Selenium Concentrations in Middle Pennsylvanian 

Coal-Bearing Strata in the Central Appalachian Basin 

By Sandra G. Neuzil, Frank T. Dulong, C. Blaine Cecil, Nick Fedorko, John J. Renton, and D. K. Bhumbla 

Open-File Report 2007–1090 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

Revised and reprinted: 2007 

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Suggested citation: 

Neuzil, S.G., Dulong, F.T., Cecil, C.B., Fedorko, N., Renton, J.J., and Bhumbla, D.K., 2007, Selenium 

concentrations in Middle Pennsylvanian coal-bearing strata in the central Appalachian basin: U.S. 

Geological Survey Open-File Report 2007-1090. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 

ii
Contents 

Executive Summary....................................................................................................................................................... 1 

Introduction .................................................................................................................................................................... 3 

Acknowledgments......................................................................................................................................................... 4 

Methods and Analyses................................................................................................................................................. 4 

Coring........................................................................................................................................................................... 4 

Core Sampling ............................................................................................................................................................ 5 

Selenium Analyses of Core Samples ..................................................................................................................... 6 

Analyses of Core Samples for Mineralogy and Major Element Oxides............................................................ 6 

Analyses of Total Sulfur and Loss on Ignition in Coal-Bed Roof, Parting, and Floor Samples.................... 7 

Leach Tests: Saturated Paste Extract (SPE) and Sequential Water Extraction (SWE) ............................... 7 

Results ............................................................................................................................................................................. 8 

Estimates of Analytical Precision ........................................................................................................................... 8 

Core Comparisons: A Test for Spatial Variation in Selenium Concentrations in Middle Pennsylvanian 

Coal-Bearing Strata................................................................................................................................................... 9 

Stratigraphic Variation.......................................................................................................................................... 9 

Regional Variation................................................................................................................................................ 10 

Frequency Distribution of Selenium Concentrations in Three Cores............................................................. 10 

Selenium Concentrations and Dominant Lithologies (Rock Types)................................................................ 10 

Selenium Concentrations in Roof, Parting, and Floor Samples....................................................................... 11 

Relation Between Selenium, Mineralogy, and Major Element Oxides Concentrations ............................ 11 

Sulfur, Loss on Ignition, and Selenium in Roof, Parting, and Floor Samples ................................................ 12 

Aqueous Extraction of Soluble Selenium............................................................................................................ 12 

Discussion..................................................................................................................................................................... 14 

Selenium Concentration, Lithology, and Mineralogy ........................................................................................ 14 

Comparison of Se Concentrations in Roof, Parting, Floor, and Four Dominant Lithologies....................... 15 

Mobilization of Soluble Selenium ......................................................................................................................... 16 

Summary and Conclusions ........................................................................................................................................ 16 

References Cited ......................................................................................................................................................... 18

Appendix A1. Coal bed stratigraphy in core USGS 9 

Appendix A2. Coal bed stratigraphy in core USGS 11 

Appendix A3. Coal bed stratigraphy in core USGS 12 

Appendix A4. Lithology terminology and abbreviations used by the West Virginia Geological and 

Economic Survey for core description 

Appendix A5. Geologists’ description of core USGS 9 

Appendix A6. Geologists’ descriptions of core USGS 11 

Appendix A7. Geologists’ descriptions of core USGS 12 

Appendix A8. Natural gamma ray, density, resistivity and caliper logs for core USGS 9 

Appendix A9. Natural gamma ray, density, resistivity and caliper logs for core USGS 11 

Appendix A10. Natural gamma ray, density, resistivity and caliper logs for core USGS 12 

Appendix B1. Se analyses of USGS 9-LITH samples, 1-foot increment samples selected by lithology from 

core USGS 9 

iii
Appendix B2. Se analyses of USGS 9-10-ft samples, 1-foot increment samples collected at 10-foot 

intervals from core USGS 9 

Appendix B3. Se analyses of USGS 11-10-ft samples, 1-foot increment samples collected at 10-foot 

intervals from core USGS 11 

Appendix B4. Se analyses of USGS 12-10-ft samples, 1-foot increment samples collected at 10-foot 

intervals from core USGS 12 

Appendix B5. Major phase mineralogy X-ray diffraction (XRD) and major element oxide X-ray 

fluorescence (XRF) analyses of USGS 9-LITH samples, 1-foot increment samples selected by 

lithology from core USGS 9 

Appendix B6. Major phase mineralogy X-ray diffraction (XRD) and major element oxide X-ray 

fluorescence (XRF) analyses of USGS 9-10-ft samples, 1-foot increment samples collected at 10-

foot intervals from core USGS 9 

Appendix B7. Major phase mineralogy X-ray diffraction (XRD) and major element oxide X-ray 

fluorescence (XRF) analyses of USGS 11-10-ft samples, 1-foot increment samples collected at 10-

foot intervals from core USGS 11 

Appendix B8. Major phase mineralogy X-ray diffraction (XRD) and major element oxide X-ray 

fluorescence (XRF) analyses of USGS 12-10-ft samples, 1-foot increment samples collected at 10-

foot intervals from core USGS 12 

Appendix B9. Se concentration, thickness, ash, total sulfur, and loss on ignition data for roof, parting, 

and floor samples from core USGS 9 

Appendix B10. Se concentration in saturated paste extract leachate (SPE) and rock from USGS 9-10-ft 

samples, 1-foot increment samples collected at 10-foot intervals from core USGS 9 

Appendix B11. Se concentration in saturated paste extract leachates from rock (SPE-A), a second 

extraction (SPE-B), and Se concentration in rock from USGS 11-10-ft samples, 1-foot increment 

samples collected at 10-foot intervals from core USGS 11 

Appendix B12. Se concentration in saturated paste extract leachate (SPE) and rock from USGS 12-10-ft 

samples, 1-foot increment samples collected at 10-foot intervals from core USGS 12 

Appendix B13. Se concentration in sequential water extraction leachate (SWE) and rock from USGS 11-

10-ft samples, 1-foot increment samples collected at 10-foot intervals from core USGS 11 

Appendix B14. Se concentration in replicate analyses of 12 rock samples coincident to both USGS 9-

LITH and USGS 9-10-ft 

Figures 

1. Map showing the location of three widely spaced cores (USGS 9, USGS 11, and USGS 12) in West 

Virginia, used in this study as part of a regional study of geochemical variation in the central 

Appalachian basin ......................................................................................................................................... 20 

2. Se concentration (μg/kg) versus depth (ft) in core USGS 9-LITH samples, 1-foot increment samples 

selected by lithology...................................................................................................................................... 21 

3. Se concentration (μg/kg) versus depth (ft) in core USGS 9-10-ft samples, 1-foot increment samples 

collected at 10-foot intervals ....................................................................................................................... 22 

4. Se concentration (μg/kg) versus depth (ft) in core USGS 11-10-ft samples, 1-foot increment samples 

collected at 10-foot intervals ....................................................................................................................... 23 

5. Se concentration (μg/kg) versus depth (ft) in core USGS 12-10-ft samples, 1-foot increment samples 

collected at 10-foot intervals ....................................................................................................................... 24 

iv
6. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for upper and lower 

stratigraphic intervals in each core ........................................................................................................... 25 

7. Frequency distribution of Se concentration (μg/kg) for all rock samples collected at 10-foot intervals 

from USGS 9-10-ft, USGS 11-10-ft, and USGS 12-10-ft............................................................................ 26 

8. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant lithologies 

from USGS 9-LITH and roof, parting, and floor samples from core USGS 9 ....................................... 27 

9. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant lithologies 

from USGS 9-10-ft and roof, parting, and floor samples from core USGS 9........................................ 28 

10. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant 

lithologies from USGS 9-LITH and USGS 9-RPF (combined roof, parting, and floor samples from 

core USGS 9)................................................................................................................................................... 29 

11. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant 

lithologies from USGS 9-10-ft and USGS 9-RPF (combined roof, parting, and floor samples from 

core USGS 9)................................................................................................................................................... 30 

12. Se concentration (μg/kg) versus siderite (percent) in USGS 9-LITH .......................................................... 31 

13. Se concentration (μg/kg) versus calcite and CaO (percent) in USGS 11-10-ft ......................................... 32 

14. Se concentration (μg/kg) versus chlorite, kaolinite, illite, calcite, and K2

O (percent) in USGS 12-10-ft 33 

15. Se concentration (μg/kg) versus total sulfur (percent, dry basis) in roof, parting, and floor samples 

from USGS 9.................................................................................................................................................... 34 

16. Se concentration (μg/kg) versus loss on ignition (percent, dry basis) in roof, parting, and floor 

samples from USGS 9.................................................................................................................................... 35 

17. Se concentration (μg/L) in saturated paste extract (SPE) versus Se concentration (μg/kg) in rock 

samples from USGS 9-10-ft.......................................................................................................................... 36 

18. Se concentration (μg/L) in saturated paste extract (SPE-A) versus Se concentration (μg/kg) in rock 

samples from USGS 11-10-ft ........................................................................................................................ 36 

19. Se concentration (μg/L) in saturated paste extract (SPE) versus Se concentration (μg/kg) in rock 

samples from USGS 12-10-ft ........................................................................................................................ 37 

20. Se concentration (μg/L) in sequential water extraction first extract (SWE-A) versus Se concentration 

(μg/kg) in rock samples from USGS 11-10-ft ............................................................................................. 37 

21. Se concentration (μg/L) in sequential water extraction first extract of rock sub-sample A (SWE-A) 

versus Se concentration (μg/L) in sequential water extraction first extract of rock sub-sample B 

(SWE-B) for USGS 11-10-ft samples........................................................................................................... 38 

22. Se concentration (μg/L) in saturated paste extract (SPE-A) versus Se concentration (μg/L) in 

sequential water extraction first extract (SWE-A) for duplicate sub-samples of rock from USGS 

11-10-ft ............................................................................................................................................................. 38 

23. Absolute Se (μg Se in solution / kg of rock leached) in saturated paste extract (SPE-A) versus 

absolute Se (μg Se in solution / kg of rock leached) in sequential water extraction first extract 

(SWE-A) for duplicate sub-samples of rock from USGS 11-10-ft.......................................................... 39 

24. Se concentration (μg/L) in sequential water extractions (SWE-) for up to 7 sequential extractions of a 

rock sample, for samples from USGS 11-10-ft.......................................................................................... 40 

Tables 

1. Trace element concentrations for 13 elements, including Se, reported in ASTM 3052 with National 

Institute of Standards and Technology (NIST) data for standard reference material (SRM) 2704 41 

v
2. Comparison of Se concentration in 12 samples coincident to both USGS 9-LITH and USGS 9-10-ft ..... 42 

3. Se concentrations in duplicate samples and replicate analyses of 12 samples coincident to both USGS 

9-LITH and USGS 9-10-ft............................................................................................................................... 44 

4. A test for stratigraphic variation of Se concentration, comparing the upper stratigraphic interval to the 

lower stratigraphic interval in each core (USGS 9-LITH, USGS 9-10-ft, USGS 11-10-ft, and USGS 

12-10-ft), using univariate statistics and t-test comparisons ............................................................. 45 

5. A test for regional variation of Se concentration in each stratigraphic interval (upper and lower) 

compared among cores, using univariate statistics and t-test comparisons .................................... 47 

6. Frequency distribution and univariate statistics for Se concentration data in all samples collected at 

10-foot intervals in USGS 9-10-ft, USGS 11-10-ft, and USGS 12-10-ft................................................... 49 

7. A test for lithologic variation of Se concentration in four dominant lithologies in USGS 9-LITH and 

USGS 9-10-ft samples, using univariate statistics and t-test comparison .......................................... 51 

8. A test for lithologic variation of Se concentration in roof, parting, and floor samples from USGS 9, 

using univariate statistics and t-test comparison.................................................................................... 53 

9. Se concentration in USGS 9-RPF (combined roof, parting and floor samples from USGS 9), univariate 

statistics .......................................................................................................................................................... 54 

10. A test for lithologic variation in Se concentration between USGS 9-RPF, roof, parting, and floor 

samples and four dominant lithologies in USGS 9-LITH and USGS 9-10-ft samples, using 

univariate statistics and t-test comparisons ............................................................................................ 55 

11. Comparison of Se concentrations (ppm) in various lithologies for published data and data reported in 

this study ......................................................................................................................................................... 56 

Conversion Factors 

SI to Inch/Pound 

Multiply By To obtain 

Volume 

Liter (L) 33.82 ounce, fluid (fl. oz) 

Liter (L) 2.113 pint (pt) 

Liter (L) 1.057 quart (qt) 

Liter (L) 0.2642 gallon (gal) 

Liter (L) 61.02 cubic inch (in3

) 

Mass 

Gram (g) 0.03527 ounce, avoirdupois (oz) 

Kilogram (kg) 2.205 pound avoirdupois (lb) 

vi
Selenium Concentrations in Middle Pennsylvanian 

Coal-Bearing Strata in the Central Appalachian Basin 

By Sandra G. Neuzil1, Frank T. Dulong1, C. Blaine Cecil1, Nick Fedorko2, John J. Renton3, and D. K. 

Bhumbla4

Executive Summary 

This report provides the results of a reconnaissance-level investigation of selenium (Se) 

concentrations in Middle Pennsylvanian coal-bearing strata in the central Appalachian basin. 

