Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
POTENTIAL USE OF WEATHERED SANDSTONES TO CONSTRUCT A
LOW PERMEABILITY BARRIER TO ISOLATE PROBLEMATIC COAL
MINE SPOILS1
Mariana da Rosa2, Carmen T. Agouridis, and Richard C. Warner
Abstract. Specific conductance and selenium (Se) are two water quality parameters of
emerging concern in the Appalachian coalfields. Isolation of high specific conductance
and Se producing spoils from environmental water flows using a low permeability barrier
is one method of minimizing the leaching of these constituents from coal mine spoils.
Ideally, the material used to form the barrier should be readily accessible, have low levels
of specific conductance and Se, and be capable of achieving a low permeability with the
proper moisture adjustment. Brown and gray weathered sandstones are often readily
available at mine sites in the Appalachian coalfields. Spoil samples and water quality
samples from the University of Kentucky Bent Mountain Research Complex near
Pikeville, Kentucky indicated that these spoil types hold promise in meeting the criteria
of being a low specific conductance producing material. However, these sandstones tend
to have higher sand contents than those typically used in compacted barriers or liners in
landfills. The objective of this study was to assess the potential of using brown and/or
gray weathered sandstones to create a low permeability barrier. To meet the objective of
the study, a total of four spoil samples (identified as M1-M4) were collected in 2012.
Each spoil sample was obtained from a different mine in eastern Kentucky. Samples M1
and M2 consisted of brown sandstone; sample M3 was gray sandstone; and sample M4
was a mixture of brown and gray sandstones. Each spoil sample was screened and
analyzed for soil texture. Spoil moisture content-density relationships and spoil saturated
hydraulic conductivity-moisture content relationships were developed for each sample
using double ring permeameters. Maximum saturated hydraulic conductivity values
ranged between a low of 5.9 x 10-8 cm s-1 to a high of 3.1 x 10-7 cm s-1 in the laboratory
for the <2mm fraction. These saturated hydraulic conductivity values were comparable
to soils used to construct liners in landfills, particularly in instances where the percentage
of fines in the spoils were about 50% or greater. When in the field, however, it is
expected that these saturated hydraulic conductivity values will typically be 1-3 orders of
magnitude higher due to rock fragments. These results demonstrate that brown
sandstone, with its higher fines content, is likely a more suitable media than gray
sandstone for constructing a low permeability barrier to isolate high specific conductance
producing and/or Se generating spoils. Based on these laboratory results, field
assessments of brown weathered sandstones for this application are recommended.
Additional Key Words: Proctor density, hydraulic conductivity, water quality.
___________________
1
Oral paper presented at the 2013 National Meeting of the American Society of Mining and Reclamation,
Laramie, WY Reclamation Across Industries, June 1–6, 2013 and accepted for the online Journal of
The American Society of Mining and Reclamation, Volume 2, No. 1, 2013. R.I. Barnhisel (Ed.).
Published by ASMR, 3134 Montavesta Rd., Lexington, KY 40502
2
Mariana da Rosa is an Undergraduate Research Assistant in Agricultural Engineering Department,
Universidade Federal de Viçosa, Viçosa, Brazil; Carmen T. Agouridis is an Assistant Professor,
Biosystems and Agricultural Engineering Department, University of Kentucky, Lexington, KY 40546;
and Richard C. Warner is an Extension Professor, Biosystems and Agricultural Engineering
Department, University of Kentucky, Lexington, KY 40546.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
Introduction
Surface mining practices such as contour and area mining have been linked to elevated levels
of specific conductance and selenium (Se) (Fritz et al., 2010; Lindberg et al., 2011), which are
two constituents of emerging concern in the Appalachian coalfields. During the mining process,
consolidated rock above the coal seams are subjected to blasting resulting in many smaller more
weatherable particles, some of which are high in sulfur and/or Se (Vesper et al., 2008; Barton,
2011). Research has shown that high specific conductance and Se levels in mine drainage waters
negatively impact aquatic communities. Pond et al. (2008) found notably fewer Ephemeroptera
taxa in streams in the Appalachian coalfields when specific conductance levels were above
500 μS cm-1. Selenium, while an essential trace element, is toxic to fish at high levels (Janz,
2012). Chronic exposure to elevated levels of Se, particularly in the early stages of life, can
result in fish deformities or death (Hamilton, 2004; Janz, 2012). In response to such findings
regarding specific conductance, the U.S. Environmental Protection Agency (USEPA) issued
guidance in 2011 stating that waters discharged from mined lands in this region should have
