Mining accelerates the weathering of coal overburden. The weathering products of two minerals groups, iron sulfides and calcareous carbonates, dominate the chemical characteristics of postmining water. These minerals need only be present in an abundance of a few percent or less to be significant. By comparison the other 95% or so of overburden minerals play a minor role. The most important factor as to whether or not a site will produce alkaline drainage is the presence or absence of calcareous minerals. Pyrite, although necessary for acid formation, is of secondary importance, because if sufficient carbonates are present postmining water will be alkaline.

The coal-bearing rocks in Pennsylvania are from the Pennsylvanian and Permian? Periods of geologic time. The rocks of the Bituminous Coal Field of western Pennsylvania are divided, from oldest to youngest, into the Pottsville, Allegheny, Conemaugh, Monongahela, and Dunkard Groups. The majority of mineable coal occur in the Allegheny and Monongahela Groups. Several lithologic trends can be observed in this sequence of rocks. The clay/shale content increases upward from a low of about 25% in the Pottsville Group to highs of 70 to 80% in the Dunkard Group. In general there is a inverse relationship with sandstone, with sandstone increasing from ~20% or less in the higher Groups to a high of 50% in the Pottsville. The percentage of calcareous rocks increases upward. The Pottsville Group has less than 1% calcareous rock. The lower Allegheny is less calcareous (6%) than the upper Allegheny Group (14%). Rocks of the Casselman Formation in the Conemaugh Group and higher are greater than 50% calcareous. The percentage of sandstone that is calcareous generally reflects the percentage of overall rock that is calcareous. The uppermost Dunkard Group rocks contain the least amount of siderite, whereas over 20% of the strata in the Allegheny Group and Glenshaw Formation contain siderite. Within the Allegheny and Pottsville Groups sideritic rocks are more abundant than calcareous rocks.

The important depositional environments, from a mine drainage standpoint, are the location of marine zones and distribution of calcareous rocks. The marine rocks are frequently associated with high-sulfur strata, but can also have calcareous zones. Brackish rocks tend to have high sulfur and lack calcareous minerals. Marginally brackish (paralic) rocks frequently have less sulfur than their marine and brackish counterparts. Truly freshwater sediments tend to have calcareous minerals and limestone.

The strata in the Anthracite Region are divided, from oldest to youngest, into the Pottsville and Llewellyn Formations. The Pottsville Formation is entirely of a nonmarine depositional environment. As in western Pennsylvania, the dominant lithology of the Pottsville is sandstone and conglomerate, although the Pottsville of the Anthracite Region contains significant pebble conglomerates. The Pottsville contains up to 14 coal beds, but most are not mineable. The Llewellyn Formation consists predominantly of sandstone, but also contains conglomerates, plus lesser amounts of finer-grained rocks and coals. There are up to 40 mineable coals in the Llewellyn, the thickest and most persistent occur in the lower part of the formation. The Llewellyn and Pottsville Formations are believed to be nonmarine with the exception of the Mill Creek marine zone in the Northern Field. In addition to this marine zone, other calcareous rocks have also been found in the Northern Field. Some of the water quality reflects this source of alkalinity. Although stratigraphic studies have not yet identified calcareous rocks in the Southern and Western Middle Fields, highly alkaline mine waters imply that calcareous rocks exist. The lack of alkaline drainage in the Eastern Middle Field suggests a dearth of calcareous strata in this anthracite field.

Pleistocene glaciation came as far south as the northwestern corner of Pennsylvania’s bituminous coal field. Tills, where calcareous, can contribute significantly to the alkalinity of postmining water quality. Tills in the Northern Anthracite Field are not calcareous and do not contribute alkalinity to water.

Sulfur in sedimentary rocks occurs in three forms: sulfide (e.g., pyrite), sulfate, and organic. The oxidation of pyrite results in the formation of sulfuric acid and iron. This acid can dissolve other minerals, releasing other ions such as aluminum, manganese and magnesium. Sulfate minerals are typically weathering products of pyrite oxidation. Frequently these sulfate salts are essentially stored acidity and will produce acid when dissolved in water. Organic sulfur is generally assumed to produce little acid.

The most reactive carbonates in terms of their ability to neutralize acid are calcite and dolomite. The iron-carbonate, siderite, is a common mineral throughout the Pennsylvanian and Permian? strata of Pennsylvania, but it does not generate alkalinity. Calcite and dolomite not only neutralize acidity, but it appears that they can also contribute to the inhibition of acid production.

The presence or absence of calcareous minerals and pyrite is a function of several geologic processes. The paleodepositional environment and paleoclimate during the Pennsylvanian Period were important in determining the original mineralogic composition of strata. Paleoclimate influenced pyrite and carbonate concentrations for terrestrial rocks. For example, wet climates typically yielded less pyrite than dry climates and dry climates favored deposition of freshwater limestones. Rocks deposited in marine environments often have high sulfur and high neutralization potential. Brackish environments generally produce high sulfur with no calcareous minerals, although siderite can be present. High sulfur occurs in marine and brackish environments because of abundant sulfate ions in marine waters. This sulfate served as the source of pyritic sulfur. Marginally brackish environments are generally lower in sulfur and have little neutralization potential. Freshwater (terrestrial) deposits are often calcareous and frequently contain limestones. More recent geologic processes such as glaciation and surficial weathering have also influenced the mineralogy of coal overburden. Tills, if calcareous and of sufficient thickness, can contribute alkalinity to mine waters. Weathering by oxidation removes pyrite and by dissolution removes carbonates The relative depth of removal of these two mineral groups can be an important factor in determining the water quality potential of a mine site.

The geologic controls on coal overburden that have and are operating in Pennsylvania have resulted in overburden that can contain a wide range of concentrations of pyrite and calcareous minerals. Mine drainage quality reflects this variable mineralogy; water can be significantly alkaline to severely acidic.

Within Pennsylvania’s Bituminous Coal Field, mine drainage problems differ by stratigraphic horizon and geographic region. Acid problems are more significant in the lower Allegheny Group than in higher strata. Regional variations are often due to paleodepositional environment. For example, lower Allegheny overburden deposited in marine, brackish-marine, to marginally-brackish environments, will differ in the amount of pyrite and amount and type of carbonates present. The highest alkalinities are associated with the thick freshwater limestone sequences of the Pittsburgh Formation (Monongahela Group) in the southwestern corner of Pennsylvania, the thick marine Vanport limestone of the lower Allegheny Group in the central to northwestern area of the bituminous region, and the freshwater limestones of the upper Allegheny Group in areas where these limestones and associated calcareous shales are abundant. In addition, significant alkalinity concentrations occur in the Conemaugh Group where marine limestones are present, and the lower Allegheny Group mines in northwestern Pennsylvania where the overburden includes calcareous tills.