Bryant and others (2002) reported enrichments of Se concentrations in streams draining areas 

disturbed by surface mining relative to Se concentrations in streams that drain undisturbed areas; 

the study was conducted without the benefit of data on Se concentrations in coal-bearing strata 

prior to anthropogenic disturbance. Thus, the present study was conducted to provide data on Se 

concentrations in coal-bearing strata prior to land disturbance. The principal objectives of this 

work are: 1) determine the stratigraphic and regional distribution of Se concentrations in coalbearing strata, 2) provide reconnaissance-level information on relations, if any, between Se 

concentrations and lithology (rock-type), and 3) develop a cursory evaluation of the leachability of 

Se from disturbed strata. The results reported herein are derived from analyses of samples obtained 

from three widely-spaced cores that were collected from undisturbed rock within a region that has 

been subjected to extensive land disturbance principally by either coal mining or, to a lesser extent, 

highway construction. The focus was on low-organic-content lithologies, not coal, within the coalbearing interval, as these lithologies most commonly make up the fill materials after coal mining or 

in road construction. 

The results and interpretations of the present study are summarized as follows: 

• The precision of the analytical method used in this study to determine Se concentrations in rock 

samples is consistent with the precision as reported by ASTM (The American Society for 

Testing and Materials, ASTM 3052, standard method for the determination of Se in rock 

samples, 95 percent confidence interval (CI 95%) = 0.9 μg/g at the 1 μg/g (1 part per million, 

ppm) level of concentration). The precision of ASTM 3052 is likely to decrease as the 

concentration of Se decreases below 1 μg/g. 

• The average Se concentrations in coal-bearing strata in the central Appalachian basin are 

similar to the average Se concentrations reported for equivalent lithologies (Horn and Adams, 

1966 and references therein). Therefore, the average Se concentrations in the various 

 

1

 U.S. Geological Survey, Reston, Virginia 

2

 West Virginia Geological and Economic Survey, Morgantown, West Virginia (retired 2006) 3

 West Virginia University, Morgantown, West Virginia 

4

 Consultant, Morgantown, West Virginia 

1
lithologies investigated in the present study are not anomalous when compared to values 

reported in the literature. 

• The mean Se concentrations in the higher stratigraphic interval (Stockton A coal bed, lower 

Allegheny Formation, down to the Chilton A coal bed, middle Kanawha Formation) are 

consistently higher than the mean Se concentrations in the lower stratigraphic interval (Chilton 

A coal bed down to the Fire Clay coal bed in the middle Kanawha Formation) in each of the 

three cores that were evaluated. The apparent stratigraphic trend in Se concentrations appears 

to mimic the stratigraphic trend of Se concentrations in coal beds reported by Neuzil and others 

(2005). 

• There is no demonstrable regional variation (trend) in Se concentrations. 

• With the possible exception of higher Se concentration in siltstone, the mean and range of 

selenium concentrations is similar among four dominant lithologies (claystone, shale, siltstone, 

and sandstone). 

• Se concentrations are not consistently correlated with a specific mineral or major element. 

• Se concentrations were determined in selected coal-bed roof, parting, and floor samples from 

one core. The mean values of Se concentrations for each of these three types of samples are 

statistically equal. 

• Se concentrations in the selected roof, parting and floor samples are not statistically correlated 

with total sulfur concentrations (a proxy for the mineral pyrite, FeS2). Therefore, it is unlikely 

that a majority of the Se is associated with pyrite in these samples. 

• Se concentrations in the selected roof, parting, and floor samples correlate with the loss on 

ignition analyses (a proxy for organic matter concentrations). The loss on ignition correlation 

suggests that most of the Se in roof, parting, and floor samples analyzed is organically bonded. 

Rates of organically bonded Se dissolution are likely to be slow and are probably controlled by 

relatively slow rates of chemical oxidation of the host organic matter. 

• Cursory leaching studies indicate that Se concentrations in rock samples are not correlated with 

Se concentrations in water leachates derived from splits of the same rock samples. Therefore, 

total Se, as determined in whole-rock samples, may not be a reliable indicator of water soluble 

Se. Consequently, leach testing, rather than total Se concentrations in rock, may be a more 

useful predictor of potential stream contamination following land disturbance. 

• Although the readily soluble fraction of the total Se in coal-bearing strata is unknown, the 

cursory study of sequential water leaching conducted in the present investigation indicates that 

readily soluble Se may be rapidly removed from rock debris following disturbance of strata. 

On the basis of the present study, the average concentrations of Se in Middle Pennsylvanian 

coal-bearing strata in the central Appalachian basin are not anomalous when compared to published 

values for similar rock types. In addition, the average concentrations of Se indicate that if regional 

trends exist, such trends are below the detection limits of the methods used in this study. Also, 

there is no apparent association of Se with a specific mineral or a specific rock type (claystone, 

shale, siltstone, or sandstone) with the possible exception of Se enrichment in certain siltstone and 

coal-bed roof, parting, and floor samples. Leach testing methods, rather than analyses of total Se 

content of rocks, may provide the most accurate assessment of the potential for Se mobilization and 

stream contamination as a result of land disturbance. 

2
Introduction 

The upper limit of total Se concentration in streams recommended by EPA in order to 

protect aquatic life is 5 micrograms per liter (μg/L, parts per billion, or ppb). Bryant and others 

(2002) reported that concentrations of Se in streams draining areas disturbed by surface mining of 

coal in the central Appalachian basin were higher (median 12 μg/L) in comparison to streams 

draining undisturbed areas (median 1.5 μg/L). However, a general lack of data on Se 

concentrations in coal-bearing strata precluded the attribution of Se concentrations in streams to 

specific rock types, stratigraphic intervals, or specific areas subjected to land disturbance. To 

address any potential correlations between bed rock geology, dissolution of Se following land 

disturbance, and subsequent increases in Se concentrations in streams, the U.S. Geological Survey 

(USGS), in cooperation with the West Virginia Geological and Economic Survey (WVGES) and 

West Virginia University (WVU), initiated a study to evaluate Se concentrations in coal-bearing 

strata (not including the coal beds) in the central Appalachian region. 

In a companion study, Neuzil and others (2005) used data from the USGS National Coal 

Resources Data System to evaluate Se concentrations in Pennsylvanian-age coal beds in the 

Appalachian region. Their study indicates that Se concentrations in Middle Pennsylvanian age coal 

beds (the principal stratigraphic interval of mountain-top-mining at the time of their report) are 

somewhat enriched in Se (median 5 ppm Se, for 737 samples) relative to older and younger coal 

beds (median 3 ppm Se, for 1486 samples). The overall conclusions of the study by Neuzil and 

others (2005) are consistent with earlier observations by Gluskoter and others (1977) that Se is 

enriched in coal beds relative to host strata and relative to the average abundance of Se in the 

earth’s crust. The average Se concentration of upper continental crust is poorly constrained. 

However, Rudnick and Gao (2003) suggest a value of 0.09 ppm Se based on few data. 

Although Se concentrations in coal beds world wide (Yudovich and Ketris, 2006), in the 

United States (Coleman and others, 1993), in eastern Kentucky (Eble and Hower, 1997), and in 

West Virginia (WVGES, 2002) are relatively well known, systematic studies of Se in strata 

associated with coal beds have been minimal. Therefore, the present study was designed to 

develop a preliminary understanding of Se concentrations in coal-bearing strata in the central 

Appalachian basin. This report focuses on Middle Pennsylvanian strata where anthropogenic 

activities such as surface mining and highway construction have either disturbed or may disturb 

large volumes of rock. 

The present study was undertaken to begin developing a data base that can be used in the 

assessment of the effects of land disturbance on Se concentrations in surface streams, as suggested 

by Bryant and others (2002). The current study is a first-stage in the possible development of a 

comprehensive data base, and as such this report is preliminary in nature. Far more data will be 

required in order to conduct a comprehensive assessment of Se concentrations in Pennsylvanian 

age coal-bearing strata, comparable to the report by Neuzil and others (2005) on Se in coal beds. 

The objectives of the present study were to: 1) evaluate the spatial variation of Se, in coal-bearing 

strata in the central Appalachian basin, 2) make a preliminary comparison of Se concentrations in 

coal-bearing strata of the region relative to average concentrations of Se in sedimentary strata, as 

reported in the literature, and 3) investigate the mobilization of Se by water from disturbed coalbearing strata. For the purposes of this report, spatial variation refers to both stratigraphic variation 

and regional variation of Se concentrations in coal-bearing strata. Stratigraphic trends refer to any 

vertical trends in Se concentrations over hundreds of feet of coal-bearing strata. Regional variation 

3
relates to regional trends in Se concentrations over tens to hundreds of square miles. Three widely 

spaced cores that were designated as USGS 9, USGS 11, and USGS 12 were collected, sampled, 

and the samples analyzed, as part of this regional study (fig. 1). The principal coal-bed 

stratigraphic intervals identified in each of the three cores are shown in Appendices A1, A2, and 

A3. The second objective is intended to discern if Se in the coal-bearing strata of the central 

Appalachian region is in any way anomalous when compared to similar sedimentary rocks. The 

third objective is to investigate whether there is any simple analysis that can be used to help predict 

any potential for elevation of Se in streams as a result of land disturbance. 

Acknowledgments 

We thank Arch Coal, Inc. for providing valuable assistance in the field. 

Methods and Analyses 

Coring 

The cores discussed in this report were part of a coring program that was developed to 

evaluate geologic controls on mine-drainage water quality, principally acid drainage. The total 

coring program consisted of eleven cores collected from both the northern- and southern-coal fields 

of West Virginia (fig. 1). One additional core was collected from Pennsylvanian strata in the 

Illinois basin. The cores were designated as USGS cores and they were numbered consecutively 

from one (1) through twelve (12) in the order that they were drilled. Preliminary results of the 

larger acid drainage study can be found in Dulong and others (2002). Cores included in this report 

are limited to those analyzed for Se (USGS 9, USGS 11, and USGS 12). The locations of the three 

cores were selected to provide a cursory evaluation of spatial variations (stratigraphic and regional) 

of Se in Middle Pennsylvanian coal-bearing strata in the central Appalachian basin (fig. 1). All 

three cores intercepted a stratigraphic interval in the Middle Pennsylvanian from the base of the 

Stockton A coal bed in the lower Allegheny Formation to the top of the Fire Clay coal bed in the 

middle Kanawha Formation. All coal beds intercepted in each core are listed in Appendices A1, 

A2, and A3. 

Cores were obtained using standard coal exploratory wireline coring methods, producing a 

nominal 2 inch diameter core. Professional geologists from the WVGES logged all cores in the 

field as they were collected. Lithology terminology and abbreviations, as used by the WVGES for 

lithologic descriptions, are contained in Appendix A4. Core descriptions of USGS 9, USGS 11, 

and USGS 12 are contained in Appendices A5, A6, and A7. In addition, the three core holes were 

logged using standard coal-field geophysical logging that included density and natural gamma ray 

logs for USGS 9 (Appendix A8), USGS 11 (Appendix A9), and USGS 12 (Appendix A10). 

Comparison of geophysical logs with geological logs assured the accuracy of both core recovery 

and depth assignments to specific stratigraphic units such as coal beds. 

Each core of coal-bearing strata was boxed by the geologist on site, and then sent to the 

WVGES core warehouse where they were sampled for Se analyses. Cores of coal beds, including 

partings within the coal beds, as well as six inches of strata above and below the coal (roof-rock 

and floor-rock respectively) were removed from the core at the coring site, placed in core boxes, 

and sent to the WVGES coal laboratory for standard coal analyses. Standard coal analyses by the 

WVGES generally include petrography, elemental analyses, forms of sulfur, and ash content. Coal 

4
analyses are not considered in this report because coal is removed as part of the mining process and 

should not, therefore, represent a significant source of Se in disturbed areas. Occasionally isolated 

blocks of coal in sandstone channel complexes and strata between coal beds may be encountered 

and included in fill material. In the present study the roof, parting, and floor samples from USGS 9 

were analyzed for total sulfur, ash content, and Se content. 

Core Sampling 

Costs prohibited analysis of entire cores. Therefore, sets of samples were selected from the 

cores to assure the following: 1) representative samples of all lithologies were analyzed, 2) samples 

of lithologies were random, and 3) roof, parting, and floor lithologies were adequately sampled. 

Four different sampling protocols were used: 1) selection of one-foot increment samples on the 

basis of lithology (USGS 9), 2) collection of one-foot samples every ten feet (USGS 9, USGS 11, 

and USGS 12), 3) collection of samples of roof, parting, and floor associated with coal-beds 

(USGS 9), and 4) selection of one-foot and partial-foot thick samples close to coal beds (USGS 9). 

The four sampling protocols were used to collect samples from core USGS 9 whereas only the 

second sampling protocol was used to collect samples from cores USGS 11 and USGS 12. 

Samples for analyses were obtained by splitting the core lengthwise with a diamond rock saw and 

taking the appropriate depth increment. 

The first sampling method, used exclusively on core USGS 9, was based on lithologies. 

One hundred (100) one-foot increment samples representing the four principal lithologies of the 

core (9 claystone and mudstone, 20 shale, 23 siltstone, and 48 sandstone) were selected. The 

lithologic description of USGS 9 (Appendix A5) indicates a total thickness of 105 ft claystone and 

mudstone, 235 ft shale, 235 ft siltstone, and 1069 ft sandstone, or a distribution of the four 

lithologies of approximately 6, 14, 14, and 65 percent respectively. The samples selected for 

lithology are referred to as lithology samples, indicated as USGS 9-LITH. This sampling method 

assured that representative samples of the various lithologies, in proportion similar to their 

abundance in the entire core, were analyzed. 