specific conductance levels no greater than 300-500 μS cm-1 (USEPA, 2011b). USEPA (2011a)
recommended the lower limit of 300 μS cm-1 as this was the level at which “5% of native
macroinvertebrate genera are extirpated,” which is the endpoint typically used when establishing
a numeric criteria for protecting aquatic life, while the upper limit of 500 μS cm-1 was based
upon the findings of Pond et al. (2008). This guidance was struck down by the U.S. District
Court for the District of Columbia on July 2012 for violating rulemaking procedures outlined in
the Administrative Procedure Act (National Mining Association v. Jackson, D.D.C., No. 1:10-cv1220, 7/31/12) (Kovski, 2012). However, on May 7, 2013, the USEPA was delivered a formal
petition requesting that they begin the rule-making process to establish a specific conductance
standard for streams affected by mountaintop mining (Ward, 2013) meaning that the issues
surrounding specific conductance and coal mining are not yet resolved. As for Se, the USEPA
has a freshwater chronic water quality guideline of 5 μg L-1.
It is theorized that reclamation techniques, such as the Forestry Reclamation Approach
(FRA) which promotes the creation of a suitable root medium for good tree growth (e.g. topsoil,
weathered sandstone, and/or the best available material) and hence reforestation, will help
mitigate the impacts of surface mining on water quality (Burger et al., 2005; Zipper et al., 2011;
Agouridis et al., 2012). Specific conductance levels in grab samples collected from test plots of
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
brown weathered sandstone, gray unweathered sandstone, and a mixture of the two and shale
were below 500 μS cm-1 after three years (Agouridis et al., 2012) which is a relatively short time
period considering that Fritz et al. (2010) measured specific conductance values between 2,000
and 3,000 μS cm-1 down-gradient of valley fills older than 10 years. While Agouridis et al.
(2012) showed that a reduction in the specific conductance levels of waters discharged from
spoil placed in accordance with the FRA occurred, the cause of this reduction is not certain. It is
possible that the thickness of the spoil (approximately 2.5 m) influenced specific conductance
levels as salts were flushed from the spoil over the study period. Less thick spoils may flush
salts more quickly while a longer period of time may be required to reach the same specific
conductance levels for thicker spoils. To date, the FRA has not been evaluated as a mechanism
to reduce Se concentrations in mine discharged waters.
While it is important to note the mitigating effects of the FRA, it is also important to note the
timeline in which these effects are realized.
As noted by Barton (2011), one significant
challenge is maintaining water quality standards during the active mining practice. Warner and
Agouridis (2010) recommended the use of source reduction techniques whereby highconductivity and high-Se producing materials are isolated from infiltrating waters through the
use of a low permeability barrier. The technique of isolating materials with such a barrier is
common in landfill operations (Goldman et al., 1988) and in coal mining operations which
encounter acid-forming strata (Skousen et al., 2000; Johnson and Hallberg, 2005). However, in
landfill operations, the barrier is typically created using clay which is difficult to locate in the
sandstone geology of the Appalachian coalfields. While the literature is plentiful regarding the
saturated hydraulic conductivity of clayey soils (e.g. Olson and Daniel, 1981; Goldman et al.,
1988; Kang and Shackelford, 2010), a void exists regarding materials with higher sand contents
such as weathered sandstone spoils. The question remains regarding whether or not these
weathered brown and gray sandstone spoils, which have high sand contents (Emerson et al.,
2009; Agouridis et al., 2012), have a sufficient percentage of fines (e.g. silt and clay) in the
overall rock content to create a low permeability barrier when compacted or if an amendment or
alternate material is needed. The objective of this study was to measure maximum density and
saturated hydraulic conductivity of brown, gray, and a combination of brown and gray weathered
sandstones to assess their potential for use in constructing a low permeability barrier to isolate
problematic spoils.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
Methods
Study Sites
Spoil samples were collected in August 2012 from four surface mines located in the
Appalachian coalfields of eastern Kentucky (Fig. 1). Because of confidentiality agreements, we
are not permitted to reveal the exact locations of the mines. All of the surface mines are located
in the Cumberland Plateau Physiographic region, which is a predominately forested region in
eastern Kentucky. The climate in this region is humid and temperate. Based on the National
Oceanic and Atmospheric Administration (NOAA) weather station located in Jackson,
Kentucky, which is central to three of the four mines, average annual rainfall is 125 cm.