The highest acidity concentrations are associated with overburden: (a) of the Clarion and lower Kittanning coals, particularly where black brackish shales and thick marine shales predominate in the overburden, (b) in the Pittsburgh Coal and Waynesburg Coals of the southwestern portion of the bituminous region, in areas where the carbonate strata are absent or lack appreciable thickness, and (c) of Allegheny Group coals where sandstone predominates. The wide range of pH and the range in alkalinity and acidity concentrations for each stratigraphic group documents that some strata within each group has the potential to produce alkaline and acidic drainage.

Overall, mine water in the anthracite and bituminous regions has a bimodal distribution of pH. Water is either acidic or circumneutral. This is because Pennsylvanian Period rocks, at least in western Pennsylvania, can have significant concentrations of pyrite and calcareous carbonates. Calcareous overburden produces alkaline drainage and pyrite-rich and carbonate-poor overburden produces acidic drainage in the absence of appropriate pollution prevention techniques.

Regional-scale water quality variations are seen in the Anthracite Region. The most obvious being an absence of alkaline discharges in the Eastern Middle Field. The Eastern Middle Field also lacks severely acidic mine drainage. The Northern Field has proportionally more water with a pH above 5, than below 5. This is consistent with the finding of calcareous rocks in the Northern Field. The Western Middle and Southern Fields show a wide range of pH values. Combined data for all the anthracite fields display a bimodal distribution for pH similar to that for the Bituminous region.

An understanding of mine site geology is necessary for developing a representative drilling program, for providing information as to the acid or alkaline producing potential of strata, and for design of a groundwater monitoring program. Also, knowledge gained from these geologic factors can be used in developing site specific pollution prevention techniques such as material handling and calculation of alkaline addition rates. Geologic information is essential for determining the economic feasibility of a proposed mine site.

Geologic factors play a major role in the kind of water quality produced by a surface coal mine. This chapter examines those geologic factors with respect to the northern Appalachian Basin. Surface mining accelerates weathering by exposing fresh rock surfaces which contain minerals not at equilibrium with the newly mined environment. The two most important groups of minerals, in terms of postmining water quality impacts, are carbonates and sulfides. Weathering of the carbonates produces alkalinity and weathering of sulfides produces acidity. Other major ions can be calcium, sulfate, and iron. The weathering of other minerals also contributes to the composition of mine drainage, especially under low pH conditions. Some of these ions include manganese, magnesium and aluminum. The minerals available for weathering, and the resultant water quality, is to a large extent a function of geology. Some minerals were present at the time of deposition of the coal and enclosing sediments, while others are the result of more recent processes. More recent processes include near-surface weathering and effects from Pleistocene glaciation, such as deposition of till and glacial erosion.

Although acid mine drainage (AMD) is not unique to the northern Appalachians, the problem is more severe in this region than in any other coal producing region of the United States. Within Pennsylvania mine drainage problems differ by geographic region and stratigraphic horizon. Over the years some rules of thumb have been developed relating regional and stratigraphic geology to postmining water chemistry in Pennsylvania. An understanding of mine site geology is important in developing a representative drilling program, for providing information on the acid or alkaline producing potential of strata, and for design of a groundwater monitoring program. Also, knowledge gained from these geologic factors can be used in developing site-specific pollution prevention techniques, such as overburden handling and calculation of alkaline addition; in any case this geologic information is a necessary part of economic determinations.

All mine drainage prediction tools, and some of the prevention tools, in one way or another, require an understanding of the site’s geology. For example, many of the factors pertaining to the proper interpretation of previous mining as a prediction tool (Chapter 9) are related to an understanding of geologic similarities and differences between mine sites. Premining groundwater quality (Chapter 10) is dependent on the mineralogy of the rocks through which the water flows. Strategies to obtain representative samples for acid-base accounting (Chapters 6 and 11) and kinetic tests (Chapter 7) require an understanding of lateral and vertical facies changes of rock units and an understanding of the depth of weathering. Special handling (Chapter 14) requires a knowledge of the site stratigraphy and alkaline addition (Chapter 13) requires a knowledge of the relative amounts of pyrite and carbonates.

Figure 8.1 Generalized paleogeographic map of the Pennsylvanian depositional basin and source areas. Modified from Edmunds, et al. (1979).

Cyclicity in Pennsylvanian Period strata is a common phenomena in the United States (Cecil and Edgar, 1994). This cyclical pattern has been termed a "cyclothem" (Wanless, 1931). The "ideal" cyclothem is illustrated in Figure 8.3. The "ideal" cyclothem is a rare phenomena in Pennsylvania. Despite this, an overall cyclicity seems to be present. For example, in the Allegheny Group, the major coals are typically separated by ~50 ft (15 m) of sediments. The stratigraphic sequences associated with some of the Conemaugh marine invasions (e.g., Brush Creek and Ames) are most similar to the "ideal" cyclothem.

Figure 8.2 (Figure is in pocket at back of book). Generalized stratigraphic section of the bituminous coal field of western Pennsylvania showing stratigraphic nomenclature, positions of principal coals, marine zones, and major freshwater limestones. Also shown are distributions of rock types and carbonates that can influence mine drainage quality.

There appear to have been two major controls on regional cyclicity. One of these was basin subsidence due to collision between the North American and African plates. A second factor was climatic controls on sea level. Although, during the Pennsylvanian, the area of present day eastern North America was located near the equator and had a tropical climate, the southern polar regions of Pangea were experiencing widespread glaciation (Crowell, 1978; Veevers and Powell, 1987). Waxing and waning of continental glaciers resulted in episodic sea level changes, similar in amplitude to those during the Quaternary (~100 m; Heckle, 1995). Klein and Willard (1989) evaluated the relative impacts from these two mechanisms on the Pennsylvanian Period coal basins of the United States. They attribute the control of cyclothems in the Western Interior Basin to repeated transgressions and regressions of a mid-continent sea. These changes in sea level were caused by glaciation. Klein and Willard conclude, based on the more clastic nature of Appalachian sediments and the deeper basin warping, that the Appalachian Basin was affected most by tectonic controls. They also invoke a combination of transgressive-regressive cycles and tectonism as controls on cyclicity in the Illinois basin.