The second core sampling method, which was used on all three cores, consisted of 

collecting a one-foot increment within each ten-foot interval of the core. These samples are 

referred to as increment samples, indicated as USGS 9-10-ft, USGS 11-10-ft, and USGS 12-10-ft 

for the three cores. This method assured randomness of sampling of each core without bias toward 

any parameter except depth from surface. 

The third sampling method involved selection of roof samples (generally six-inch 

increments of strata above coal beds), parting samples (variable thicknesses of rock within coal 

beds), and floor samples (generally six-inch increments of strata below coal beds) from core USGS 

9. These samples, collectively referred to as RPF and indicated as USGS 9-RPF, were intentionally 

biased toward the strata that immediately overlie, are contained within, and underlie coal beds. The 

RPF samples were analyzed in order to evaluate the common perception that coal bed roof, parting, 

and floor strata tend to be relatively enriched in Se. 

The fourth sampling method selected additional samples close to coal beds in core USGS 9. 

Some of these samples were one foot thick (indicated as 1-ft) and some were less than one foot 

thick (indicated as p-ft, for ‘partial-foot’). Throughout this report the 1-ft samples selected close to 

coal beds, as well as the interval samples (one-foot thick sample collected in each ten-foot interval 

5
of the core) are included in USGS 9-10-ft. Occasionally in this report the p-ft samples are also 

included in USGS 9-10-ft data analyses. 

Selenium Analyses of Core Samples 

Each one-foot increment of core was cut longitudinally with a saw so that about one quarter 

of the core was removed. These quarter-core splits were reduced in size to 1⁄4 to 1⁄2 inch pieces with 

a jaw crusher. The resulting material was quartered and three parts archived in plastic sample bags. 

The remaining quarter was further reduced to about 1/8 inch pieces with a mortar and pestle and 

then ground in a shatterbox pulverizer for no more than 5 minutes to a size that passed through a 60 

mesh screen. 

The prepared samples were submitted to the analytical laboratory in the West Virginia 

University, College of Agriculture, Division of Plant and Soil Sciences, where they were analyzed 

for Se using the graphite furnace-atomic absorption (GFAA) method, modified ASTM 3052 [D1] 

(ASTM Method 3052). One quarter gram (0.25 g) of sample was weighed and placed in a 

fluorocarbon reaction vessel with a pressure relief valve fitted with a fluorocarbon membrane. The 

reaction vessel could withstand a pressure of 500 PSI. The sample was then digested in 3 milliliters 

(ml) of hydrofluoric acid (HF) and 9 ml of nitric acid (HNO3

) for 10 minutes in a microwave until 

all material appeared to be in solution. Subsequently, the digestion liquors were treated with 25 ml 

of saturated boric acid solution and then brought to 50 ml total volume by adding distilled water. 

The resultant solution was then filtered through Whatman #42 filter paper and analyzed for Se 

using the graphite furnace-atomic absorption spectrometer equipped with a Zeeman background 

correction system. 

Results of the Se analyses of rock samples from all three cores are shown for USGS 9-LITH

(Appendix B1), USGS 9-10-ft (Appendix B2), USGS 11-10-ft (Appendix B3), and USGS 12-10-ft

(Appendix B4). Selenium determinations that were below the limits of detection (10 μg/kg) were 

reported as ND (not detected). It is a common statistical practice to assign a value equal to half the 

detection limit to samples with analyses below the detection limit. In this report, however, for 

statistical analyses of data sets and graphical illustration, ND data were assigned a value of zero 

(0). A third of the samples have a Se concentration greater than 1,000 μg/kg, which is two orders 

of magnitude greater than the lower detection limit. Thus, whether a value of zero or a value equal 

to half the detection limit (5 μg/kg) is assigned to samples with Se concentration below the 

detection limit will make little difference in statistical calculations and comparisons. The 

difference is discussed further under the heading “Results – Frequency Distribution of Selenium 

Concentrations in All Cores.” 

Analyses of Core Samples for Mineralogy and Major Element Oxides 

A semi-quantitative estimate of the major-phase mineralogy was determined by X-ray 

diffraction (XRD) on all one-foot increment samples at WVU laboratories. The XRD method is 

semi-quantitative. Low values, less than approximately 5 percent, should be used with caution. 

The major mineralogical phases include chlorite, kaolinite, quartz, orthoclase (feldspar), calcite, 

pyrite, siderite, dolomite, illite, and albite (feldspar). In addition to mineralogy, the major element 

oxides were determined by X-ray fluorescence (XRF) at WVU laboratories. XRF is a semiquantitative method. The major oxides include MnO, K2O, SiO2, Al2O3, SO2, Fe2O3, Na2O, 

MgO, TiO2, CaO, and P2O5. Results for XRD mineralogy and XRF major element oxides are 

6
reported for USGS 9-LITH (Appendix B5), USGS 9-10-ft (Appendix B6), USGS 11-10-ft

(Appendix B7), and USGS 12-10-ft (Appendix B8). 

Analyses of Total Sulfur and Loss on Ignition in Coal-Bed Roof, Parting, and Floor Samples 

In addition to standard coal analyses, which include total sulfur (dry basis) and ash (750o C, 

dry basis), the roof, parting, and floor samples from USGS 9 were analyzed for Se content. Loss 

on ignition (LOI) was calculated from percent ash, LOI = (100 – percent ash). Results of the 

analyses of roof, parting and floor samples from USGS 9 are shown in Appendix B9. Coal 

analyses are not considered in this report because coal is removed as part of the mining process, 

and should not represent a significant source of Se in disturbed areas. 

Leach Tests: Saturated Paste Extract (SPE) and Sequential Water Extraction (SWE) 

In addition to the analysis of total Se in selected core samples, some of the ground rock 

samples were analyzed for soluble Se by an adaptation of a method used in analyses of soluble salts 

in soils, a method known as saturated paste extract (SPE) (Rhoades, 1982). The SPE analyses were 

used to estimate the amount of Se that might be available for relatively rapid dissolution following 

land disturbance and reclamation. 

The SPE Se determinations were conducted as follows on samples from USGS 9-10-ft, 

USGS 11-10-ft, and USGS 12-10-ft. A saturation paste of the sample was prepared by adding 11 

ml deionized water to a 50-ml fluorocarbon centrifuge tube and then adding 30 g of sample. The 

mixture was allowed to set overnight, and then shaken for two (2) hours on a wrist-action shaker at 

a speed of 10. After shaking, the mixture was centrifuged at 5000 rpm for 25 minutes in an IESCentram p4r centrifuge. The liquid obtained after centrifugation was filtered through a 0.45 μm 

cellulose nitrate membrane filter. The filtrate was analyzed for Se using the standard GFAA 

method on a Perkin-Elmer 4000 atomic absorption spectrophotometer. Results for the SPE leach 

tests are presented for USGS 9-10-ft (Appendix B10), USGS 11-10-ft (Appendix B11), and USGS 

12-10-ft (Appendix B12). 

A second SPE extraction was conducted on 7 of the 87 samples from USGS 11-10-ft. 

Following the initial saturated paste extract, the residual material was extracted a second time. The 

first extract (SPE) was labeled "A" (SPE-A) and the second extract was labeled "B" (SPE-B) 

(Appendix B11). 

Selected samples from USGS 11-10-ft were subjected to sequential water extraction (SWE) 

of Se. Sequential water extractions were run on 44 fresh samples, designated A, some of which 

were splits derived from samples that were subjected to SPE. For the SWE samples, 10 ml of 

deionized water was added to 5 g of sample. The mixture was allowed to set overnight, and then 

shaken for two hours at a speed of 10 on a wrist-action shaker. The mixture was centrifuged at 

5000 rpm for 25 minutes in an IES-Centram p4r centrifuge, and then filtered through a 0.45 μm 

cellulose nitrate membrane filter. The filtrate was then analyzed. Subsequent sequential 

extractions were conducted by adding an additional 10 ml of water to the solid residue, followed by 

repetition of all other steps, for up to six sequential extractions (2nd through 7th extracts). For 15 of 

the 44 samples, a second split was leached, resulting in analyses of duplicate samples, labeled “B.” 

Results for all SWE analyses for USGS 11-10-ft are presented in Appendix B13. 

7
Results 

Estimates of Analytical Precision 

The American Society for Testing and Materials (ASTM) standard method for the 

determination of Se in rock samples (ASTM 3052 D1) was used in this study. ASTM evaluated the 

95 percent confidence interval (CI 95%) for the method by conducting replicate analyses of 

National Institute of Standards and Testing (NIST) standard reference material (SRM) 2704, 

Buffalo River Sediment. NIST reports a Se concentration of 1.1 μg/g (ppm) in SRM 2704 but does 

not certify this value, possibly because only one analytical method was used to determine Se. 

ASTM analyzed SRM 2704 a number of times for 13 elements, including Se (n = 4), and reported a 

mean Se concentration of 1.13 μg/g (ppm) with a CI 95% of 0.9 μg/g (table 1). Thus, the 

determination of Se by the ASTM 3052 standard method may be relatively imprecise at the 1 μg/g 

(ppm) concentration level and below. 

 

In the present study, the precision of the ASTM 3052 method for the determination of Se 

was estimated on the basis of analyses of replicate samples from USGS 9. Each of 12 one-foot 

increment samples from USGS 9 was analyzed twice, once as part of the lithology sampling, USGS 

9-LITH (Appendix B1), and once as part of the 10-foot increment sampling, USGS 9-10-ft 

(Appendix B2). Inspection of the two sets of analyses indicate that the Se values from USGS 9-

LITH samples are, in general, lower than the Se values for the USGS 9-10-ft samples (table 2). 

As a result of the apparent differences in the duplicate analyses for Se in the twelve 

coincident samples from USGS 9, the twelve coincident samples were used to estimate the 

precision of the analytical method. In order to develop a data set that could be evaluated 

statistically, each of the twelve USGS 9-10-ft samples that was a duplicate of a USGS 9-LITH 

sample was sub-sampled two additional times. These sub-samples were then digested, and each 

digestion was analyzed three times. Thus, each of the twelve USGS 9-10-ft samples was subsampled a total of three times, designated as A, B, and C. The sub-samples were digested and each 

of the digestion liquors was analyzed in triplicate (identified as 1, 2, and 3). The data are shown in 

Appendix B14. 

An estimate of the precision of the ASTM 3052 analytical method was based on statistical 

evaluation of the Se concentration data from three sub-samples and 3 replicate analyses of each 

sub-sample for 12 USGS 9-10-ft samples, which are coincident with 12 samples from USGS 9-

LITH. The mean, standard deviation, number of analyses (N=9), and the 95 percent confidence 

interval (CI 95%) for the mean are shown in table 3 for the 12 coincident samples. A normalized 

metric was calculated in order to compare the 95 percent confidence intervals for mean Se 

concentrations among the 12 coincident samples in USGS 9, where replicate analyses may vary by 

two orders of magnitude (Appendix B14) and mean Se concentrations (table 3) are less than 1000 

μg/kg (1 ppm), with the 95 percent confidence interval reported by ASTM, where the mean Se 

concentration (table 1) is greater than 1 μg/kg (1 ppm). The normalized metric, used here to 

indicate precision of results, is the CI 95% divided by the mean Se concentration, for each sample. 

The CI 95% reported by ASTM was divided by the mean reported by ASTM yielding a value of 

0.80 (table 1). In the present study, for each sample, the CI 95% was divided by the mean and the 

12 resultant values were averaged giving the lab’s precision of the ASTM 3052 method as 0.80 

(table 3). Thus, the precision of analyses by the ASTM 3052 method, estimated by the metric CI 

8
95% / mean in the present study is similar to the precision reported by ASTM, even though the Se 

concentrations are lower in the present study (table 3) compared to the ASTM study (table 1). 

Core Comparisons: a Test for Spatial Variation in Selenium Concentrations in Middle 

Pennsylvanian Coal-Bearing Strata 

A principal objective of the present study was to evaluate spatial variation of Se 

concentrations in coal-bearing strata in the central Appalachian basin. Spatial variation in Se 

concentrations, as used in this report, refers to both stratigraphic variation (vertical trends) and 

regional variation (lateral trends). 

Stratigraphic Variation 

An analysis of stratigraphic variation of Se in Middle Pennsylvanian strata included the 

lower part of the Allegheny Formation down through the middle of the Kanawha Formation 

(Appendices A1, A2, A3). A stratigraphic comparison of Se concentration data was made within 

each of the three cores that were evaluated in the present study. The stratigraphic comparisons 

were based on the mean and 95% confidence interval of two specific stratigraphic intervals in each 

of the three cores. The two stratigraphic intervals were selected on the basis of a visual inspection 

of the data derived from analyses of samples from the first core that was analyzed, USGS 9-LITH 

(fig. 2). Visual inspection of the Se concentration values in USGS 9-LITH indicated that Se 

concentrations were commonly above the limits of detection from the Stockton A coal bed down to 

the Chilton A coal bed, whereas Se concentrations were commonly below the limits of detection 

from the Chilton A coal bed down to the Fire Clay coal bed. Thus, the two stratigraphic intervals 

consist of an upper interval from the base of the Stockton A coal bed down to the top of the Chilton 

A coal bed, and a lower interval from the base of the Chilton A coal bed down to the top of the Fire 

Clay coal bed. The plots of Se concentrations versus depth for the other core data sets are 

presented for USGS 9-10-ft (fig. 3), USGS 11-10-ft (fig. 4), and USGS 12-10-ft (fig. 5). 