Temperatures range from a low of -4°C in the winter months to a high of 32°C in the summer
months.
The geologic unit of all four mines was the Lower and Middle Pennsylvanian Breathitt
formation. One sandstone sample was collected at each of the mines, which are referred to as
Mine 1 (M1), Mine 2 (M2), Mine 3 (M3), and Mine 4 (M4) (Table 1) in this paper. The sample
from M1 was associated with the Lower Richardson coal seam, and it consisted of 100% brown
sandstone that was collected from the top 2 m below a shallow soil layer. The sample from M2
was associated with the Middle Peach Orchard coal seam, and it consisted of 100% brown
sandstone that was collected from the top 1.2 m below a shallow soil layer. The samples from
M3 and M4 were associated with the Hazard 7, 8, and 9 coal seams. Sample M3 consisted of
100% gray sandstone located immediately below a brown sandstone layer while sample M4 is
50% brown sandstone and 50% gray sandstone (visual approximation made by personnel in the
Virginia Tech University Department of Crop and Soil Environmental Sciences). The mixture of
brown and gray sandstones (M4) was tested as this represents the condition in which the mine
operator acquires spoil at a greater depth below the surface (e.g. 1-4 m). Spoil samples were
placed in 19 L buckets and sealed for transport to the University of Kentucky Biosystems and
Agricultural Engineering Department for analysis.
Spoil Characterization
Three subsamples of each spoil (M1, M2, M3, and M4) were taken to the University of
Kentucky Regulatory Services (UKRS) and analyzed for percent sand, silt and clay using the
micro-pipette method (Miller and Miller, 1987; Burt et al., 1993). For this analysis, subsamples
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
Figure 1. Approximate locations of the surface mines sampled in eastern Kentucky. Numbers 1,
2, 3, and 4 correspond to the mine codes (and sample codes) Mine 1 (M1), Mine 2
(M2), Mine 3 (M3), and Mine 4 (M4).
Table 1. Coal seams associations and spoil types for each sample.
Sample
M1
M2
M3
M4
Coal Seam
Lower Richardson
Middle Peach Orchard
Hazard 7, 8 and 9
Hazard 7, 8 and 9
Spoil Type
100% brown sandstone
100% brown sandstone
100% gray sandstone
50% brown sandstone and 50% gray sandstone1
1
Visual assessment performed by personnel in the Virginia Tech University Department of Crop and Soil
Environmental Sciences.
were classified using the United States Department of Agriculture (USDA) textural triangle
(USDA-NRCS, 2012) and compared using a completely randomized design (PROC GLM) in
SAS (SAS Institute, 2008). The liquid limit, plastic limit, and plasticity were each ground and
passed through a 2 mm sieve by UKRS. Any fragments >2 mm were discarded. Spoils were
classified using the United States Department of Agriculture index by using a second subsample
of each spoil using ASTM D4318-10 (ASTM International, 2010).
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
To determine electrical conductivity, a modification of a U.S. Geological Survey (USGS)
field leach test was performed using a third subsample of each spoil (Hageman, 2007). The
modification involved the addition of 3% H2O2 to the sample in addition to distilled water (9:1
distilled water-to- H2O2 ratio) to promote the oxidation of minerals in the rocks and thus increase
the rate of dissolution (Skousen et al., 1997; Fallavena et al., 2012). Electrical conductivity of
the leachate was then determined using a multiparameter meter (HI991300; Hanna Instruments,
Woonsocket, RI).