Two more factors have been proposed to explain the distribution of coals and intervening sediments. These are the "deltaic" model of Ferm (1970, 1974) and Donaldson (1969, 1974, and 1979) and the "climatic" model of Cecil et al. (1985) and Donaldson et al. (1985). The deltaic model accounts for rapid facies changes that occur over very short horizontal distances. These rapid changes are due to repetitive channel switching, as in the modern Mississippi delta. The climatic model explains the marked vertical stratigraphic, sedimentological, and mineralogic variations from the beginning to end of Pennsylvanian sedimentation, throughout the Appalachian Basin, and explains chemical and physical changes in coals through time. For example the red beds found in the Conemaugh Group are attributed to dry conditions. The widespread freshwater lake deposits of the upper Allegheny and Monongahela Groups are also indicative of dry conditions (Cecil et al., 1985). Skema and Lentz (1994) contend that deposition during the Pennsylvanian, within the region of present-day Pennsylvania, was complex. They conclude that multiple factors were at work. For example, Cecil et al.’s climatic model explains the widespread development of redbeds and freshwater limestones, and the glacial-eustatic model is consistent with widespread marine deposits in the lower Allegheny Group and Glenshaw Formation. The discontinuous nature of non-marine beds and abrupt facies changes imply more localized control, which Skema and Lentz (1994) attribute to "deposition on a fluvially prograding coastal plain" (p. 33). This process along with compactional subsidence explains much of the abrupt lateral stratigraphic changes observed in coal overburden. In summary, sedimentation in the northern Appalachians was complex and controlled by both basin-wide and local factors.

A generalized stratigraphic column of the Pennsylvanian and Permian(?) units of western Pennsylvania is depicted on Figure 8.2. Shown are the groups and formations, principal coals, marine zones, and major freshwater limestones. Additionally, lithologic information that is important to mine drainage quality is portrayed.

The lithologic descriptions of Figure 8.2 are based on an examination of 13 core logs in the files of the Pennsylvania Geologic Survey. Figure 8.4 shows the locations of the cores and Table 8.1 shows the formations that occurred within each core. The core logging was very detailed, with stratigraphic units as thin as 0.05 ft (1.5 cm) identified. For the purposes of this study, lithology was simplified to clay, shale, siltstone, sandstone, limestone, coal, and boney coal. Particular attention was paid to units that were calcareous and sideritic. Percentages of select lithology and calcareous and sideritic attributes are depicted by group or formation. In some instances, such as the Allegheny Group and Waynesburg Formation, these have been subdivided to provide more detail because of known differences in stratigraphy within the group/formation. The histograms should be viewed as semi-quantitative.

In addition to the core holes, overburden analysis drill holes with percent sulfur and neutralization potential (NP) were obtained from the permit files of the Department of Environmental Protection’s District Mining Offices. Percent sulfur furnishes an indirect estimate of pyrite content and neutralization potential furnishes an indirect estimate of calcareous carbonates (e.g., the minerals calcite and dolomite). NP in some instances may also reflect siderite. Pyrite and calcareous carbonates are the minerals that have the greatest influence on mine drainage quality. Examples are provided for all the major coals and some of the minor coals mined in Pennsylvania. The figures depicting stratigraphic logs show only total percent sulfur values greater than 0.25 percent, and neutralization potential (NP) values greater than 15 parts per thousand (ppt) CaCO₃. This has been done for clarity of the figures and because lower values typically have minimal influence on water quality. A key to these logs is shown in Figure 8.5.

Figure 8.5 Key to drill logs depicted in this chapter, showing lithologic symbols. Figures also show sulfur values greater than 0.25 percent sulfur (on left) and neutralization potentials above 15 ppt CaCO₃ (on right).

Glass et al. (1977) dedicated their report to George Hall Ashley (1866-1951) a former State Geologist of Pennsylvania and "life-long combatant with the perplexing rocks of southeastern Clearfield County." They point out that their work is built upon his foundation and that "(t)he geology was not as difficult as you thought, Dr. Ashley - it was worse!" The stratigraphy of the Pennsylvanian of Pennsylvania is not as simple as is often assumed. For most of the past 150 years stratigraphic correlations were made using the coal seams. The group-level boundaries are based on coal seams. The Allegheny Group, for example, was designed to contain all the mineable coals within that section of the Pennsylvanian, and the Pittsburgh coal defines the base of the Monongahela Group. Many coal seams are not continuous over large areas, some are only local. A good example is the Brookville coal, which marks the base of the Allegheny Group. This coal can only be precisely defined in the area where it was first described. Readers of this chapter will hopefully get some feel for the fact that the real world is not simple. Recent work by the Pennsylvania Geologic Survey has relied on laterally persistent units such as marine zones for correlation. This has proven to be much more reliable. As will be shown, many of these marine zones are quite extensive.

Whether to refer to the Pottsville and Allegheny as formations or groups is still in dispute and is not consistent in the literature. We have, for the most part, used the term "group." Resolution of which is the proper designation must be left to others. For a broader discussion of the Pennsylvanian stratigraphy, consult Edmunds et al. (1998). The quotes below from Edmunds et al. have had metric conversions added.

The Pottsville Group is variable in thickness. It is dominated by sandstone, and the coals are discontinuous. Because of the discontinuous nature of these coals, and the fact that they are often split with numerous partings, mining is not common in the Pottsville Group. The principal coal that is mined is the Mercer. This is actually a coal zone rather than a single coal. The Mercer clay, below the Mercer coal, has also been mined in some areas.

Edmunds et al. (1998) discuss the Pottsville of western Pennsylvania in terms of strata below the Mercer coal and above the Mercer coal.

V. Skema (Geologist, PA Geol. Survey, 1997, personal communication) has observed a complete absence of Pottsville rocks on areas of pre-Pottsville topographic highs in portions of Clinton County.

Edmunds, et al. (1998) state that

Figure 8.6 shows examples of Mercer coal overburden from Clarion and McKean Counties, PA. The Clarion County drill holes (DH 201-1, 201-2, and 201-3) are from the same mine site and all within a hundred or so acres (~40 ha). These holes illustrate the lateral and vertical variation of the Mercer coal zone. For example in hole DH 201-3 there are three coals, in DH 201-1 the zone is represented by six coals. The lateral correlation of any single coal can not be assured from drill hole to drill hole. The acid-base accounting data shows no significant calcareous strata (i.e., no NP > 30 ppt CaCO₃), but there are frequent high sulfur (sulfur > 0.5%) strata. As with the coals, the high sulfur rock units are not laterally continuous and they vary greatly in thickness. Discontinuous units, such as those shown in Figure 8.6 create problems for coal reserve studies because it is difficult to determine the lateral extent or thickness of a particular coal. Similarly, this geologic complexity makes overburden sampling very difficult.