The univariate statistics for the two stratigraphic intervals for each core are presented in 

table 4. Comparisons of mean Se concentrations and their respective CI 95% for each stratigraphic 

interval are shown in figure 6 for each core. The rank order of the means of Se concentrations is 

always greater in the upper stratigraphic interval relative to the lower stratigraphic interval (table 

4). However, only in USGS 9 is the mean value for Se concentration in the upper stratigraphic 

interval (from the bottom of the Stockton A coal bed down to the top of the Chilton A coal bed) 

statistically greater than that for the lower stratigraphic interval (from the bottom of the Chilton A 

coal bed down to the top of the Fire Clay coal bed). Statistical analyses of both samplings of 

USGS 9 (-LITH and -10-ft) indicate that the mean Se values in strata overlying the Chilton A Coal 

bed (553 and 666 μg/kg Se, respectively) are greater than the mean Se values in strata that underlie 

the Chilton A coal bed (64 and 329 μg/kg Se, respectively) (table 4). In contrast, based on t-tests, 

there are no statistical differences between the means of Se concentrations in the two stratigraphic 

intervals in either USGS 11-10-ft or USGS 12-10-ft (table 4). The apparent stratigraphic trend in 

Se concentrations in coal-bearing strata, exclusive of coal, in USGS 9 is consistent with 

stratigraphic trends in Se in coal beds as reported by WVGES (2002) for West Virginia and Neuzil 

and others (2005) for the Appalachian Plateau region. Although the rank-order of Se values in the 

upper and lower stratigraphic interval is consistent among the three cores, stratigraphic trends in Se 

concentrations cannot be verified statistically in either USGS 11 or USGS 12 for the stratigraphic 

intervals considered. Thus, a stratigraphic trend in Se concentrations in rock in the Middle 

Pennsylvanian coal-bearing strata cannot be stated with certainty on the basis of the present study. 

9
Regional Variation 

Regional variation was tested on the basis of three cores, USGS 9, USGS 11, and USGS 12 

spaced approximately 50 km apart (fig.1). Regional variation among cores was evaluated by a 

statistical t-test comparison of mean Se concentrations (μg/kg) for each of the two stratigraphic 

intervals. The results are summarized in table 5. The rank order of the mean Se concentrations in 

the upper stratigraphic interval is USGS 9-10-ft > USGS 9-LITH > USGS 12-10-ft > USGS 11-10-

ft. Statistical t-tests show that USGS 9-10-ft is greater than both USGS 12-10 ft and USGS 11-10 

ft and that USGS 9-LITH is greater than USGS 11-10-ft. Otherwise, mean Se concentrations are 

statistically equal. For the lower stratigraphic interval, the rank order of the mean Se 

concentrations is USGS 9-10-ft > USGS 12-10-ft > USGS 11-10-ft > USGS 9-LITH. Statistical ttests show that mean Se concentration in USGS 9-10-ft samples is greater than mean Se 

concentration in USGS 9-LITH samples. All other mean Se concentrations are equal for the lower 

stratigraphic interval. There are no differences in mean Se concentration between any two cores 

that hold for both the upper and lower stratigraphic interval. On the basis of data derived from 

analyses of samples obtained from the three cores that were tested in this study, there are no 

apparent regional variations (trends) in Se concentrations. 

Frequency Distribution of Selenium Concentrations in Three Cores 

The univariate statistics and frequency distribution information for Se concentrations in all 

1-foot increment samples collected at 10-foot intervals (USGS 9-10-ft, USGS 11-10-ft, and USGS 

12-10-ft), are shown in table 6. The Se values for USGS 9-LITH were not used for this analysis 

because of the different sampling method. The two highest Se values, 6820 and 3300 μg/kg, are 

considered high outlier values because they are each approximately twice the value of the next 

highest Se concentration (table 6). These samples were dropped in order to examine the frequency 

distribution of Se concentrations in the remaining 234 samples collected at 10-foot intervals (fig. 

7). Concentrations below the limit of detection (ND) account for 33 percent of all Se concentration 

values. Sixty eight percent of the values are less than 500 μg/kg, and eighty nine percent of the 

values are below 1000 μg/kg. Therefore, the Se data appear to have a log normal distribution, 

which is typical for trace element geochemical data. Whether Se concentrations below the 

detection limit are assigned a value of zero or 5 μg/kg (half the limit of detection), the mean and 

standard deviation change by 2 μg/kg, which is less than 1 percent of the value of the mean and 

standard deviation (table 6). In this study a value of zero was assigned to samples below the 

detection limit, which made little overall difference to the statistics. 

Selenium Concentrations and Dominant Lithologies (Rock Types) 

Four dominant rock types in USGS 9 were sampled for USGS 9-LITH in proportions 

similar to their total thickness in the entire USGS 9 core (Appendix A5). The proportions of the 

four dominant rock types in core USGS 9 and the two sample sets taken from the core are as 

follows: claystone and mudstone, shale, siltstone, and sandstone each represent 6, 14, 14, and 65 

percent of core USGS 9; 9, 20, 23, and 48 percent of samples in USGS 9-LITH; and 14, 5, 10, and 

71 percent of samples in USGS 9-10-ft. The mean Se concentrations and 95 percent confidence 

intervals (μg/kg) within each of the four lithologies were used to evaluate the relation, if any, 

between rock-type and Se concentrations. Univariate statistics and comparisons among dominant 

lithologies were conducted on the two data sets from USGS 9, USGS 9-LITH samples selected by 

lithology and USGS 9-10-ft samples collected every ten feet, and are summarized in table 7. 

10
The mean Se concentration ± the 95 percent confidence interval for the four dominant 

lithologies from USGS 9-LITH and USGS 9-10-ft are shown in figure 8 and figure 9. Among the 

four dominant rock types in the two samplings of USGS 9, the rank order of the mean Se 

concentrations are higher in siltstone than in claystone, shale, or sandstone. However, t-test 

statistical analyses show that only mean Se concentrations in siltstone are higher than in claystone 

for both samplings (table 7). 

Selenium Concentrations in Roof, Parting, and Floor samples 

T-test analyses of the Se concentration data derived from roof (rock immediately above coal 

beds), parting (rock within coal beds), and floor (rock immediately below coal beds) samples from 

USGS 9 indicate that the mean Se concentrations in coal-bed roof, parting, and floor samples are 

statistically equal (table 8). Because the mean Se concentrations in roof, parting, and floor samples 

are equal, the three data sets can be combined and referred to as RPF. The univariate statistics for 

USGS 9-RPF samples are shown in table 9. The mean Se concentration for all USGS 9-RPF 

samples was compared to the mean Se concentrations of the four dominant lithologies data sets 

derived from each of two samplings of USGS 9 (figs. 10 and 11). The statistical t-test comparisons 

of RPF samples with samples of four dominant lithologies in USGS 9-LITH and USGS 9-10-ft are 

summarized in table 10. 

Results show that RPF samples are likely to have Se concentrations that are similar to 

siltstones, but greater than claystones, shales, and sandstones. The statistical similarity between 

RPF samples and shale samples from USGS 9-10-ft is due to the large dispersion of the mean, 

indicated by the large 95 percent confidence interval, for the few (N = 4) shale samples (table 7). 

The statistical t-test evaluation comparing mean Se concentrations separately in each of the 

roof, parting and floor sample data sets with each of the four dominant rock types (lithologies) 

from USGS 9-LITH samples (fig. 8) and USGS 9-10-ft (fig. 9) are summarized in table 10. The 

results are similar to those comparing RPF samples to the four dominant lithologies. Roof and 

floor samples have Se concentrations similar to siltstone samples whereas roof, parting, and floor 

samples have Se concentrations greater than claystone, shale, and sandstone samples for USGS 9-

LITH (fig. 8; table 10). The rank-order of the means for roof, parting, and floor samples and the 

four dominant lithology types of samples from USGS 9-LITH is as follows: parting > floor > roof 

> siltstone > sandstone > shale > claystone (tables 7 and 8). For USGS 9-10-ft, differences in the 

mean Se concentration are not discernible between roof samples and the four dominant lithologies, 

whereas parting and floor samples tend to have Se concentrations greater than claystone and 

sandstone samples and similar to shale and siltstone samples (fig. 9; table 10). The rank order of 

the means for roof, parting, and floor samples and the four dominant lithologies in USGS 9-10-ft is 

as follows: parting > siltstone > floor > roof > sandstone > claystone > shale (tables 7 and 8). 

Relation Between Selenium, Mineralogy, and Major Element Oxides Concentrations 

Pearson’s product moment correlation coefficients were calculated between Se and each 

mineral and major element oxide concentration in each core sampling. Few significant correlations 

(at the 5 percent level of significance) were found. There are no significant correlations of Se with 

pyrite or Fe2

O3 in any of the four core samplings. More than half of the samples in each of the four 

core sample sets have zero values (below detection limit) for calcite, pyrite, and sulfur (Appendices 

B5, B6, B7, B8). 

11
Selenium concentration is significantly correlated with siderite in samples from USGS 9-

LITH (fig. 12). Selenium concentrations for samples from USGS 9-10-ft are not significantly 

correlated with any mineral or major element. 

Se concentrations in samples from USGS 11-10-ft include one point with high Se, calcite, 

and CaO concentrations (Appendices B3 and B7; fig.13). When this high value sample is included 

in the data set, the correlations between Se and calcite and between Se and CaO appear to be 

significant (fig. 13). Upon removal of the data point with high Se, calcite, and CaO, and given that 

most of the samples have calcite concentrations that are below the limit of detection, there is no 

significant correlation between Se and calcite or CaO in USGS 11-10-ft (fig. 13). 

For samples from USGS 12-10-ft, Se is significantly correlated with clay minerals (chlorite, 

kaolinite, and illite), calcite, and K2O (fig. 14). The correlation between Se and chlorite is weak as 

there are many points without detectable Se or measurable amounts of chlorite, and the remainder 

of the points are distributed above and below the trend line. The correlations between Se and 

kaolinite, illite, calcite, and K2O are also weak and thus the concentration of these minerals or K2O 

is not a good predictor of the Se concentration. 

Sulfur, Loss on Ignition, and Selenium in Roof, Parting, and Floor Samples 

The data for coal-bed roof, parting, and floor samples from USGS 9 (Appendix B9) were 

analyzed to determine if there is a significant correlation between Se and total sulfur. The Se 

concentration has a range from below detection to 3340 μg/kg and total sulfur has a range of 0.01 – 

2.22 percent for 26 samples. The results indicate that Se concentrations in the selected roof, 

parting and floor samples do not statistically correlate with total sulfur concentrations (a proxy for 

the mineral pyrite, FeS2

) (fig. 15). Therefore, it is unlikely that a significant portion of Se is 

associated with pyrite in these samples. 

The data for coal-bed roof, parting, and floor samples from USGS 9 were also analyzed to 

determine if there is a significant correlation between Se and organic matter. The loss on ignition 

data, calculated from ash analyses, were used as a proxy for the amount of organic matter. The 

range of loss on ignition is 6 – 48 percent (Appendix B9). Statistical evaluation of the data indicate 

that the Se concentrations in the roof, parting, and floor samples are correlated with the loss on 

ignition at the 5 percent level of significance (R = 0.480, which exceeds the critical value for R(0.05) = 

0.388) (fig. 16). The positive correlation between Se and loss on ignition suggests that Se may 

occur as organically bound Se. 

The statistical comparisons conducted in the present study do not provide an unequivocal 

indication of any relation between Se concentrations and sample mineralogy or sample chemistry. 

The positive correlations that were noted between Se concentrations and sample mineralogy cannot 

be applied with certainty on the basis of the data derived in the present study. Therefore, further 

investigation is needed to determine the mode of occurrence of Se in coal-bearing strata and its 

association with both inorganic and organic material. 

Aqueous Extraction of Soluble Selenium 

There is no generally accepted standard method for the determination of soluble Se in rock 

samples. Therefore, in order to estimate soluble Se in the present study, both the saturated paste 

12
extract (SPE) and sequential water extraction (SWE) methods described above were used to 

evaluate the amount of Se extracted by water. 

The concentration of Se extracted into water from rock, was compared to the total amount 

of Se in the rock. The Se concentration (μg/L or ppb) extracted from rock samples by the SPE 

method was compared to the total Se concentration (μg/kg or ppb) in rock samples from USGS 9-

10-ft (fig. 17), USGS 11-10-ft (fig. 18), and USGS 12-10-ft (fig. 19). The Se concentration (μg/L) 

extracted from rock samples by the SWE method also was compared to the total Se concentration 

(μg/kg) in rock samples from USGS 11-10-ft (fig. 20). In several rock samples, the Se 

concentration is below the detection limit of the GFAA method, yet detectable concentrations of Se 

are leached by SPE or SWE methods. In other cases, high concentrations of Se are measured in 

rock samples yet low concentrations of Se are leached from the rock (figs. 17, 18, 19, 20). Se 

concentrations in SPE leachates from rock do not correlate with Se concentration in the rock in any 

of the three cores (figs. 17, 18, and 19). Furthermore, the Se concentration in leachates from either 

the SPE or the SWE leaching method do not correlate with the Se concentration in the rock in core 

USGS 11 (figs. 18 and 20). 

The reproducibility of water extraction of soluble Se from freshly ground rock samples was 

examined in core USGS 11. Comparison of Se concentration in leachates of duplicate subsamples, SWE-A and SWE-B, give consistent results (fig. 21). It is not clear why Se 

concentrations are higher in SWE-B than in SWE-A in 13 of 15 samples leached in duplicate 

(Appendix B13). In the SWE extractions, two times as much mass of water (10 ml) as rock (5 g) 

was used and each sub-sample was processed in the same way. The correlation coefficient is high 

with an R = 0.9709 for 15 samples (fig. 21). Although SWE leaching is not a standard method to 

determine soluble Se, it appears to give reliable results, and the scatter of data points suggests that 

soluble Se concentrations appear to be reproducible within a factor of two. 

