D., 1998, Coal in Indiana--a geologic overview: Indiana Geological Survey Special Report 60, 45 p.

Miller, L. V., and Eggert, D. L., 1982, Composition and energy content of wastes from coal-preparation plants in Indiana: Eighth Kentucky Coal By-products Symposium, University of Kentucky, Lexington, p. 49-55.

Weismiller, R. A., and Mroczynski, R. P., 1978, Status of derelict land associated with coal mining in southwestern Indiana: Laboratory for Applications of Remote Sensing (LARS) Contract Report 022378, Purdue University.

Wobber, F. J., Wier, C. E., Leshenkok, T., and Beeman, W., 1974, Survey of coal refuse banks and slurry ponds for the Indiana state legislature using aerial and orbital inventory techniques: First Symposium on Mine and Preparation Plant Refuse Disposal, Coal and Environment Exposition, Louisville, Kentucky, p. 64-77.

_____, 1975, Coal refuse site inventories: Photogrammatric Engineering and Remote Sensing, v. 41, no. 9, p. 1,163-1,171.

BIBLIOGRAPHY

Coal Age, 1928, All equipment new and completely standardized at Indiana strip mine: August, p. 482-484.

_____, 1929a, World's largest strip mine has expectancy of 30 years: June, p. 335-337.

_____, 1929b, Strip pit air-cleans its fine coal: September, p. 526-527.

_____, 1931, Power generation part of modernization program of Indiana mine: September, p. 473-474.

_____, 1933a, Sherwood Mines again pioneer-this time in dehydrating and drilling: January, p. 7-8.

_____, 1933b, Maumee stripping swells list of operations using modern equipment and methods: September, p. 294-296.

_____, 1936d, Loading and cleaning both included in mechanization program at Templeton mines: January, p. 7-12.

_____, 1936e, New Bobolink stripping uses 30-yd. shovel and 25-ton trailers to mine 36-in. coal seam: April, p. 131-134.

_____, 1936f, Small stripping units produce high daily tonnage under Sternberg operating plan: August, p. 325-327.

_____, 1936g, Complete mechanization marks resumption of operations on Old Talleydale property: November, p. 491-497.

_____, 1937b, Chieftain 20 rescreener designed for effective 10-mesh dedusting when coal is damp: March, p. 117-119.

_____, 1937c, Small stripping units provide flexibility and high output under Siepman working plan: August, p. 355-357.

_____, 1938c, 12-yd. electric dragline strips 2 ½- to 3-ft. seam at Old Glory under 40 to 58 ½ ft. of cover: January, p. 67-70.

_____, 1938d, Electric trains cut cost of hauling coal from pit at Enos strip mine: April, p. 50-53.

_____, 1938e, Two seams stripped and prepared in all-welded plant at New Maumee Collieries operation: September, p. 29-34.

_____, 1939, 1,550-ton bin built in interval between two seams stores Fayette No. 4 Mine output: August, p. 44-49.

_____, 1940a, Mechanical cleaning plus air scrubbing and centrifuging feature the new all-welded Ayrdale plant: March, p. 40-43.

_____, 1940b, 34-in. coal seam recovered by 19-cu. yd. stripper with 5-yd. loader and 30-ton semi-trailers: August, p. 39-41.

_____, 1942, New shovel operation and 14-yd. dragline for rider work mark advances at Maumee mines in Indiana: March, p. 40-42.

_____, 1943, Rebuilt truck operation makes good: December, p. 81-83.

_____, 1944, High loader output reflects equipment and methods at Saxton: October, p. 95-105.

_____, 1946, 25-cu. yd. dragline heads modern units at new Maumee pit: February, p. 102-105.

_____, 1947a, Jones & Laughlin, National Steel plan large-scale developments: November, p. 129-130.

_____, 1947b, Coal on the locomotive front: December, p. 74-78.

_____, 1949, Maid Marian preparation: April, p. 96-102.

_____, 1950b, Efficiency and flexibility mark Jonay preparation: February, p. 86-91.

_____, 1951a, The Chieftain 20 story-1: January, p. 60-64.

_____, 1951b, The Chieftain 20 story-2: January, p. 65-69.

_____, 1952a, The Lumaghi story-1: May, p. 74-77.

_____, 1952b, Narrow-cut stripping and calcium-chloride washing: September, p. 80-85.

_____, 1953, Enoco builds for the future: May, p. 92-99.

_____, 1954, 42 Years in coal stripping: August, p. 60-63.

_____, 1955b, Stripping 30-In coal efficiently: February, p. 91-94.

_____, 1955c, Efficient deep mining, custom coal cleaning: April, p. 65-68.

_____, 1955d, A power-package for modern industry: June, p. 60-63.

_____, 1955e, Efficient three-product stripping: June, p. 73-75.

_____, 1956a, Blackfoot strips, hauls, cleans and dries two coals in an exercise in coordination: June, p. 60-65.

_____, 1956b, Modern cleaning, efficient stripping at Lynnville: July, p. 76-82.

_____, 1961a, Fluid-bed units dry 1x0 coal: May, p. 100-104.

_____, 1961b, Building coal quality: October, p. 188-195.

_____, 1964, The Blackfoot No. 5 story: July, p. 74-81.

_____, 1966, 75-yd dragline digs deeper to produce more: March, p. 78-81.

_____, 1968a, Old Ben rejuvenates Kings Station: January, p. 66-70.

_____, 1968b, Giant digs deep at Dugger: November, p. 54-60.

_____, 1969, Peabody's Miller plant serves two strip mines: January, p. 76-81.


For additional information regarding this project, you should contact Denver Harper (e-mail: dharper@indiana.edu) or Maria Mastalerz (e-mail: mmastale@indiana.edu) at the Indiana Geological Survey, 611 N. Walnut Grove, Bloomington, IN 47405



 
 
 
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