Selenium concentrations were not measured since only sandstones not
adjacent (>2 m) to the coal seams were used. According to Vesper et al. (2008), sandstones
generally contain the lowest concentrations of Se with the exception of those adjacent to coal
beds. The authors found that Se concentrations were generally highest in sandstones within
0.5 m of the coal seam though in 10 samples, Se concentrations >2 mg L-1 were found more than
2 m from the coal seam. Vesper et al. (2008) noted that these higher Se concentration samples
were most often associated with a carbolith layer (e.g. either comprised of or immediately below
a high-Se carbolith layer). This trend was confirmed according to unpublished data collected by
R. Warner who in sampling two drill cores (33 m and 106 m) in West Virginia, found that the
lowest Se levels were associated with sandstones while the highest levels were found in the
shales, fire clays, and those sandstones adjacent to the coal seams.
Spoil Compaction and Permeability
To evaluate spoil compaction and permeability characteristics, a fourth subsample from each
spoil type was air dried and then ground (<2 mm) using a Thomas Wiley Laboratory Mill
Model 4 (Thomas Scientific, Swedesboro, NJ) in the Biosystems and Agricultural Engineering
Department. For each ground spoil sample, the Standard Proctor test (ASTM D698) was used to
determine the maximum achievable level of compaction (𝜌𝑚𝑎𝑥 ) for the optimum moisture
content (MC) (ASTM International, 2012). Moisture contents (gravimetric) ranged from 10 to
18% (IDT, 2013) and were assessed following the determination of 𝜌𝑚𝑎𝑥 . Because of this, not
all spoils were tested at the exact same MCs.
Following the Standard Proctor test (i.e.
determination of 𝜌𝑚𝑎𝑥 and MC values), a rigid wall double-ring permeameter, which was
constructed in the Biosystems and Agricultural Engineering Department, was used to determine
the saturated hydraulic conductivity (ℎ𝑠𝑎𝑡 ) of each spoil sample (Goldman et al., 1988).
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
Results and Discussion
Spoil Characterization
Table 2 contains the results of the USDA textural classification of the spoil samples.
Samples M1, M2, and M4, all of which contained brown sandstone, were classified as having a
loam texture while sample M3, which was gray sandstone, was classified as a sandy loam. All
spoil samples differed significantly from each other with respect to the percent of fines (silt and
clay) (p<0.001). Sample M1 had the largest percentage of fines at 62% followed by M4 at 53%,
M2 at 48%, and M3 at 27%. With the exception of M3, the percentage of fines in these samples
is higher than those measured by Agouridis et al. (2012) who found mean fines of 38% in the
brown sandstone samples and 24% in the gray sandstone samples. Miller et al. (2012) found
even lower percentages of fines in brown and gray sandstones at 22 and 21%, respectively. Note
that both Agouridis et al. (2012) and Miller et al. (2012) used the same procedure and laboratory
as used in this study. The results from this study coupled with those of Agouridis et al. (2012)
and Miller et al. (2012) show that the percentage of fines can vary considerably for the brown
and gray sandstones, but that the brown sandstones often have a greater percentage of fines than
the gray sandstones.
Table 3 contains the values for liquid limit, plastic limit, and plasticity index for the four
spoils. Both M1 and M4 were classified as ML according to the Universal Soil Classification
System (USCS) while M2 was close to this designation (ASTM International, 2006). M3 was
classified as an SM according to the USCS.
It is expected that a low permeability liner
constructed of these ML spoils would not experience significant shrinking and swelling as long
as they were not subjected to large changes in moisture contents (e.g. below 2 m or more of
spoil). As soils have very little tensile strength (Kim et al., 2012), they tend to crack when
subjected to differential settling, which can occur in valley fills. However, low permeability
liners have been successfully constructed in landfills using ML soils (R. Warner, personal
communication). The Pennsylvania Department of Environmental Protection (PDEP) (2011)
lists ML and SM soils as recommended types for use in dam embankment construction for oil
and gas wells.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
Table 2. Means and standard deviations of spoil texture values.
Texture
Spoil Sample1
M2
M3
M1
Percent Sand
A2
B
C
Mean ± Std. Dev.
Percent Silt
A
B
C
Mean ± Std. Dev.
Percent Clay
A
B
C
Mean ± Std. Dev.