The two methods of extracting soluble Se from rock were compared to determine whether 

the water to rock mass ratio used in the extraction influences either the concentration of Se in the 

water-extract leachate or the amount of Se extracted from the rock. The SPE method used 0.011 L 

water / 0.030 kg rock whereas the SWE method used 0.010 L water / 0.005 kg rock. Thus the SWE 

leach method used 5.4 times more water per kg of rock than the SPE method. The SPE-A and the 

SWE-A extractions, both first extraction leachates, were conducted on 44 duplicate rock samples 

from USGS 11-10-ft. Two observations were made. First, the concentration of Se is higher in 

SPE-A leachates than in SWE-A leachates in 38 of 44 samples (fig. 22) with a high correlation 

coefficient R = 0.8340 that suggests each method gives internally consistent results. The lower Se 

concentrations in SWE-A leachates compared to SPE-A leachates may be a result of dilution by 

more water used per mass of rock leached in the SWE method compared to the SPE method. 

Second, in order to compare the amount of Se leached from rock by the two methods, the 

Se concentrations in SPE-A and SWE-A were normalized to account for the mass of water and 

rock used and is hereafter referred to as “absolute Se” with units of μg Se in solution / kg of rock 

leached. For SPE, the absolute Se is calculated by multiplying the Se concentration in leachate (μg 

Se / kg leachate) by 0.011 kg leachate / 0.030 kg rock and for SWE the absolute Se is calculated by 

multiplying the Se concentration in leachate (μg Se / kg leachate) by 0.010 kg leachate / 0.005 kg 

rock. Comparison of the absolute Se determined for the SWE and SPE methods for USGS 11 

shows that the absolute Se extracted by SWE method is greater than the absolute Se extracted by 

the SPE method in 33 of 44 samples (fig. 23). The slope of the line in figure 23 indicates that the 

13
SWE method extracts twice as much Se from rock as the SPE method. This suggests that the more 

water that comes in contact with rock, the more Se may be leached from the rock. 

Sequential water extractions of Se by the SWE method were conducted in this study to 

determine whether the concentration of Se in leachates changes over time as successive amounts of 

water come into contact with the rock (Appendix B13; fig. 24). The results show that in cases 

where the initial leachate Se concentrations are high, approximately 30 μg/L or higher, there is a 

generally rapid decrease in Se concentrations in successive leachates. After several leaches, 

approximately four, the concentration of Se is lower, generally less than 15 μg/L, and fairly 

constant (fig. 24). 

Discussion 

Selenium Concentration, Lithology, and Mineralogy 

The average Se concentrations in dominant rock types (lithologies) in this study were 

compared with the average Se concentrations in upper continental crust (Wedepohl, 1995; Rudnick 

and Gao, 2003) and sedimentary rocks (Horn and Adams, 1966; Baedecker and others, 1998). The 

average Se concentration in upper continental crust is estimated as 0.083 ppm by Wedepohl (1995) 

and 0.09 ppm by Rudnick and Gao (2003). However, sedimentary rocks only represent a small 

portion, approximately 14 percent, of the upper continental crust (Wedepohl, 1995). Horn and 

Adams (1966) estimated Se concentrations in six sedimentary and marine domains, including shale 

and sandstone, based on iterative geochemical mass balance calculations, starting with a range of 

Se concentrations reported in the literature. Se could not be brought into an internally consistent 

mass balance in the model, probably as a result of significant volcanic input, and should be 

considered as an order of magnitude estimate (Horn and Adams, 1966). The range and calculated 

average Se concentrations for shale and sandstone reported by Horn and Adams (1966) are similar 

to those for the central Appalachian basin shale and sandstone samples analyzed in this study (table 

11). Se concentrations in shale, siltstone, and sandstone samples from the western U.S. are 

reported in the PLUTO data base (Baedecker and others, 1998). Average Se concentrations 

calculated for these western U.S. samples are approximately 5 to 7 times the average Se 

concentrations in shale, siltstone, and sandstone in the central Appalachian basin samples in this 

study (table 11). These comparisons suggest that the Se concentrations in central Appalachian 

sedimentary rocks associated with coal beds are not anomalously high when compared to upper 

continental crust, global estimated average sedimentary rocks, or western U.S sedimentary rocks. 

Several recent studies have examined Se concentrations in various lithologies collected 

from cores drilled in coal-bearing strata in southern West Virginia (Jenkins and Schaer, 2005; 

Mullennex, 2005; Roy, 2005; Vesper and Roy, 2006). Samples in those studies were collected 

from different stratigraphic intervals, selected using different criteria, and categorized into different 

lithologic groups compared to this report. Also, data were presented with different emphases than 

in this report, for example, contrasting samples that were located close to or far from coal beds 

using either 5 ft (Mullennex, 2005) or 2 ft (Vesper and Roy, 2006) as the operational cutoff 

distance. Nevertheless, some general comparisons can be made to data presented in this report. 

Mullennex (2005) sampled 5 cores in one mine in southwestern West Virginia in the stratigraphic 

interval from the No. 6 Block coal, lower Allegheny Formation, down to the Coalburg coal, upper 

Kamawha Formation. This interval partially overlaps the upper part of the “upper stratigraphic 

interval” in this report. Mullennex (2005) presents mean Se concentrations for all shale and all 

14
sandstone, regardless of proximity to coal beds. The mean Se concentrations for all shale and all 

sandstone in USGS 9-10-ft, USGS 11-10-ft, and USGS 12-10-ft core samples (table 11) are within 

a factor of three of those found by Mullennex (2005). Given the differences in sampling protocol 

and stratigraphic interval of Mullennex (2005) and this report, these results are fairly similar. 

The present study evaluated Se concentrations in four rock types (claystone, shale, siltstone, 

and sandstone) in one core, USGS 9, to determine relations, if any, among rock-type and Se 

concentrations. For both USGS 9-LITH and USGS 9-10-ft samples, mean Se concentrations were 

equal in shale and claystone whereas mean Se concentrations in siltstone were greater than 

claystone (table 7). Other comparisons of mean Se concentrations among the lithologies were 

inconsistent from USGS 9-LITH samples to USGS 9-10-ft samples (table 7). 

Mineralogy was determined by X-ray diffraction on all samples in four core sample sets. In 

one core, a correlation was found between siderite and Se whereas in another core, clay minerals 

(chlorite, kaolinite, and illite) correlated with Se. Calcite is below detection in most of the samples. 

In the few samples where calcite is present at high concentrations, the data suggest it may be 

associated with high Se content. There is no correlation between Se and any mineral that holds for 

all cores. Thus, if statistically significant correlations between Se concentrations and mineralogy 

exist, they are below the level of detection by the combined sampling, analytical, and statistical 

methods used in the present study. 

Comparison of Se Concentration in Roof, Parting, Floor, and Four Dominant Lithologies 

Coal-bed roof, parting, and floor samples from core USGS 9 were evaluated to determine 

the relation, if any, between these organic-rich samples that are adjacent to coal beds and their Se 

concentrations. The equality of the mean values and variances for each type of sample were used 

in the comparison. The variances and means are statistically equal among Se concentration for 

roof, parting, and floor samples as shown in table 8. 

Collectively RPF (roof, parting, and floor) samples have mean Se concentrations equal to 

siltstone and greater than claystone and sandstone in core USGS 9 (figs. 10, 11; table 10). Another 

way of stating this is that organic-rich RPF samples located adjacent to coal beds have higher Se 

concentrations than sandstone samples with a distance from coal beds unspecified, for one core 

analysed. Jenkins and Schaer (2005) sampled 7 cores from 3 areas in southern West Virginia in the 

stratigraphic interval from the No. 5 Block coal, lower Allegheny Formation, to the Winifrede coal, 

upper Kanawha Formation. They found higher concentrations of Se in dark organic-rich rock close 

to coal beds compared to sandstone farther from coal beds. Roy (2005) and Vesper and Roy (2006) 

examined one core in the Coalburg through the Winifrede interval in the upper Kanawha 

Formation. Vesper and Roy (2006) and Mullennex (2005) found a trend of more Se in organic-rich 

rock (‘carbolith’ or ‘coal and shale’) than shale than sandstone. The rank order for mean Se 

concentration for USGS 9-LITH was RPF (organic-rich rock close to coal) > sandstone > shale and 

for USGS 9-10-ft RPF > sandstone = shale (tables 7, 10). The difference in the rank order of the 

mean Se concentration of various lithologies (organic-rich rock, shale, and sandstone) compared 

between results found in this report and those published in the literature may be a result of different 

sampling protocols and different stratigraphic intervals examined. 

In this report, the Se concentrations in RPF samples do not correlate with sulfur (a proxy for 

pyrite) but do correlate with loss on ignition (a proxy for organic matter). Similarly, Mullennex 

15
(2005) found no correlation between Se and total, pyritic, or organic sulfur in samples from the No. 

6 Block coal bed through the Coalburg coal bed stratigraphic interval. Roy (2005) and Vesper and 

Roy (2006) did not find any strong correlation between Se and sulfur content or organic matter in 

rock samples. 

Mobilization of Soluble Selenium 

The results of the saturated paste extract (SPE) and sequential water extraction (SWE) 

studies reported herein should be used with caution because standard leaching methods have not 

been developed, nor have definitive Se laboratory leaching studies been conducted. The SPE 

results of this study suggest that total Se in rock is not a predictor for soluble Se. Roy (2005) and 

Vesper and Roy (2006) also noted that soluble Se was not correlated to total Se in rock. SPE or 

some other leaching procedure, rather than total Se values determined on whole-rock samples, may 

provide a more accurate indication of the potential for Se mobilization to streams following land 

disturbance. 

The sequential water extraction (SWE) leaching method used in this study gives results that 

appear to be reproducible within a factor of approximately two (Appendix B13; fig. 21). Given the 

potential for differences in particle sizes, mineralogy, and modes of occurrence of Se in the 

duplicate sub-samples, this reproducibility is fairly good. 

Comparison of the two leaching methods (SPE and SWE) used in this study suggest that the 

more water that comes into contact with rock, such as groundwater flow through rock, (1) the lower 

the concentration of resultant dissolved Se and (2) the more Se will be leached from the rock. In 

disturbed strata, the surface area of rock exposed per mass of rock is almost certainly less than in 

the < 60 mesh rock samples used for SPE and SWE leaching in this study. Therefore, one would 

expect less efficient leaching of Se in disturbed rock strata than in these laboratory studies. 

The sequential leaching studies presented here suggest that Se concentrations of water 

passing through disturbed rock strata may have an initial increase in Se followed by a decrease in 

Se concentrations. Thus, soluble Se may be removed rapidly from disturbed rock strata with 

freshly exposed surfaces. Bonta and Dick (2003) observed an increase in Se concentration in 

streams below coal mining, at three of three mines studied during mining in the northern 

Appalachian basin in Ohio. They found that at one of two coal mines with data after mining, Se 

concentrations decreased to pre-mining levels within 6 years. The sequential leaching studies 

presented here indicate that the “half life” of dissolution of Se from coal-bearing lithologies may be 

relatively short; suggesting that the relative enrichment of Se in streams draining disturbed areas 

may decrease to baseline levels within a relatively few years. 

Summary and Conclusions 

The results and conclusions of the present study are summarized as follows: 

• The precision of the analytical results for total Se in rock samples presented herein are 

consistent with the precision of the analytical method, ASTM 3052, that was used. 

• The average Se concentrations in the four dominant lithologies in coal-bearing strata in the 

central Appalachian basin, as determined in the present study, are similar to the global average 

16
Se concentrations reported for equivalent lithologies (Horn and Adams, 1966) and therefore are 

not anomalous. 

• Rank order of the mean Se concentrations in all coal-bearing lithologies shows that mean Se 

concentrations are higher in upper strata (Stockton A coal bed to Chilton A coal bed) than in 

lower strata (Chilton A coal bed to Fire Clay coal bed) in three widely spaced cores in the 

central Appalachian basin in southern West Virginia. This stratigraphic trend is similar to the 

stratigraphic trend in Se concentrations in coal beds in the central Appalachian basin reported 

by Neuzil and others (2005). 

• On the basis of data derived from analyses of samples obtained from three cores in this study, 

there is no demonstrable regional variation (trend) in Se concentrations. 

• The present study evaluated Se concentrations in a variety of lithologies, rock types, to 

determine relations, if any, among rock-type and Se concentrations. The results indicate that 

average Se concentrations tend to be higher in siltstone compared to claystone, shale, and 

sandstone. When the means and variances of Se concentration are compared in claystone, 

shale, and sandstone, there are no statistically demonstrable differences. If differences exist, 

they are below the limits of verification by the methods used in the present study. 

• Although Se concentrations correlate with some minerals (siderite, chlorite, kaolinite, and illite 

as determined by XRD) in some cores, Se does not consistently correlate with any mineral in 

all cores. 

• Se concentrations were determined in selected coal-bed roof, parting, and floor samples from 

one core. When the data are evaluated statistically, taking into account the mean and variances, 

there are no demonstrable differences in mean Se concentrations among roof, parting, and floor 

samples. 

• Se concentrations do not statistically correlate with total sulfur concentrations suggesting that 

there is not a correlation with pyrite in the selected coal-bed roof, parting, and floor samples. 