A thorough understanding of mine site geology is necessary to insure that representative samples are selected. Complex stratigraphy can also make mine drainage prevention plans, such as special handling and alkaline addition, hard to design and implement.

Drill hole DH 177-9, from McKean County (Figure 8.6) contains one of the Mercer marine zones. This zone has a NP of 461 ppt CaCO₃. The two McKean County holes show more lateral continuity of the coals than did the Clarion County site. The marine zone, however, occurs in only the one hole. It is unknown whether the NPs from 30 to 40 ppt CaCO₃ equivalent are calcareous minerals or siderite.

Figure 8.2 shows the unconformable nature of the Pottsville Group. The Pottsville is dominated by sandstone, and is marked by a near absence of calcareous strata. Siderite occurs in about 13% of the strata. This lack of calcareous strata probably accounts for acid mine drainage problems that are often associated with mining of Pottsville coals and underclays.

Table 8.2 (Located in pocket at back of book). Postmining water quality of Pennsylvania Bituminous Coal Region by stratigraphic interval.

Typical examples of mine drainage quality of Pottsville Group coals and most other coal-bearing stratigraphic sections of the bituminous coal region of western Pennsylvania are shown in Table 8.2 (located in pocket at back of book). The water quality data contained in Table 8.2 were obtained from the surface mine permit files of the Department of Environmental Protection’s District Mining Offices. Whenever possible, the water quality data were obtained from the same permit files as the overburden analysis data shown on the drill logs in the figures contained in this chapter. This enables a direct comparison of the percent sulfur and NP data used to predict mine drainage quality, with the actual water quality monitored at the mine site. In some cases where during-mining and postmining water quality data were lacking for a site, the water quality data were obtained from nearby sites on the same coal seams. The relationships between the stratigraphic data described in this section and the mine drainage data contained in Table 8.2 and related tables are more fully described later in this chapter.

The Allegheny Group is one of two groups within the Pennsylvanian that contains the majority of economically mineable coals. For the purpose of discussion, the Allegheny has been divided into the upper and the lower Allegheny. The lower Allegheny extends from the base of the Brookville coal to the base of the Johnstown limestone (or upper Kittanning coal where the limestone is absent). The upper Allegheny extends from the base of the Johnstown limestone to the top of the upper Freeport coal. This division is made because "marine units occur only below the upper Kittanning underclay"… "and, with minor exceptions, nonmarine limestones occur only at or above that unit" (Edmunds, et al., 1998, p. 154). This distinction of "marine" and "nonmarine" is to a large extent based on the work of Williams (1960). Williams defined four faunal groups, inferred as "fresh-water", "restricted marine or near-shore marine", and two marine groups, one having a more diverse fauna than the other. Williams also relied on the geochemical investigations of Degens et al. (1957, 1958) in defining his depositional environments.

Williams (1960) interpreted the rocks in the Allegheny Group above the upper Kittanning coal (and including the Johnstown limestone below the coal) to be freshwater. This interpretation was based on fossil Esterids (now referred to as conchostracans or "clam shrimps"). Conchostracans are found above the upper Kittanning, lower Freeport, and upper Freeport coals (e.g., Williams, 1960; Edmunds, 1968). New analysis and interpretations of the ecology of conchostracans during the Pennsylvanian Period support a marginally-brackish environment. Thus, conchostracan-bearing sediments are not completely devoid of marine influence and therefore some marine sulfate would be available for reduction to sulfide sulfur (and pyrite). This is consistent with the sulfur content of the upper Kittanning and Freeport coals and roof rocks. The assignment of conchostracans as an indicator of freshwater depositional environments was debated at the time Williams wrote his paper, and is acknowledged by Williams. A detailed discussion of this topic is found at the end of this chapter in the Appendix.

Although conchostracan-bearing sediments apparently had some marine influence, it was less than that of brackish or truly marine sediments and this is often reflected in the lesser amount of sulfur and the thinner sequences of high-sulfur strata associated with conchostracan-bearing rocks. Marginal-brackish facies would be exposed to saline influences for less time during transgressive-regressive cycles than marine or brackish sequences; thus the thinner zone of high sulfur rock.

According to Edmunds et al. (1998) the Allegheny Group:

Because the Allegheny Group is extensively surface mined, and some portions of and areas within this formation have created acid mine drainage, the Department has an extensive database of acid-base accounting data for the Allegheny Group. For the purposes of simplifying discussion, the overburden above the upper Freeport, although part of the Glenshaw Formation of the Conemaugh Group, is included in the discussions as part of the upper Allegheny Group.

Lower Allegheny -The base of the lower Allegheny is defined as the base of the Brookville coal. This is not a useful working definition because the Brookville coal is not always present so that the base of the Allegheny may be difficult or impossible to define. What is often called the Brookville is probably often correlative with a lower Clarion coal. Thus, the base of the lowest Clarion coal often substitutes as a working definition. The Clarion and Brookville coals are not differentiated in this discussion.

Marine units occur over large areas and at several stratigraphic horizons within the lower Allegheny Group. The paleoenvironment of the marine zones can vary regionally and vertically. A good example of this is the Vanport horizon which occurs above the Clarion coal. The marine limestone facies covers an area of at least hundreds of square miles (km²) and is over 20 ft (6 m) thick in the center of the basin. A maximum thickness of over 40 ft (12 m) has been recorded for a small area in northeastern Lawrence County. Core logs in the files of the PaGS were examined to determine the extent of the Vanport zone south of the area mapped by Williams and Keith (1963). The presence of the Vanport marine horizon cannot be confirmed for the southwestern corner of the state because sandstone typically occupies this horizon. This sandstone may indicate non-deposition of limestone and the presence of distributary channels that emptied into the Vanport sea. Alternatively, but less likely, the sandstone may occupy channels that cut through and removed the limestone.