USDA Textural Classification3
A
B
C
M4
40.5
37.2
37.4
38.4 ± 1.9
52.3
54.0
50.8
52.4 ± 1.6
73.5
72.9
72.4
72.9 ± 0.5
48.5
45.0
46.8
46.8 ± 1.7
41.7
39.5
45.4
42.2 ± 3.0
33.9
31.9
34.7
33.5 ± 1.5
16.5
17.2
17.4
17.0 ± 0.5
35.0
37.6
35.9
36.2 ± 1.3
17.8
23.4
17.3
19.5 ± 3.4
13.8
14.2
14.5
14.2 ± 0.3
10.1
9.9
10.2
10.1 ± 0.2
16.5
17.4
17.3
17.1 ± 0.5
loam
loam
loam
loam
sandy loam
loam
sandy loam
sandy loam
sandy loam
loam
loam
loam
1
M1 is100% brown sandstone, M2 is 100% brown sandstone, M3 is 100% gray sandstone, and M4 is 50% brown
sandstone and 50% gray sandstone.
2
A, B, and C refer to subsamples.
3
Source: USDA-NRCS (2012).
Table 3. Liquid limit, plastic limit, and plasticity index for each spoil sample.
Spoil Sample1
M1
M2
M3
M4
Liquid Limit (%)
31
25
17
27
Plastic Limit (%)
31
25
--2
24
Plasticity Index (%)
0
0
-3
1
M1 is100% brown sandstone, M2 is 100% brown sandstone, M3 is 100% gray sandstone, and M4 is 50% brown
sandstone and 50% gray sandstone.
2
Sample was too sandy to perform test.
Specific conductance values for all spoil samples were below 25 μS cm-1 except for the M2
spoil sample which was 46 μS cm-1 (Table 4). Miller et al. (2012) found average specific
conductivities of 80 and 90 μS cm-1 for brown and gray sandstones, respectively, at Bent
Mountain in Kentucky. Agouridis et al. (2012) measured higher specific conductance values for
brown (165 μS cm-1) and gray (147 μS cm-1) sandstones at the same mine as that in Miller et al.
(2012), using the same technique, but for different spoils. Emerson et al. (2009) measured
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
Table 4. Specific Conductance values for each spoil sample.
Specific Conductance (μS cm-1)
24
46
23
24
Spoil Sample1
M1
M2
M3
M4
1
M1 is100% brown sandstone, M2 is 100% brown sandstone, M3 is 100% gray sandstone, and M4 is 50% brown
sandstone and 50% gray sandstone.
specific conductance values between 270 and 440 μS cm-1 for brown sandstones and 240 to
250 μS cm-1 for gray sandstones in West Virginia. The higher specific conductance values
reported by Emerson et al. (2009) may be due to the methodology employed as the authors used
a 1:2 spoil:water mixture while Agouridis et al. (2012) and Miller et al. (2012) used a 1:3
spoil:water mixture. While the procedure for measuring specific conductance used in this study
was not identical to the methodology used by Emerson et al. (2009), Agouridis et al. (2012), and
Miller et al. (2012) and hence is not directly comparable, these studies show a trend that specific
conductance values for brown sandstones and gray sandstones are generally lower than
300 μS cm-1.While the purpose of the liner is to restrict the movement of water through
problematic spoils, and hence it could be argued that the quality (e.g. specific conductance) of
the spoil used to comprise the liner is of lesser importance, we recommend the use of higher
quality (e.g. low specific conductance, low Se producing) spoils. The reason is that water will
still flow along the upper boundary of the liner. If the liner is comprised of poorer quality spoils,
then the effectiveness of the liner at preventing water quality impairments will likely be reduced.
The spoils tested in this study were well below the 300-500 μS cm-1 threshold designated by the
USEPA. Though this one-time test was not sufficient to predict long-term mine drainage quality,
the low specific conductance levels measured for all the spoils were promising. Prior research
has shown that column tests have successfully predicted mine drainage quality (Bradham and
Carrucio, 1990; Stewart et al., 2001). Presently, a study is underway to compare the modified
USGS field leach or static test used in this paper to column testing (Daniels et al., 2013).
Considering only the specific conductance levels of the spoils from the static test, all samples
would be deemed acceptable for use in a low permeability barrier for isolating problematic
spoils. When compared to other specific conductance data presented in the literature, these
results point to the importance of testing individual strata rather than assuming a particular spoil
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
type, such as brown or gray sandstone, will produce low specific conductance values.