However, Se concentrations in the selected coal-bed roof, parting, and floor samples do 

correlate with the loss on ignition, which suggests an association of Se with organic matter. If 

so, rates of mobilization of Se from these organic-rich materials are expected to be controlled 

by relatively slow rates of chemical oxidation of the host organic matter. General principles of 

chemistry suggest that oxidation and dissolution of refractory organic compounds are typically 

quite slow at ambient conditions. 

• The uncertainties associated with the analyses of low concentrations of Se in whole-rock 

samples and the lack of correlation between total Se in rock and susceptibility of Se to 

dissolution suggest that leaching tests, rather than whole-rock analyses, may provide a more 

useful estimation of the potential for Se dissolution and mobilization from coal-bearing strata 

and the potential for increased Se concentrations in surface streams as a result of land 

disturbances. 

• The readily soluble fraction of total Se in coal-bearing strata is not known. However, the 

cursory study of sequential leaching conducted in the present investigation indicates that readily 

soluble Se may be rapidly removed from rock debris following disturbance of strata. It appears 

that the “half life” of dissolution is relatively short, suggesting that any relative enrichment of 

Se in streams draining disturbed areas may decrease to baseline levels within a relatively few 

years after disturbance. Substantiation of the conclusion that Se leaching from disturbed strata 

will have a short half life will require further testing at reclaimed sites. 

17
On the basis of the present study, the average concentrations of Se in Middle Pennsylvanian 

coal-bearing strata in the central Appalachian basin are not anomalous when compared to published 

values of similar rock types. In addition, the average and spread (mean and dispersion) of Se 

concentrations indicate that if either stratigraphic or regional trends exist, such trends can not be 

verified statistically by the methods used herein. Also, there is no apparent association of Se with 

a specific rock type (claystone, shale, siltstone, or sandstone) with the possible exception of Se 

enrichment in certain siltstones. Leaching test methods, rather than total Se content of rocks, may 

more accurately represent the potential for Se mobilization by land disturbance. 

References Cited: 

American Society for Testing and Materials (ASTM), Method 3052, Microwave assisted acid 

digestion of siliceous and organically based matrices, available on the web at: 

http://www.epa.gov/sw-846/pdfs/3052.pdf. 

Baedecker, P.A., Grossman, J.N., and Buttleman, K., 1998, National geochemical data base, 

PLUTO geochemical data base for the United States: U.S. Geological Survey, Digital Data 

Series, DDS 47 (CD-Rom). 

Bonta, J.V., and Dick, W.A., 2003, Impact of coal surface mining and reclamation on surface water 

chemical concentrations and load rates in three Ohio watersheds: Journal of the American Water 

Resources Association, v. 39, no. 4, p. 793-816. 

Bryant, G., McPhilliamy, S., and Childers, H., 2002, A survey of the water quality of streams in the 

primary region of mountaintop / valley fill coal mining, October 1999 to January 2001, in U.S. 

Environmental Protection Agency, Mid Atlantic Region, Mountaintop Mining Environmental 

Impact Statement, Appendix D, Stream chemistry final report, 102 p, available on the web at: 

http://www.epa.gov/region3/mtntop/appendix.htm#appd. 

Coleman, L., Bragg, L.J., and Finkelman, R.B., 1993, Distribution and mode of occurrence of 

selenium in US coals: Environmental Geochemistry and Health, v. 15, p. 215-226. 

Dulong, F.T., Fedorko, N., Renton, J.J., and Cecil, C.B., 2002, Chemical and mineralogical 

analyses of coal-bearing strata in the Appalachian basin. U.S. Geological Survey Open-File 

Report 02-489, available on the web at: http://pubs.usgs.gov/of/2002/of02-489/. 

Eble, C.F., and Hower, J.C., 1997, Coal quality trends and distribution of potentially hazardous 

trace elements in Eastern Kentucky coal: Fuel, v. 76, n. 8, p. 711-715. 

Gluskoter, H.J., Ruch, R.R., Miller, W.G., Cahill, R.A., Dreher, G.B., and Kuhn, J.K., 1977, Trace 

elements in coal; occurrence and distribution: Illinois State Geological Survey Circular, no. 499, 

154 pp. 

Horn, M.K., and Adams, J.A.S., 1966, Computer-derived geochemical balances and element 

abundances: Geochimica et Cosmochimica Acta, v. 30, p. 279-297. 

18
Jenkins, G., and Schaer, N., 2005, The occurrence of selenium in the Upper Kanawha formation of 

the Pennsylvanian system in the southern West Virginia coalfields: West Virginia Department of 

Environmental Protection, available on the web at: 

http://wvmdtaskforce.com/proceedings/05/Jenkins.pdf 

Mullenex, R., 2005, Stratigraphic distribution of selenium in upper Kanawha-lower Allagheny 

formation strata at a location in southwestern West Virginia, presented at the 22nd Annual 

International Pittsburgh Coal Conference, Sept 12-15, 2005, Pittsburgh, Pennsylvania, USA, 

available on the web at: 

http://www.mma1.com/company/pdf/papers/Winter%2005_White%20Paper%20SC.pdf#search=

%22mullennex%20coal%22

National Institute of Standards and Technology (NIST), Standard Reference Material 2704, Buffalo 

River Sediment, National Bureau of Standards Certificate of Analysis, available on the web at: 

http://ts.nist.gov/ts/htdocs/230/232/ARCHIVED_CERTIFICATES/2704.pdf. 

Neuzil, S.G., Dulong, F.T., and Cecil, C.B., 2005, Spatial trends in ash yield, sulfur, selenium and 

other selected trace element concentrations in coal beds in the Appalachian Plateau region, 

U.S.A., U.S. Geological Survey Open-File Report 05-1330, available on the web at: 

http://pubs.usgs.gov/of/2005/1330/. 

Rhoades, J. D., 1982, Soluble salts: in: A. L. Page, R. H. Miller, and D. R. Keeney (editors), 

Methods of soil analysis: Part 2: Chemical and microbiological properties. Monograph Number 9 

(Second Edition). ASA, Madison, Wis., p. 167-179. 

Roy, M., 2005, A detailed sequential extraction study of selenium in coal and coal-associated strata 

from a coal mine in West Virginia: Masters Thesis, West Virginia University, 93 pp. 

Rudnick, R.L., and Gao, S., 2003, The composition of the continental crust: in R.L. Rudnick 

(editor), The Crust: Treatise on Geochemistry (Holland H.D., and Turekian, K.K., eds.), Elsevier, 

Amsterdam, v. 3, p. 1-64, available on the web at: 

http://www.geol.umd.edu/~rudnick/Webpage/Rudnick_Gao_Treatise.pdf#search=%22rudnick%2

0and%20gao%22

Vesper, D.J., and Roy, M., 2006, Selenium location and mode of occurrence in the Kanawha 

Formation rocks in West Virginia: West Virginia Mine Drainage Task Force Symposium, April 

18-19, 2006, Morgantown, West Virginia. 

Wedepohl, K.H., 1995, The composition of the continental crust: Geochimica et Cosmochimica 

Acta, v. 59, n. 7, p. 1217-1232. 

West Virginia Geologic and Economic Survey (WVGES), 2002, Trace elements in West Virginia 

coals - Selenium: available on the web at: 

http://www.wvgs.wvnet.edu/www/datastat/te/SeHome.htm

Yudovich, Y.E., and Ketris, M.P., 2006, Selenium in coal: a review: International Journal of Coal 

Geology, v. 67, p. 112-126. 

19
Figure 1. Map showing the location of three widely spaced cores (USGS 9, USGS 11, and USGS 12, 

indicated by red dots) in West Virginia, used in this study as part of a regional study of geochemical 

variation in the central Appalachian basin. 

20
Figure 2. Se concentration (μg/kg) versus depth (ft) in core USGS 9-LITH samples, 1-foot increment 

samples selected by lithology. 

The interval from the base of the Stockton A coal bed (114 feet) down to the top of the Chilton A coal bed (446 feet) is 

referred to as the upper stratigraphic interval. The interval from the base of the Chilton A coal bed (448 feet) down to 

the top of the Fire Clay coal bed (690 feet) is referred to as the lower stratigraphic interval. One Se value of 2440 

μg/kg at 258-259 feet is larger than the maximum x-scale of 2000 μg/kg Se. 

Data are from Appendix B1. [symbols indicate depth in core and Se concentration of rock samples analyzed; lines 

connecting symbols are for illustration purposes only and do not indicate Se concentrations of rock] 

21
Figure 3. Se concentration (μg/kg) versus depth (ft) in core USGS 9-10-ft samples, 1-foot increment 

samples collected at 10-foot intervals. 

The interval from the base of the Stockton A coal bed (114 feet) down to the top of the Chilton A coal bed (446 feet) is 

referred to as the upper stratigraphic interval. The interval from the base of the Chilton A coal bed (448 feet) down to 

the top of the Fire Clay coal bed (690 feet) is referred to as the lower stratigraphic interval. Two Se values of 3300 

μg/kg at 110.42-110.90 feet, and 6820 μg/kg at 660-661 feet are larger than the maximum x-scale of 2000 μg/kg. 

Data are from Appendix B2. [symbols indicate depth in core and Se concentration of rock samples analyzed; lines 

connecting symbols are for illustration purposes only and do not indicate Se concentrations of rock] 

22
Figure 4. Se concentration (μg/kg) versus depth (ft) in core USGS 11-10-ft samples, 1-foot increment 

samples collected at 10-foot intervals. 

The interval from the base of the Stockton A coal bed (239 feet) down to the top of the Chilton A coal bed (652 feet) is 

referred to as the upper stratigraphic interval. The interval from the base of the Chilton A coal bed (653 feet) down to 

the top of the Fire Clay coal bed (828 feet) is referred to as the lower stratigraphic interval. 

Data are from Appendix B3. [symbols indicate depth in core and Se concentration of rock samples analyzed; lines 

connecting symbols are for illustration purposes only and do not indicate Se concentrations of rock] 

23
Figure 5. Se concentration (μg/kg) versus depth (ft) in core USGS 12-10-ft samples, 1-foot increment 

samples collected at 10-foot intervals. 

The interval from the base of the Stockton A coal bed (316 feet) down to the top of the Chilton A coal bed (492 feet) is 

referred to as the upper stratigraphic interval. The interval from the base of the Chilton A coal bed (493 feet) down to 

the top of the Fire Clay coal bed (625 feet) is referred to as the lower stratigraphic interval. 

Data are from Appendix B4. [symbols indicate depth in core and Se concentration of rock samples analyzed; lines 

connecting symbols are for illustration purposes only and do not indicate Se concentrations of rock] 

24
Figure 6. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for upper and 

lower stratigraphic intervals in each core. 

Data are from table 4. [upper stratigraphic interval (black), lower stratigraphic interval (red)] 

25
Figure 7. Frequency distribution of Se concentration (μg/kg) for all rock samples collected at 10-foot 

intervals from USGS 9-10-ft, USGS 11-10-ft, and USGS 12-10-ft. 

Two high values for Se concentration (3300 and 6820 μg/kg in USGS 9-10-ft) are not included in mean and standard 

deviation calculations or shown on this figure. Bins are labeled by mid-point value, except for first bin (values <50) 

and last bin (values >1800). 

Data are from Appendices B2, B3, and B4 and are summarized in table 6. [StdDev = standard deviation; N = number 

of samples] 

26
Figure 8. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant 

lithologies from USGS 9-LITH and roof, parting, and floor samples from core USGS 9. 

The rank-order of the mean Se concentrations for the seven sample types is: parting > floor > roof > siltstone > 

sandstone > shale > claystone. 

Data are from tables 7 and 8. [CLST = claystone, SH = shale, SLST = siltstone, SS = sandstone] 

27
Figure 9. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant 

lithologies from USGS 9-10-ft and roof, parting, and floor samples from core USGS 9. 

The rank-order of the mean Se concentrations for the seven sample types is: parting > siltstone > floor > roof > 

sandstone > claystone > shale. 

Data are from tables 7 and 8. [CLST = claystone, SH = shale, SLST = siltstone, SS = sandstone] 

28
Figure 10. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant 

lithologies from USGS 9-LITH and USGS 9-RPF (combined roof, parting, and floor samples from core 

USGS 9). 

Statistical t-rests show that the mean Se concentration of RPF (952) is equal to the mean for siltstone (523) and greater 

than the means for claystone (33), shale (65), and sandstone (322). 

Data are from tables 7, 9, and 10. [CLST = claystone, SH = shale, SLST = siltstone, SS = sandstone] 

29
Figure 11. Mean Se concentration (μg/kg) ± 95 percent confidence interval (CI 95%) for four dominant 

lithologies from USGS 9-10-ft and USGS 9-RPF (combined roof, parting, and floor samples from core 

USGS 9). 

Statistical t-tests show that the mean Se concentration of RPF (952) is equal to the means for shale (405) and siltstone 

(943) and greater than the means for claystone (464) and sandstone (467). 

Data are from tables 7, 9, and 10. [CLST = claystone, SH = shale, SLST = siltstone, SS = sandstone] 

30
Figure 12. Se concentration (μg/kg) versus siderite (percent) in USGS 9-LITH. 

Data are from Appendices B1 and B5. 

31
Figure 13. Se concentration (μg/kg) versus calcite and CaO (percent) in USGS 11-10-ft. 

Upon removal of the point with high Se and high calcite the R value becomes 0.0762 and the correlation is no longer 

significant. Upon removal of the point with high Se and high CaO the R value becomes 0.10 and the correlation is no 

longer significant. 

Data are from Appendices B3 and B7. 