Clarion Coal Overburden and the Vanport Limestone - Where present, the Vanport can be a nearly pure limestone. Figure 8.7 shows the Vanport limestone in drill hole DH 23-6. Site locations for the drill logs with overburden chemistry are shown in Figure 8.4. The Vanport in DH 23-6 has a NP of 999 ppt CaCO₃. The Vanport in DH-4 in Figure 8.39 (presented in the section on glacial sediments) is greater than 920 ppt CaCO₃. The rocks below the Vanport are high sulfur (up to 4.1 % in DH 23-6 and up to 5.2% in DH-4). The high sulfur strata are 10 to 30 ft (3 to 10 m) thick. These high sulfur units are associated with NPs that are typically less than 35, but as high as 73 ppt CaCO₃. These low NPs may be due to siderite. These two logs represent, from the coal to the limestone, a transgressive sequence. The lower shale units have marginal marine (brackish) or shallow marine fossils and the limestone represents maximum transgression in Appendix for description of faunal facies). In drill hole DH 23-6 the high sulfur strata are associated with marine fossils. The strata for a drill hole in Black Lick Township, Indiana County (logged by Al Glover and Vic Skema, Pennsylvania Geological Survey) nicely show this transgressive sequence from brackish to marine conditions. Glover found Lingula and Dunbarella fossils immediately above the Clarion coal. These are indicative of brackish waters and represent the earliest portion of the marine transgression. Above this is a sandier zone that is bioturbated with siderite-filled burrows, typical of marine or brackish environments. Marine fossils and siderite concretions occur near the top of this unit. The next unit upward contains marine brachiopods, some of which are pyritized. This unit is overlain by the Vanport limestone which contains crinoids, an indicator of deeper, less muddy and consistently saline marine water.

Figure 8.7 Stratigraphy at Location 3, Porter Township, Clarion County. Interval is from the Clarion coal through middle Kittanning overburden. The overburden above all three coals is marine.

The Vanport horizon, which occurs above the Clarion coal, is often laterally (and vertically) transitional from marine to brackish conditions. Figure 8.8 and Figure 8.9 show regional changes in thickness of the Vanport limestone and the location of other contemporaneous facies in a portion of western Pennsylvania. In Butler County, where the Vanport is thick and in close proximity to the coal (Figure 8.9), mining of the Clarion coal will result in alkaline drainage. Where the Vanport-equivalent facies are brackish shale and the shale lacks calcareous minerals, such as in Clearfield County, the mine water is typically acidic. Figure 8.10 shows the distribution of pH for Clarion coal mine drainage from areas with and without the Vanport limestone. Median pH for areas without the limestone is 3.6 and with limestone is 5.0. Many of the mines were probably "pre-Act" and unreclaimed, and thus may be producing poorer quality water than would be produced by modern mining methods.

Figure 8.8 Generalized isopach map of the Vanport limestone and lateral facies for a portion of western Pennsylvania. Figure from Bergenback (1964).

Figure 8.9 Isopach map showing the thickness of rock between the Vanport limestone and the upper Clarion coal, and the rock-types/facies occurring directly below the limestone. The Vanport rests directly on the coal in northern Butler and southern Venango counties. Figure from Williams et al. (1964).

Lower Kittanning to Middle Kittanning Interval - Williams (1960) and Williams and Keith (1963) determined, using fossils, that the lower Kittanning (LK) was overlain by rocks deposited under marine, brackish (marginal marine) and freshwater depositional environments. The marine and brackish rocks are formally referred to as the Columbiana shale. They published maps showing the distribution of LK paleoenvironments. A revised map is presented in Figure 8.11. This map was derived from more recent published and unpublished studies by the Pennsylvania Geologic Survey (PaGS), and discussions with PaGS geologists (in particular, V. Skema and J. Shaulis), and BMR studies. The locations of LK drill holes discussed below are shown on this map. The faunal facies used to construct Figure 8.11 are discussed in the Appendix. The drill holes provide examples of sulfur and neutralization potential for coal and overburden deposited under different depositional environments.

Figure 8.10 Boxplots of pH of surface mine water from mines on the Clarion coal in areas where the Vanport limestone is present and in areas where it is absent. Lower boundary of the box represents the 25^th percentile, the upper boundary represents the 75^th percentile. The line between the two is the median. "Whiskers" indicate the range of data. Data are from Williams et al. (1982).

Figure 8.7 shows overburden of marine origin. Drill cores DH 23-6 and DH 18-1 contain marine brachiopods (e.g., Mesolobus) in the black carbonaceous shale overlying the lower Kittanning coal. The carbonate minerals siderite, dolomite and calcite were all identified within this zone at this site (Cravotta et al., 1994). High sulfur, identified as pyrite by Cravotta et al., is associated with the brachiopod-bearing rocks. The drill cuttings analyzed by Cravotta et al. did not encounter the highest NP zone located a few feet above the lower Kittanning coal. This zone with NP’s over 100 ppt CaCO₃ is probably calcite or dolomite. The alkaline postmining water quality confirms that calcareous minerals are present.

The lower Kittanning overburden is also marine in northeastern Armstrong County and southern Jefferson County (Figure 8.12). The drill logs show 30 or more feet (10+ m) of rock with over 0.5 % sulfur (2.37 % maximum). They also show NP’s in the range of 15 to 40 ppt CaCO₃. X-ray diffraction analyses indicate that calcite is the only carbonate present (R. Smith, PaGS, personal communication, 1996). The water associated with lower Kittanning mines in this area is alkaline despite the high sulfur overburden.

Figure 8.11 Tentative paleodepositional environment map for the rock above the lower Kittanning coal. Dashed line indicates uncertainty as to the actual location of the boundary between depositional environments; solid lines indicates that good paleontological control was available and boundary location is better known. Numbers identify locations of sites discussed in text and shown in figures. Fossil symbols are used to identify the area of a depositional environment and do not necessarily indicate that fossils occur at the location of the symbol. Sources used in the construction of this map: drill logs and site locations shown on Figure 8.4 and Table 8.1, Glass (1972), Edmunds (1968), Edmunds and Berg (1971), Berg and Glover (1976), Glover and Bragonier (1978), Williams and Keith (1960), personal observations by K. Brady, and insights gained from conversations with V. Skema, J. Shaulis and C. Dodge, all with the PaGS.