In
Agouridis et al. (2012), for example, it was noted that one test plot of brown weathered spoil
produced higher specific conductance values than the other.
Spoil Compaction and Permeability
Table 5 contains the maximum density and maximum saturated hydraulic conductivity values
for the tested spoils. Note that the extrapolated values were used in some cases; however, this
does not affect the interpretation of the results as the order of magnitude, which is of primary
interest, does not change. Maximum density was highest for M3 and M4 at about 2,500 kg m -3
followed by M2 at 2,400 kg m-3, and M1 at 2,200 kg m-3. Samples M3 and M4 both contained
gray sandstone at 100% and 50%, respectively. As seen in Fig. 2-5 and Table 5, the moisture
contents required to reach these maximum densities were between about 12 and 14% for all
samples except M1 which required a moisture content of about 17%.
Table 5. Maximum density and saturated hydraulic conductivity values for the sampled spoils.
1
Spoil Sample1
𝜌𝑚𝑎𝑥 (kg m-3)
M1
M2
M3
M4
2,200
2,400
2,500
2,500
Moisture Content
(%)
17
14
12
13
ℎ𝑠𝑎𝑡 (cm s-1)
6x10-8
1x10-7
3x10-7
3x10-7
Moisture Content
(%)
17
14
11
13
M1 is100% brown sandstone, M2 is 100% brown sandstone, M3 is 100% gray sandstone, and M4 is 50% brown
sandstone and 50% gray sandstone.
Figures 2-5 and Table 5 show that the saturated hydraulic conductivity was highest for M3
followed by M4, M2, and M1 (note that lower saturated hydraulic conductivity values are
desired for liners or barriers). With the exception of M1, these saturated hydraulic conductivity
values were above the maximum level (1 x 10-7 cm s-1) required for soil (e.g. clay) liners used in
waste management facilities as outlined in Part 258, Subpart D of the Code of Federal
Regulations (Goldman et al., 1988). Sample M2 was relatively close to the 1 x 10-7 cm s-1 level.
Thus, M1 and M2, which contained 100% brown sandstone, had the lowest saturated hydraulic
conductivities. Sample M3 and M4, which contained gray sandstone, had slightly higher values
for saturated hydraulic conductivities. These results suggest that brown sandstone may be a
more suitable media for constructing a low permeability barrier than gray sandstone.
Additionally, Miller et al. (2012) found that brown weathered sandstone was less durable than
gray unweathered sandstone suggesting that, in the field, it will be easier to crush the brown
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
weathered sandstone with a dozer or other such mine equipment. Part of the reason may be
related to the percentage of fines in the samples (Fig. 6). As the percentage of fines increased,
saturated hydraulic conductivity tended to decrease. Goldman et al. (1988) showed that the
percent fines in clay liners is typically 50% or greater. With the exception of M3, which was the
one sample containing only gray sandstone, the other samples met or nearly met this criterion.
At this time, it is important to note that no maximum saturated hydraulic conductivity guideline
has been established for low permeability barriers used to isolate problematic spoils. It is
possible that a maximum saturated hydraulic conductivity value higher than the one required for
waste management facilities (e.g. greater than 1 x 10-7 cm s-1) would prevent or limit the leaching
of constituents from problematic spoils.
2250
1.2x10-6
-3
Density (kg m )
10-6
2200
8.0x10-7
2150
6.0x10-7
2100
4.0x10-7
2050
2000
10
2.0x10-7
12
14
16
18
-1
Density
Saturated Hydraulic Conductivity
Saturated hydraulic conductivity (cm s )
1.4x10-6
2300
20
Moisture Content (%)
Figure 2. Maximum density and saturated hydraulic conductivity results for sample M1 (100%
brown sandstone). Dashed vertical line represents the minimum saturated hydraulic
conductivity.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
-1
Density
Saturated Hydraulic Conductivity
2380
8x10-7
-3
Density (kg m )
2360
2340
6x10-7
2320
2300
4x10-7
2280
2260
2x10-7
2240
2220
10
12
14
16
18
Saturated Hydraulic Conductivity (cm s )
10-6
2400
20
Moisture Content (%)
Figure 3. Maximum density and saturated hydraulic conductivity results for sample M2 (100%
brown sandstone). Dashed vertical line represents the minimum saturated hydraulic
conductivity.