32
Figure 14. Se concentration (μg/kg) versus chlorite, kaolinite, illite, calcite, and K2

O (percent) in USGS 

12-10-ft. 

Data are from Appendices B4 and B8. 

33
Figure 15. Se concentration (μg/kg) versus total sulfur (percent, dry basis) in roof, parting, and floor 

samples from USGS 9. 

Data are from Appendix B9. 

34
Figure 16. Se concentration (μg/kg) versus loss on ignition (percent, dry basis) in roof, parting, and 

floor samples from USGS 9. 

Data are from Appendix B9.

35
Figure 17. Se concentration (μg/L) in saturated paste extract (SPE) versus Se concentration (μg/kg) in 

rock samples from USGS 9-10-ft. 

Two high Se values in rock (3300 and 6820 μg/kg) are not plotted and the correlation coefficient (R=0.1334) is not 

significant. If the two high Se values are included, the correlation coefficient is not significant either. 

Data are from Appendices B2 and B10. 

Figure 18. Se concentration (μg/L) in saturated paste extract (SPE-A) versus Se concentration (μg/kg) 

in rock samples from USGS 11-10-ft. 

Data are from Appendices B3 and B11. 

36
Figure 19. Se concentration (μg/L) in saturated paste extract (SPE) versus Se concentration (μg/kg) in 

rock samples from USGS 12-10-ft. 

Data are from Appendices B4 and B12. 

Figure 20. Se concentration (μg/L) in sequential water extraction first extract (SWE-A) versus Se 

concentration (μg/kg) in rock samples from USGS 11-10-ft. 

Data are from Appendices B3 and B13. 

37
Figure 21. Se concentration (μg/L) in sequential water extraction first extract of rock sub-sample A 

(SWE-A) versus Se concentration (μg/L) in sequential water extraction first extract of rock subsample B (SWE-B) for USGS 11-10-ft samples. 

Data are from Appendix B13. 

Figure 22. Se concentration (μg/L) in saturated paste extract (SPE-A) versus Se concentration (μg/L) 

in sequential water extraction first extract (SWE-A) for duplicate sub-samples of rock from USGS 

11-10-ft. 

Data are from Appendices B11 and B13. 

38
Figure 23. Absolute Se (μg Se in solution / kg of rock leached) in saturated paste extract (SPE-A) 

versus absolute Se (μg Se in solution / kg of rock leached) in sequential water extraction first 

extract (SWE-A) for duplicate sub-samples of rock from USGS 11-10-ft. 

Data are calculated from Appendices B11 and B13. 

39
Figure 24. Se concentration (μg/L) in sequential water extractions (SWE-) for up to 7 sequential 

extractions of a rock sample, for samples from USGS 11-10-ft. 

SWE-A is the first extract followed by 2nd, 3rd, 4th, 5th, 6th, and 7th extracts of the same rock 

material. 

Data are from Appendix B13. [claystone = orange, shale = green, siltstone = blue, and sandstone = yellow] 

40
41

Table 1. Trace element concentrations for 13 elements, including Se, reported in ASTM 3052 with 

certification by National Institute of Standards and Technology (NIST) for standard reference 

material (SRM) 2704 

ASTM and NIST report the mean concentration and the 95 percent confidence interval (CI 95%) for each element. A 

normalized metric that is used in this study to indicate precision of results, is the CI 95% divided by the mean 

concentration. Data are from ASTM 3052 (1996), also available on the web at http;//www.epa.gov/sw-846/pdfs/3052.pdf.

[values in parens ( ) are not certified; --- = not analyzed or not reported] 

 

ASTM Analyzed NIST Analyzed ASTM NIST 

Element Count Mean μg/g CI 95% Mean μg/g CI 95% CI÷Mean CI÷Mean 

As 4 23.4 2.6 23.4 0.8 0.11 0.03 

Cd 6 3.5 1.2 3.45 0.22 0.34 0.06 

Cr 6 132.9 1.3 135 5 0.01 0.04 

Cu 6 98.0 4.2 98.6 5.0 0.04 0.05 

Pb 6 155 9.2 161 17 0.06 0.11 

Hg 4 1.49 0.14 1.44 0.07 0.09 0.05 

Ni 6 43.6 3.9 44.1 3.0 0.09 0.07 

P 4 1016 16 998 28 0.02 0.03 

Se 4 1.13 0.9 (1.1) --- 0.80 --- 

S 4 3.56 0.16 --- --- 0.04 --- 

Tl 4 1.15 0.22 1.2 0.2 0.19 0.17 

U 4 2.97 0.04 3.13 0.13 0.01 0.04 

Zn 6 441.9 0.8 438 12 0.002 0.03 

 
Table 2. Comparison of Se concentration in 12 samples coincident to both USGS 9-LITH and USGS 9-10-ft

The table indicates that the Se concentrations for samples selected by lithology (USGS 9-LITH) tend to be lowe

samples collected at 10-foot intervals (USGS 9-10-ft). The correlation coefficient (R = 0.6712) is significant at 

correlation is not significant at the 0.01 level. In order to test the equality of the means (mean Se concentration 

concentration in USGS 9-10-ft), the variances must first be evaluated for equality with an F-test. Depending on the variances are equal (E) or they are unequal (UE). Then a t-test tests for equality of the means (using the appor unequal variances) to determine if the means are equal (E) or unequal (UE). The variance of Se concentratioequal to the variance of Se concentrations in USGS 9-10-ft samples. The mean Se concentration of USGS 9-LISe concentration of USGS 9-10-ft samples. 

[data are from Appendices B1 and B2; StdDev = standard deviation; ND = not detected and a value of 0 was used in calculations] 

USGS 9 

-LITH 

USGS 9 

-10-ft 

USGS 9 

Sample ID -LITH vs Lithology 

interval ft Se μg/kg Se μg/kg 9-10-ft 

163-163 540 740 Lower Siltstone 

170-171 100 700 Lower Siltstone 

280-281 1140 1440 Lower Siltstone 

340-341 640 580 Higher Sandstone 

390-391 480 20 Higher Sandstone 

430-431 ND 400 Lower Sandstone 

460-461 ND ND ND Mudstone 

560-561 380 1520 Lower Shale 

570-571 120 ND Higher Shale 

580-581 ND ND ND Sandstone 

600-601 ND 140 Lower Claystone 

650-651 ND 180 Lower Sandstone 

42
43

Table 2. cont.

USGS 9 

-LITH 

USGS 9 

-10-ft 

Se μg/kg Se μg/kg Compare USGS 9-

Mean 283 477 VaStdDev 361 543 Median 110 290 

Minimum 0 0 Critical Values: F 0.05 (11, 11) = 3.47 and T 0Maximum 1140 1520 Calculated Values: F = 2.262 and T = 1.031 

Count 12 12 Calculated values are < critical values 

CI 95% 204 307 Therefore variances are equal (E) to one anoth
Table 3. Se concentrations in duplicate samples and replicate analyses of 12 

samples coincident to both USGS 9-LITH and USGS 9-10-ft

Three replicate analyses (designated 1, 2, and 3) were conducted on each of 3 sub-samples 

(designated A, B, and C) of 12 samples. The 95 percent confidence interval (CI 95%) is an 

estimate of the precision of the mean Se concentration for the analytical method. The CI 95% 

divided by the mean is a normalized metric that can be used to compare relative dispersion of the 

mean, which can be used to compare the precision of Se concentration measurements for samples 

with differing Se concentrations. 

[calculations use data in Appendix B14; StdDev = standard deviation; count = number of 

analyses; CI 95% = 95 percent confidence interval; CI 95% ÷ Mean = normalized metric used in 

this study] 

 

Sample ID Mean StdDev Count CI 95% CI÷Mean 

Interval ft Se μg/kg 

163-164 453 461 9 301 0.66 

170-171 524 613 9 400 0.76 

280-281 631 515 9 337 0.53 

340-341 149 270 9 176 1.18 

390-391 196 344 9 225 1.15 

430-431 433 628 9 410 0.95 

460-461 269 335 9 219 0.81 

560-561 600 657 9 429 0.72 

570-571 373 437 9 286 0.77 

580-581 329 325 9 212 0.65 

600-601 267 280 9 183 0.69 

650-651 273 288 9 188 0.69 

Mean = 0.80 

 

44
Table 4. A test for stratigraphic variation of Se concentration, comparing the upper stratigraphic 

interval to the lower stratigraphic interval in each core (USGS 9-LITH, USGS 9-10-ft, USGS 11-10-ft, 

and USGS 12-10-ft), using univariate statistics and t-test comparisons

In order to compare the equality of the mean Se concentration in two stratigraphic intervals in each core, the variances 

must first be evaluated for equality with an F-test. Depending on the outcome of the F-test, either the variances are 

equal (E) or they are unequal (UE). Then a t-test is used to test for equality of the means (using the appropriate t-value 

for either equal or unequal variances) and determines if the mean Se concentrations in upper and lower stratigraphic 

intervals are equal (E) or unequal (UE). 

For USGS 9-LITH, the mean Se concentration in the upper interval is greater than in the lower interval (variances are 

unequal to one another and the means are unequal). 

For USGS 9-10-ft, the mean Se concentration in the upper interval is greater than in the lower interval (variances are 

equal to one another whereas the means are unequal). 

For USGS 11-10-ft, the mean Se concentration in the upper interval is equal to the mean Se concentration in the lower 

interval (variances are equal to one another and the means are equal). 

For USGS 12-10-ft, the mean Se concentration in the upper interval is equal to the mean Se concentration in the lower 

interval (variances are equal to one another and the means are equal). 

[calculated from data in Appendices B1, B2, B3, and B4 (with Se values below detection limit set = 0); USGS 9-10-ft 

includes 1-ft samples selected close to coal beds; USGS 9-10-ft lower stratigraphic interval does not include high Se 

value 6820 μg/kg; StdDev = standard deviation; CI 95% = 95 percent confidence interval] 

Upper Stratigraphic Interval (below Stockton A to above Chilton A) 

Core USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 12-10-ft 

Interval 114-446 ft 114-446 ft 239-652 ft 316-492 ft 

Se μg/kg Se μg/kg Se μg/kg Se μg/kg 

Mean 553 666 259 346 

StdDev 456 425 327 335 

Median 480 610 119 320 

Minimum 0 0 0 0 

Maximum 2440 1820 1200 1060 

Count 46 38 41 17 

CI 95% 132 135 100 159 

 

Lower Stratigraphic Interval (below Chilton A to above Fire Clay) 

Core USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 12-10-ft 

Interval 448-690 ft 448-690 ft 653-828 ft 493-625 ft 

Se μg/kg Se μg/kg Se μg/kg Se μg/kg 

Mean 64 329 114 167 

StdDev 163 518 203 264 

Median 0 0 0 10 

Minimum 0 0 0 0 

Maximum 820 1620 540 740 

Count 53 22 18 12 

CI 95% 44 216 94 149 

45
46

Table 4. cont.

 

Compare Upper Stratigraphic Interval versus Lower Stratigraphic Interval 

USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 12-10-ft 

Upper vs Lower Upper vs Lower Upper vs Lower Upper vs Lower 

Variance / Mean Variance / Mean Variance / Mean Variance / Mean 

UE / UE E / UE E / E E / E 

 
Table 5. A test for regional variation of Se concentration in each stratigraphic interval (upper and 

lower) compared among cores, using univariate statistics and t-test comparisons

In order to compare the equality of the mean Se concentration in each stratigraphic interval, the variances must first be evaluated for eDepending on the outcome of the F-test, either the variances are equal (E) or they are unequal (UE). Then a t-test tests for equality of appropriate t-value for either equal or unequal variances) and determines if the mean Se concentrations are equal (E) or unequal (UE). 

For the upper stratigraphic interval: 1) the mean Se concentration in USGS 9-LITH is equal to the mean Se concentration in USGS 9-

(for both comparisons variances are equal to one another and means are equal), and greater than in USGS 11-10-ft (variances are uneq

unequal) 2) the mean Se concentration in USGS 9-10-ft is greater than in USGS 11-10-ft and USGS 12-10-ft (for both comparisons vaanother and the means are unequal); and 3) the mean Se concentration in USGS 11-10-ft is equal to USGS 12-10-ft (variances are equ

means are equal). For the lower stratigraphic interval: 1) the mean Se concentration in USGS 9-LITH is greater than the mean Se concentration in USGunequal, as well as the means), and is equal to the mean Se concentration in USGS 11-10-ft (variances are equal to one another and m12-10-ft (variances are unequal and the means are equal); 2) the mean Se concentration in USGS 9-10-ft is equal to USGS 11-10-ft ancomparisons variances are unequal to one another and the means are equal); and 3) the mean Se concentration in USGS 11-10-ft is eq(variances are equal to one another and the means are equal). [calculated from data in Appendices B1, B2, B3, and B4 (with Se values below detection limit set = 0); USGS 9-10-ft includes 1-ft sa

beds; USGS 9-10-ft lower stratigraphic interval does not include high Se value 6820 μg/kg; StdDev = standard deviation; CI 95% = 9interval] Upper Stratigraphic Interval (below Stockton A to above Chilton A) univariate statistics

Core USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 1

Interval 114-446 ft 114-446 ft 239-652 ft 316-4

Se μg/kg Se μg/kg Se μg/kg Se μ

Mean 553 666 259 346 

StdDev 456 425 327 335 Median 480 610 119 320 Minimum 0 0 0 0 Maximum 2440 1820 1200 1060 

Count 46 38 41 17 CI 95% Table 5 cont. 132 135 100 159 

47
48

Compare Upper Stratigraphic Intervals, F-test / t-test (variance / mean) 

USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 1

USGS 9-LITH -- E / E UE / UE E / USGS 9-10-ft -- -- E / UE E / 

USGS 11-10-ft -- -- -- E / 

Lower Stratigraphic Interval (below Chilton A to above Fire Clay) univariate statistics

Core USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 1

Interval 448-690 ft 448-690 ft 653-828 ft 493-6

Se μg/kg Se μg/kg Se μg/kg Se μ

Mean 64 329 114 167 

StdDev 163 518 203 264 

Median 0 0 0 10 

Minimum 0 0 0 0 

Maximum 820 1620 540 740 

Count 53 22 18 12 CI 95% 44 216 94 149 Compare Lower Stratigraphic Intervals, F-test / t-test (variance / mean) 

USGS 9-LITH USGS 9-10-ft USGS 11-10-ft USGS 1

USGS 9-LITH -- UE / UE E / E UE USGS 9-10-ft -- -- UE / E UE 

USGS 11-10-ft -- -- -- E / 
Table 6. Frequency distribution and univariate statistics for Se concentration data in all samples 

collected at 10-foot intervals in USGS 9-10-ft, USGS 11-10-ft, and USGS 12-10-ft 

A. Univariate statistics are calculated for all Se concentrations. 

B. Univariate statistics are calculated for Se concentrations without the two highest Se values. 

C. Univariate statistics are calculated for Se concentrations without the two highest Se values and replacing 0 values 

(not detected) with 5 (half the detection limit). 