Figure 8.13 and Figure 8.14 show sulfur and NP for the lower Kittanning in Clearfield County where the overburden was deposited in a brackish depositional environment. Typically the shale above the coal is high in sulfur. Guber (1972) found that the high sulfur rocks often contain the brachiopod Lingula. Guber’s findings are discussed in more detail in a later part of this chapter. Lingula, as discussed in Williams (1960), is indicative of brackish environments. Geologic reports for the areas of the drill holes shown in Figure 8.13 and Figure 8.14 describe brackish fossils above the lower Kittanning coal (Glen Richey Quadrangle, Edmunds, 1968; Luthersburg Quadrangle, Edmunds and Burg, 1971; Ramey Quadrangle, Glass, et al., 1977). The high sulfur zones shown in Figure 8.13 near the middle of the shale above the LK coal in holes OB-1 (0.92 % S), OB-4 (4.4 % S) and near the top of the shale unit in A-8 (1.15 % S) contain Lingula. The NP that is present is probably due to siderite, the exception being the base of the sandstone and immediately adjacent shale in A-8, which is likely calcareous. LK mines in the brackish areas of Clearfield County are notorious for producing acid mine drainage.

Williams (1960) shows a small portion of the LK roof rock in northeastern Cambria County as having been deposited in what he defined as a freshwater depositional environment, based on the presence of conchostracans. Recent investigations by J. Shaulis and V. Skema (personal communication, 1997) have confirmed the presence of conchostracans in extreme northern Somerset County. Fossil fauna however are rare (Figure 8.11). LK overburden chemistry in this region does appear to be different from the other areas discussed above (Figure 8.15). Sulfur is seldom above 0.5 percent. The small amount of NP (between 15 and 36) may be siderite because the postmining water is not alkaline. Mines from these areas tend to produce mild acid mine drainage, with pH ~4 and acidity ~100 mg/L.

Middle Kittanning to Johnstown Limestone Interval - The middle Kittanning (MK) coal is overlain by marine or brackish sediments over most of Pennsylvania’s bituminous coal field. The exception is an area around Cambria County where the MK overburden has conchostracans or no fossil fauna. The marine zone is formally referred to as the Washingtonville Shale. Figure 8.16 is a map of paleodepositional environments for the rocks overlying the middle Kittanning coal. The northern portion of this map is from Williams (1960) and the southern portion is derived from drill

hole data made available by the PaGS and PaGS publications. This MK horizon, in a PaGS drill hole in northwestern Washington County, is represented by a coquina limestone. This was probably the deepest part of the MK "basin" in what is now Pennsylvania. Faunal facies used to construct this map are discussed in the Appendix.

The "MK" is a coal zone in many areas rather than a distinct coal seam. Over much of Clearfield County there are typically two to four "splits" of the MK. For example, in the Hazen, Reynoldsville, Falls Creek, and DuBois quadrangles the MK consists of a "middle Kittanning" that is typically two feet (0.7 m) thick and up to 42 inches thick (1.1 m) (Glover and Bragonier, 1978). This is the MK coal that is mined locally. This however is not the coal that the marine zone overlies. The marine zone overlies a "middle Kittanning rider" coal and the marine zone is about 30 ft (10 m) above

Figure 8.15 Drill logs depicting lower Kittanning overburden in the area of Cambria County that Williams and Keith (1963) indicated finding conchostracans. Holes 61-C and 61-B are in Reade Township, Cambria County (Site 9) and holes OB-1 and OB-2 are in Dean Township, Clearfield County (Site 10).

the "middle Kittanning" that is mined. This raises the likely prospect that the "middle Kittanning" seam being mined in one area may be a different split than that being mined in another area.

Holes showing the results of NP and percent sulfur above the MK coal (Figure 8.7, and Figure 8.14) were drilled in areas that are marine or brackish environments (Figure 8.16). The MK at Area 5, in the area of marine deposition, occurs beneath shallow cover which is probably weathered and therefore not very revealing for determining depositional controls on overburden mineralogy. Locations 7 and 8 (Figure 8.14; and see Figure 8.4 map for site locations) occur in the area of brackish overburden. The three holes with significant overburden (Hole 3, 68B02, and 560A3) have 30 to 40 ft (10 to 12 m) of high sulfur overburden overlying the

Figure 8.16 Tentative paleodepositional environment map for the rock above the middle Kittanning coal. Good paleontological control was available for construction of this map. Fossil symbols are used to identify the area of a depositional environment and do not necessarily indicate that fossils occur at the location of the symbol. The northernmost line showing the division between brackish and marine environments is essentially that of Williams and Keith (1963). Work for this chapter agreed with the location of this boundary. Other sources used for the construction of this map were: drill logs and site locations shown on Figure 8.4 and Table 8.1, Glass (1972), Edmunds (1968), Edmunds and Berg (1971), Berg and Glover (1976), Glover and Bragonier (1978), Williams and Keith (1960), personal observations by Keith Brady, and insights gained from conversations with V. Skema, J. Shaulis and C. Dodge, all with the PaGS.

coal. X-ray diffraction analyses reveal that the car-bonate present over the MK at Location 7 is siderite. It is uncertain whether the zone with a NP of 131 is siderite or a calcareous carbonate. X-ray diffraction showed strata from other holes with NP as high as 75 contained siderite and no detectable calcite. The high sulfur and abundance of siderite for brackish overburden is similar to that observed above the LK. The zone with an NP of 151 in the sandstone of drill log 560A3 is probably calcareous.

Figure 8.15 shows the MK in the area of the Figure 8.16 map where the MK is overlain by conchostracan-bearing shales. The highest sulfur in the overburden in drill log OB-1 is only 0.66 percent. This low sulfur is consistent with sulfur values from the conchostracan-bearing depositional environment for the LK coal. Further work needs to be done to establish relationships between concentrations of sulfur and carbonate minerals and depositional environment.

Upper Allegheny - The base of the upper Allegheny, as defined for this chapter, is the bottom of the Johnstown limestone. It is realized that this "limestone" is often transitional with the sediments below and does not occur everywhere, although it is remarkably persistent over much of the Bituminous Region and can be a good stratigraphic marker bed. Where the Johnstown limestone does not occur the base of the upper Kittanning coal substitutes as the base of the upper Allegheny. The reason for this stratigraphic break in the Allegheny is that this sequence includes nearly all the freshwater limestone units in the Allegheny Group. Fauna in the freshwater limestones is generally dominated by ostracods, spirorbis, and fish remains. This fauna is completely different from the fossils found in upper Allegheny coal-roof rock. Typically the only fossil fauna found in the rock above the coals in the upper Allegheny are conchostracans. The separate depositional environments of the roof-rock and the freshwater limestones is evidenced not only by the different faunas, but also by position and composition. The freshwater limestones are usually found below the coals, whereas the conchostracan-bearing rocks are above the coals. The "limestones" are highly calcareous and lack carbonaceous material, whereas the roof-rocks may not be calcareous at all and are often black due to abundant carbonaceous matter. It would appear that during the time of deposition of the upper Allegheny, coal deposition was followed by a marginally brackish transgression. Eventually truly freshwater sediments were deposited, including the freshwater limestones.