-3
Density (kg m )
-1
Density
Saturated Hydraulic Conductivity
2480
2.5x10-6
2460
2.0x10-6
2440
1.5x10-6
2420
10-6
2400
5.0x10-7
2380
10
12
14
16
18
Saturated Hydraulic Conductivity (cm s )
3.0x10-6
2500
20
Moisture Content (%)
Figure 4. Maximum density and saturated hydraulic conductivity results for sample M3 (100%
gray sandstone). Dashed vertical line represents the minimum saturated hydraulic
conductivity.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
-3
Density
Saturated Hydraulic Conductivity
5.0x10-7
2440
4.5x10-7
-3
Density (kg m )
Saturated Hydraulic Conductivity (g cm )
5.5x10-7
2460
2420
4.0x10-7
2400
3.5x10-7
2380
3.0x10-7
2.5x10-7
2360
10
12
14
16
18
20
Moisture Content (%)
Figure 5. Maximum density and saturated hydraulic conductivity results for sample M4 (50%
brown sandstone and 50% gray sandstone). Dashed vertical line represents the
minimum saturated hydraulic conductivity.
R2=0.55
-1
Saturated Hydraulic Conductivity (cm s )
3.5e-7
3.0e-7
2.5e-7
2.0e-7
1.5e-7
1.0e-7
5.0e-8
0.0
30
40
50
60
Fines (%)
Figure 6. Saturated hydraulic conductivity versus the percentage of fines (silt and clay) in the
spoil sample.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
In all cases, the maximum saturated hydraulic conductivity occurred at a moisture content at
or nearly at proctor (i.e. maximum density). This moisture content finding is in the lower range
of those presented by Goldman et al. (1988). For the lowest saturated hydraulic conductivity, the
authors reported moisture content values that were typically 2% above the moisture content
required for proctor.
Conclusions
Isolating high specific conductance and Se producing spoils using a low permeability barrier
(i.e. source reduction) is one possible method to help mitigate the impacts of mining operations
on headwater streams. Such barriers or liners are commonly employed in landfills and in active
coal mining operations where acid-forming strata are encountered. However, landfill liners are
constructed of clay which is a material of limited quantities in the Appalachian coalfields.
Furthermore, the shales and fire clays found in this region are often unacceptable due to elevated
specific conductance and/or Se levels as these shales and clays are found adjacent to the coal
seams. Sandstones on the other hand are abundant in the Appalachian coalfields and typically
have low specific conductance and Se levels.
The results of this laboratory study demonstrate that brown sandstones are a promising
material for use in construction of a low permeability barrier to isolate problematic spoils
provided that the sandstones used have low levels of specific conductance and leachable Se. The
two brown sandstone spoils tested met or exceeded the recommended saturated hydraulic
conductivity threshold of 1 x 10-7 cm s-1 for waste management facilities while the samples
containing gray sandstone had higher values (e.g. were more permeable). As noted by Olson and
Daniel (1981), saturated hydraulic conductivity values recorded in the laboratory are almost
always lower than those recorded in the field. This difference is due to factors such as the
screening of laboratory samples to remove gravels, roots, and other large items; the use of
different compaction devices in the laboratory and the field; the presence of macro-pores, cracks
or other preferential flow paths in larger field samples (Daniel, 1984; Stewart and T.W. Nolan
1987); and the challenges associated with achieving the optimal moisture content in the field. As
such, it is expected that the achievable field saturated hydraulic conductivity values for the spoils
examined in this study will be higher than the laboratory values measured. However, this does
not mean that a low permeability barrier with saturated hydraulic conductivity value > 1 x 10-
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 1
7
cm s-1 is not acceptable when isolating problematic spoils. A higher value may provide the
needed water quality protection.
Acknowledgements
The authors would like to thank Alex Fogle and Lloyd Dunn for their invaluable assistance in
conducting this study. The authors would also like to thank the anonymous reviewers for their
comments. This study was sponsored by the Appalachian Research Initiative for Environmental
Science (ARIES). The views, opinions and recommendations expressed herein are solely those
of the authors and do not imply any endorsement by ARIES employees, other ARIES-affiliated
researchers, or industrial members.
Information about ARIES can be found at
http://www.energy.vt.edu/ARIES .
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