[calculated from data in Appendices B2, B3, and B4 (with Se values below detection limit set = 0 unless otherwise 

noted); USGS 9-10-ft includes 1-ft and p-ft samples (see Appendix B2); StdDev = standard deviation; CI 95% = 95 

percent confidence interval] 

Se Frequency Percent Cumulative 

μg/kg Percent 

0 78 33.1 33.1 

10 2 0.8 33.9 A. All Data 

20 5 2.1 36.0 Se μg/kg 

54 1 0.4 36.4 Mean 406 

60 4 1.7 38.1 StdDev 628 

80 2 0.8 39.0 Median 200 

90 1 0.4 39.4 Minimum 0 

100 6 2.5 41.9 Maximum 6820 

115 1 0.4 42.4 Count 236 

119 1 0.4 42.8 CI 95% 80 

120 2 0.8 43.6 

124 1 0.4 44.1 B. Remove 2 high Se values (6820 and 3300) 

140 3 1.3 45.3 Se μg/kg 

160 3 1.3 46.6 Mean 366 

180 5 2.1 48.7 StdDev 428 

193 1 0.4 49.2 Median 200 

200 3 1.3 50.4 Minimum 0 

220 3 1.3 51.7 Maximum 1840 

233 1 0.4 52.1 Count 234 

240 1 0.4 52.5 CI 95% 55 

260 1 0.4 53.0 

272 1 0.4 53.4 

C. Remove 2 high Se values (6820 and 3300) and 

change 0 values to 5 

280 1 0.4 53.8 

285 1 0.4 54.2 Se μg/kg 

300 3 1.3 55.5 Mean 368 

320 5 2.1 57.6 StdDev 427 

340 2 0.8 58.5 Median 200 

355 1 0.4 58.9 Minimum 5 

360 3 1.3 60.2 Maximum 1840 

371 1 0.4 60.6 Count 234 

380 1 0.4 61.0 CI 95% 55 

400 6 2.5 63.6 

413 1 0.4 64.0 

420 1 0.4 64.4 

440 2 0.8 65.3 

460 2 0.8 66.1 

480 3 1.3 67.4 

500 2 0.8 68.2 

49
520 2 0.8 69.1 

540 2 0.8 69.9 

560 4 1.7 71.6 

580 3 1.3 72.9 

600 5 2.1 75.0 

620 1 0.4 75.4 

640 1 0.4 75.8 

660 4 1.7 77.5 

680 1 0.4 78.0 

700 3 1.3 79.2 

708 1 0.4 79.7 

720 1 0.4 80.1 

739 1 0.4 80.5 

740 3 1.3 81.8 

760 1 0.4 82.2 

777 1 0.4 82.6 

780 1 0.4 83.1 

800 3 1.3 84.3 

820 1 0.4 84.7 

840 2 0.8 85.6 

860 1 0.4 86.0 

900 2 0.8 86.9 

940 2 0.8 87.7 

960 2 0.8 88.6 

980 1 0.4 89.0 

1000 1 0.4 89.4 

1040 3 1.3 90.7 

1060 1 0.4 91.1 

1080 1 0.4 91.5 

1100 1 0.4 91.9 

1140 2 0.8 92.8 

1200 2 0.8 93.6 

1240 2 0.8 94.5 

1260 1 0.4 94.9 

1320 1 0.4 95.3 

1380 1 0.4 95.8 

1440 1 0.4 96.2 

1500 1 0.4 96.6 

1520 2 0.8 97.5 

1540 1 0.4 97.9 

1620 1 0.4 98.3 

1820 1 0.4 98.7 

1840 1 0.4 99.2 

3300 1 0.4 99.6 

6820 1 0.4 100.0 

Total 236 100.0 

 

50
Table 7. A test for lithologic variation of Se concentration in four dominant lithologies in USGS 9-

LITH and USGS 9-10-ft samples, using univariate statistics and t-test comparison 

The four dominant lithologies are claystone (CLST), shale (SH), siltstone (SLST), sandstone (SS). 

Rank order of means in USGS 9-LITH is SLST > SS > SH > CLST. T-test comparison of mean Se concentrations 

among lithologies in USGS 9-LITH is as follows: CLST = SH, CLST < SLST, CLST < SS, SH < SLST, SH < SS, 

SLST = SS. 

Rank order of means in USGS 9-10-ft is SLST > SS > CLST > SH. T-test comparison of mean Se concentration 

among lithologies in USGS 9-10-ft is as follows: CLST = SH, CLST < SLST, CLST = SS, SH = SLST, SH = SS, 

SLST > SS. 

[calculated from data in Appendices B1 and B2 (with Se values below detection set = 0); USGS 9-10-ft includes 1-ft 

samples and does not include high outlier Se = 6820 μg/kg in a sandstone sample; StdDev = standard deviation; CI 

95% = 95 percent confidence interval] 

 

USGS 9-LITH, univariate statistics 

Claystone Shale Siltstone Sandstone 

Se μg/kg Se μg/kg Se μg/kg Se μg/kg 

Mean 33 65 523 322 

StdDev 100 144 605 333 

Median 0 0 400 250 

Minimum 0 0 0 0 

Maximum 300 540 2440 1000 

Count 9 20 23 48 

CI 95% 65 63 247 94 

 

USGS 9-LITH, F-test / t-test 

 Variance / Mean 

Shale Siltstone Sandstone 

Claystone E / E UE / UE UE / UE 

Shale -- UE / UE UE / UE 

Siltstone -- -- UE / E 

 

51
Table 7. cont. 

USGS 9-10-ft, univariate statistics 

Claystone Shale Siltstone Sandstone 

Se μg/kg Se μg/kg Se μg/kg Se μg/kg 

Mean 464 405 943 467 

StdDev 506 745 547 395 

Median 200 50 740 400 

Minimum 0 0 320 0 

Maximum 1320 1520 1820 1620 

Count 10 4 7 52 

CI 95% 314 730 405 107 

 

USGS 9-10-ft, F-test / t-test 

 Variance / Mean 

Shale Siltstone Sandstone 

Claystone E / E E / UE E / E 

Shale -- E / E UE / E 

Siltstone -- -- E / UE 

 

52
Table 8. A test for lithologic variation of Se concentration in roof, 

parting, and floor samples from USGS 9, using univariate 

statistics and t-test comparisons 

The means are equal to one another for the 3 sample groups: roof = parting 

= floor. 

[calculated from data in Appendix B9; StdDev = standard deviation; CI 95% 

= 95 percent confidence interval] 

 

Univariate Statistics 

Roof Parting Floor 

Se μg/kg Se μg/kg Se μg/kg 

Mean 798 1280 922 

StdDev 732 649 1020 

Median 550 1180 600 

Minimum 140 500 0 

Maximum 1940 2300 3340 

Count 8 5 13 

CI 95% 507 569 555 

 

F-test / t-test 

Variance / Mean 

Parting Floor 

Roof E / E E / E 

Parting -- E / E 

 

53
Table 9. Se concentration in USGS 9-RPF (combined roof, 

parting and floor samples from USGS 9), univariate statistics 

[calculated from data in Appendix B9; StdDev = standard deviation; CI 

95% = 95 percent confidence interval] 

 

Univariate Statistics 

RPF 

Se μg/kg 

Mean 952 

StdDev 864 

Median 660 

Minimum 0 

Maximum 3340 

Count 26 

CI 95% 332 

 

54
Table 10. A test for lithologic variation in Se concentration between USGS 9-RPF, 

roof, parting, and floor samples and four dominant lithologies in USGS 9-LITH and 

USGS 9-10-ft samples, using univariate statistics and t-test comparisons 

RPF = combined roof, parting, and floor samples. The four dominant lithologies are claystone (= 

CLST), shale (= SH), siltstone (= SLST), and sandstone (= SS). 

In USGS 9-PRF and USGS 9-LITH, rank order of the mean Se concentrations is RPF > SLST > SS 

> SH > CLST. T-test comparison of mean Se concentrations among RPF and dominant lithologies 

in USGS 9-LITH is as follows: RPF > CLST, RPF > SH, RPF = SLST, RPF > SS. 

In USGS 9-PRF and USGS 9-10-ft, rank order of the mean Se concentrations is RPF > SLST > SS 

(without high Se value = 6820 μg/kg) > CLST > SH. T-test comparison of mean Se concentrations 

among RPF and dominant lithologies in USGS 9-10-ft is as follows: RPF > CLST, RPF = SH, RPF 

= SLST, RPF > SS. 

[calculated from data in tables 7, 8, and 9] 

 

USGS 9-LITH, F-test / t-test 

Variance / Mean 

Claystone Shale Siltstone Sandstone 

RPF UE / UE UE / UE E / E UE / UE 

roof UE / UE UE / UE E / E UE / UE 

parting UE / UE UE / UE E / UE UE / UE 

floor UE / UE UE / UE UE / E UE / UE 

 

USGS 9-10-ft, F-test / t-test 

Variance / Mean 

Claystone Shale Siltstone Sandstone 

RPF UE / UE E / E E / E UE / UE 

roof E / E E / E E / E UE / E 

parting E / UE E / E E / E E / UE 

floor UE / E E / E E / E UE / UE 

 

55
Table 11. Comparison of Se concentrations (μg/g or ppm) in various lithologies for published 

data and data reported in this study

 

Claystone Shale Siltstone Sandstone 

 Se μg/g Se μg/g Se μg/g Se μg/g 

Horn and Adams (1966), modeled global average 

Mean 0.60 0.525 

Minimum 0.3 0.05 

Maximum 0.9 1.0 

 

Baedecker and others (1998), western US (see notes below) 

Mean 2.9 2.6 1.5 

StdDev 5.7 5.9 7.3 

Median 0.70 0.70 0.10 

Minimum 0.05 0.10 0.05 

Maximum 34 23 100 

Count 247 23 672 

CI 95% 0.72 2.4 0.56 

 

Mullennex (2005), 5 cores at a mine site in southwest West Virginia 

Mean 0.75 0.09 

StdDev 1.23 0.11 

Count 102 211 

CI 95% 0.24 0.01 

 

This Study (data from Appendices B2, B3, B4), 3 cores (USGS 9-10-ft, 11-10-ft, 12 -10-ft) from southwest West 

Virginia [USGS 9-10-ft includes 1-ft and p-ft samples; does not include two high Se values 6.82 and 3.30 ppm 

in sandstone] 

Mean 0.46 0.42 0.56 0.32 

StdDev 0.49 0.44 0.56 0.40 

Median 0.20 0.32 0.41 0.16 

Minimum 0.00 0.00 0.00 0.00 

Maximum 1.32 1.52 1.82 1.84 

Count 15 33 20 166 

CI 95% 0.25 0.15 0.25 0.06 

 

Data from Baedecker and others (1998): 

1) 1439 data points, all shale and sandstone data with Se values 

2) Samples are from western US, including Alaska 

3) Use Geolex (http://ngmdb.usgs.gov/Geolex/geolex_home.html) to determine usage and 

age range for given information on Formations 

4) Assign dominant lithology and lithologic modifier from Appendix A4. 

5) Negative values are ‘less than’ values. 

6) Assign the value 0.05 ppm to all negative Se values (289). 0.05 ppm is the absolute value 

of half the median value for all ‘less than’ values. 

56
Table 11. cont. 

Remove 497 samples: 

1) Samples with “no information” for Formation (16) 

2) Samples with Pre Cambrian for age (217) 

3) Samples with ROOF, PART (parting), and SEAT (floor) for lithology associated with coal 

beds (all 19 samples from Alaska) 

4) Samples with ROCK (no specific lithology information), SURF MAT (surface material), 

PYR (pyrite), BREC (breccia), CGL (conglomerate), LS (limestone), and CLST (claystone) 

for lithology (87) 

5) Samples with lithologic modifier of ORE (ore), U (uranium mineralization), MIN 

(mineralization, usually sulfate), FEST (ironstone - goethite mineralization), and PYR 

(pyrite) (158) 

The resultant data set, used above, is 942 samples: 

857 range in age from Tertiary to Mississippian 

85 sandstone samples (75 are from Utah) have no age data (no Formation given) 

 

57