The Johnstown limestone is shown in Figure 8.17 and Figure 8.18. The Johnstown limestone has NP greater than 900 ppt CaCO₃ in LH-3 and 700 or greater in the other two drill holes in Figure 8.18. The high NP values are in the range of those of the marine Vanport limestone for "purity." Sometimes the Johnstown horizon is not a true limestone, but a calcareous claystone or shale (e.g., the zone just below the upper Kittanning coal in OB-9, Figure 8.17). Hole #101 in Figure 8.19 does not show a calcareous zone below the UK. This may simply be because the Johnstown limestone occurs below the bottom of this drill hole. The drill logs in Figure 8.20 are from an area where the Johnstown limestone does not occur. The limestone does occur, however, about a mile (1.6 km) west of these drill holes.

The interval between the UK coal and the lower Freeport (LF) coal often includes a calcareous zone beneath the LF coal. Where this zone is a limestone, it is referred to as the lower Freeport limestone. The interval between the LF and upper Freeport (UF) is similar to that of the underlying UK-LF interval. A widespread limestone or calcareous shale/claystone unit also lies beneath the UF coal. The rocks between the UK and LF, and LF and UF, as well as the overburden above the UF are portrayed in Figure 8.17, Figure 8.18, Figure 8.19, Figure 8.20, and Figure 8.21. The fauna of the Johnstown limestone, and LF and UF limestones are interpreted as freshwater in origin.

The lateral distribution of individual freshwater limestones in the Allegheny Group can be quite extensive, covering hundreds of square miles. The limestone is variable in thickness, and frequently there are areas where the limestone is absent. One freshwater limestone, the upper Freeport limestone, has been studied by Williams et al. (1968) and Weedman (1988). This limestone occurs between the lower and upper Freeport coals. Their findings illustrate the variability in thickness and distribution of an upper Allegheny limestone. Williams et al. (1968) looked at an area of approximately three 7.5 minute quadrangles in Clearfield County, and Weedman (1988) studied an area which covered slightly more than four 7.5 minute quadrangles in Indiana county. Observations by the authors confirm that this limestone is present, and persistent, between their two study areas. In Clearfield County, the thickness ranged from absent (where replaced by channel sandstone) to greater than 4 ft (1.2 m). Figure 8.22 shows the area studied by Weedman. The isopach map shows the variability in thickness that is typical of the upper Freeport limestone. Williams et al. (1968) indicate that the limestone in rare instances approached 100% calcium carbonate. Our experience is that these limestones are often "dirty" with a high component of clay and silt. At places this stratigraphic interval is represented by calcareous rocks with less than 50%

Figure 8.17 Overburden and chemistry of the interval from the Johnstown limestone to the Brush Creek marine zone. The overburden exhibits the calcareous nature of the upper Allegheny Group. High sulfur is typically restricted to the coal and immediately adjacent rock. This hole was drilled at Site 15 in Jackson Township, Cambria County.

calcium carbonate, and therefore by definition not a limestone, although they are often referred to as limestones on drillers’ logs.

In addition to freshwater limestones, the upper Allegheny Group frequently contains an abundance of calcareous claystones, mudstones and siltstones. Figure 8.20 shows a stratigraphic section in Fayette County, between the upper Kittanning and lower Freeport coals. Much of this interval is calcareous (NP > 100; i.e., >10% CaCO₃), but only small portions could be classified as limestone (> 50% CaCO₃).

The Conemaugh Group "is stratigraphically defined as the rocks lying between the upper Freeport coal horizon and the Pittsburgh coal. The thickness of this interval ranges from 520 feet (158 m) in western Washington County to 890 feet (270 m) in southern Somerset County. A gradual eastward thickening of the Conemaugh is apparent" (Edmunds et al., 1998, p. 154). The Conemaugh is subdivided into a lower formation called the Glenshaw, and an upper formation called the Casselman. The division is made at the top of the Ames marine limestone. Mineable coals are uncommon in the Conemaugh.

Figure 8.18 Upper Kittanning and lower Freeport overburden and chemistry for three drill logs at Site 15 in Jackson Township, Cambria County. The overburden exhibits the calcareous nature of the upper Allegheny Group. High sulfur is typically restricted to the coal and immediately adjacent rock.

Figure 8.19 Upper Allegheny Group overburden and chemistry at Site 12 in West Carroll Township, Cambria County. Note the thick freshwater limestone with NP’s over 500 ppt CaCO₃ above the lower Freeport coal.

Glenshaw Formation - The Glenshaw contains several widespread marine zones (see Figure 8.2). There are possibly as many as seven marine zones within the Glenshaw (Skema, personal communication, 1997). The Glenshaw is thickest in Somerset and southern Cambria counties, where it reaches 400 to 420 ft (122 to 128 m). It is thinnest near the Ohio border where it is about 280 ft (85 m) thick (Edmunds et al., 1998).

The Brush Creek limestone facies is present within most of its outcrop belt in western Pennsylvania. An area of more clastic shale and siltstone occupies the limestone horizon in Washington, southern Allegheny, northern Westmoreland, southern Indiana, and Cambria Counties (Skema et al., 1991). The Brush Creek coal, which occurs below the marine zone, is typically thin and not mined over much of western Pennsylvania. The coal is sometimes mineable in portions of the south-central and southeastern sections of the bituminous coal fields of Pennsylvania. Figure 8.23 shows Brush Creek overburden from Wharton Township, Fayette County and Figure 8.24 and Figure 8.17 show overburden from Jackson Township, Cambria County. The rock above the coal, in each area, has relatively high sulfur (> 0.5%) and relatively high NP (> 30 ppt CaCO₃). A true limestone is not present in any of these holes, the highest NP being 345 ppt CaCO₃ in OB-9 from Cambria County. Because the limestone or a calcareous facies is typically present where the Brush Creek coal is of mineable thickness, the drainage is generally alkaline.

Figure 8.25 shows overburden for the lower and upper Bakerstown coals. The Woods Run marine zone overlies the lower Bakerstown coal, although in Somerset County it is poorly developed and is represented by a brackish facies containing Lingula and Dunbarella (J. Shaulis, personal communication, 1997). Just below the upper Bakerstown coal a freshwater limestone sometimes occurs. This is evident in DH-12. The upper Bakerstown coal is commonly overlain by a black shale with abundant conchostracans in Somerset County (Shaulis, personal communication, 1997). This zone is the stratigraphic equivalent of the Noble marine zone, which is a restricted marine to brackish shale in some other portions of the bituminous field (Edmunds, et al., 1998).

The overburden above the lower Bakerstown coal is similar to lower Allegheny coal overburden with a brackish depositional environment. It is characterized by sulfur greater than 0.5 percent and NP generally 30 ppt CaCO₃ or less. The zones with higher NP, above the brackish zone, may be freshwater calcareous zones related to the freshwater limestone. Unfortunately it is hard to evaluate the overburden above the upper Bakerstown. The upper Bakerstown coal in Hole 11 F is only about 10 ft (3 m) below the surface. Holes DH-3 and DH-12 have sandstone and shale, respectively, above the coal. Both show some zones with elevated sulfur, but the sulfur in these drill holes is always less than 1.0 percent. NP is negligible. More comparisons need to be made, but this overburden looks similar to the lower Kittanning overburden in eastern Cambria County where conchostracans occur.

Figure 8.21 Lower and upper Freeport overburden and chemistry. Drill logs #17 and #18 are from Site 13 in Mt. Pleasant Township, Westmoreland County, and drill logs OB-15 and OB-14 are from site 14 in Clay Township, Butler County.

Figure 8.23 Brush Creek coal and overburden at Site 11 in Wharton Township, Fayette County. The overburden is of marine origin.

Casselman Formation - "The thickness of the Casselman Formation ranges from 230 feet (70 m) in the extreme western part of the Appalachian Plateaus province to 485 feet (148 m) in southern Somerset County" (Edmunds, et al., 1998, p. 156). With the exception of the marine shales above the Ames limestone, and the Skelly horizon, which occurs about 30 to 60 ft (9 to 18 m) above the Ames marine zone, the Casselman is made up of exclusively fresh water rocks. Redbeds, which are regionally discontinuous, are scattered throughout the Casselman in the western portion of Pennsylvania. "Eastward they become thinner and fewer in number. This trend continues into eastern Somerset and Cambria Counties, where large areas of the Casselman Formation are completely devoid of red beds. Conversely, coals are nearly absent or very thin in the west but increase in quantity eastward. In Somerset County, a few coals are thick enough to mine" (Edmunds, et al., 1998, p. 156).

Very little coal is mined in the Casselman Formation. Figure 8.25 shows overburden for the Wellersburg coal which is of mineable thickness only in the Wellersburg syncline of Somerset County (equivalent to the Georges Creek Field in Maryland). Although the overburden contains some strata with sulfur greater than 0.5 percent, the overburden is largely calcareous. Figure 8.26 displays chemical data for overburden above and below the Morantown coal, the uppermost coal in the Casselman. This coal is only mined in Somerset County. Shaulis (1993) feels the Morantown is actually a lower split of the Pittsburgh coal, which would place the coal in the Monongahela Group. One of the reasons cited for this stratigraphic placement is the presence of the freshwater limestone below the Morantown. This limestone occurs in OB-A in Figure 8.26 with an NP of 524. Whatever the stratigraphic position, the overburden in the two examples from Somerset County exhibits low sulfur and some neutralization capability. The Morantown, when it is present, is mined in conjunction with the Pittsburgh coal.

Monongahela Group

The Monongahela Group is

This sandstone channel is shown in Figure 8.27. The mineable coals in the Monongahela Group are restricted to the lower portion of the group. The number of mine sites with overburden data for the Monongahela Group in the files of the Department of Environmental Protection are few in number. This is not because the Monongahela coals are rarely mined, it is because mining almost always produces alkaline drainage, and water quality from previous mining is used as the prediction tool.

Pittsburgh Formation - The lower half of the Pittsburgh Formation contains the majority of mineable coals in the Monongahela Group. The Pittsburgh coal,

Figure 8.26 Overburden and chemistry of coal and rocks from the Morantown to the Redstone coals at Site 16 in Somerset County. This interval is considered to have been deposited entirely in a freshwater environment. Relationship to paleogeography at time of deposition of Pittsburgh overburden is shown on Figure 8.28.

which defines the base of the formation and group is unusually continuous, covering thousands of square miles (km²) and is unusually thick (5 to 10 ft; 1.5 to 3 m) for a coal of western Pennsylvania. The other major coals are the Redstone and Sewickley. In Somerset County an additional coal, the Blue Lick, occurs between the Pittsburgh and Redstone coals. Shaulis (1993) believes the Blue Lick coal is a split of the Pittsburgh coal.

Pittsburgh Coal to Redstone Coal Interval - Pittsburgh coal overburden varies from sandstone to limestone to shale. Figure 8.28 is a reconstruction of paleodepositional environments during the time of deposition of the Pittsburgh coal overburden.

Figure 8.27 Location, geometry and isopach map of a sandstone channel above the Pittsburgh coal in Green and Washington Counties. Isopach map modified from Donaldson (1979).

Sandstone was deposited in the distributary channel running through the southwestern corner of Pennsylvania. An isopach map of the thickness of this channel is shown in Figure 8.27. Limestone or shale was deposited in the lakes and on the mud flats. Some examples of the distribution of Pittsburgh Formation limestones in Greene County, PA and northern West Virginia, are illustrated by Figure 8.29, Figure 8.30, and Figure 8.33. Figure 8.29 is an isopach map of the Redstone limestone. Figure 8.30 is a cross-section of the Pittsburgh/Redstone interval. This cross-section is oriented east-west and approximately parallels the Pennsylvania-West Virginia border shown on Figure 8.29. The Redstone limestone is "patchy", which may simply be due to variable carbonate content of the lake-deposited sediments. The intervening shales may be a lateral, less calcareous, facies of the freshwater limestone. The drill logs shown in Figure 8.31 are from an area east of the major channel shown in Figure 8.27 (isopach map of Pittsburgh sandstone), but they show the nature of the Pittsburgh overburden when it is sandstone. It is characterized by some high sulfur strata, especially the shale portions of OB-2, and some calcareous zones within the sandstone (e.g., the zone in