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Critique Paper
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Samuel Janes
The self-ignition of exposed and underground coal seams that results in “coal fires” has
caused significant ecological, economic, and personal causalities in the United States and
globally in recent years (Hetao et al. 2016). These fires cause coal that is mined as a
nonrenewable energy source to become unusable, as well as contributing large quantities of
atmospheric pollution, vegetation loss, and ecological stress on soil and water systems (Lu et al.
2015). Climate change organizations have also recognized that the collective spontaneous
combustion of coal across the globe poses as a significant source for greenhouse gas emissions
(Pone et al. 2007). There have been recent efforts in the development of research that aims to
identify sources of mine fires, prevention techniques for spontaneous combustion, and control
measures (Cui et al. 2015; Lu et al. 2015). This critique analyzes the volatile organic compounds
and mine-derived chemical compounds found in soil and water surrounding two coal fires in
eastern Kentucky (Garrison et al. 2016).
Lu et al. (2015) defines coal fires as those that “occur most frequently in exposed or
underground coal seams featured with large area, high temperature, and long duration” (18383).
Frequent locations of coal fires include “abandoned coal mines, unmined outcrops, waste banks,
and coal stockpiles” (Shao et al. 2017, 1313). The ratio of oxygen concentration within a mine is
a key factor for self-ignition, where concentrations between 10-18 percent have shown most to
be most at risk, causing high levels of oxidation to minerals and increasing heat production
(Hetao et al. 2016). Temperatures can increase to over 800℃ and ignition can sustain for several
decades (Shao et al. 2017). In China alone, betwen100-200 Megatons (Mt) of coal are consumed
yearly by spontaneous absorption alone (Baris and Dedari 2009; Cui et al. 2015).
Within this self-combustion coal, there are several chemical constituents being emitted
that are of particular interest when sourcing greenhouse gases, chiefly carbon dioxide (CO2) and
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carbon monoxide (CO) (Garrison et al. 2016). Other coal-fire emissions that are potentially
harmful include C1-C10 hydrocarbons, benzene, toluene, ethylbenzene, and xylene isomers
(BTEX), as well as polynuclear aromatic hydrocarbons (PAH’s). BTEX compounds have been
shown to be carcinogenic, while PAH’s are carcinogenic, mutagenic, and teratogenic in nature
(Garrison et al. 2016). Coal fires, such as the Truman Shepherd, Lotts Creek, and surrounding
fires in the Appalachian Basin of eastern Kentucky, often have residential homes facing the
ridges that contain the fires, which point to potential health risks from emissions that settle in the
mountainous valleys through temperature inversions (Garrison et al. 2016; Hower et al. 2013).
The study conducted by Garrison et al. (2016) collected samples from two coal fires
occurring in Knott and Perry County, Kentucky. The first is the Truman Shepherd fire, which is
found in a mountainous valley around 10 meters from the neighboring Rock Fork Creek, and 50
meters from Howard Branch. The soil type at this location is prevalent in siltstones, shales, and
sandstones, and from hydrogeological connectivity sampling from the Howard Branch Well that
intersects the coal seam, groundwater moving through the porosity of these soils would take
longer than a week to reach the well. This time lapse shows that ground water is likely
transported through preexisting fractures from the coal mine. The second site is the Lotts Creek
fire, which is positioned near a forested mountaintop, and features steep slopes, rocky soils, and
several ridges. Unlike at the Truman Shepherd fire, this site contains a small organic layer in the
soil, with a sandy loam present beneath the humic matter from the sandstone-predominant parent
material. This site did not have a significant amount of groundwater or surface water because of
the higher elevation (~350meters above sea level). Overall, the authors infer that the porosity and
hydraulic conductivity of these mountainous soils in eastern Kentucky is low because of
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cementation of sandstone in subsoil layers. Fracturing of soils and parent material from coal
mines could is likely to increase those conductivity levels.
In their methodology, water samples for both groundwater and surface water were taken
at the Truman Shepherd site from the Howard well, the adjoining Bentley well, and at Rock Fork
Creek, both near the fire as well as down gradient of the coal seam. There were no pre-fire
samples that could be retrieved, so the researchers took a water sample upstream of the fire and
at a background well. For soil samples, nine specimens were retrieved at the mined site, and a
control sample was taken 100 meters east of the coal seam. For the Lotts Creek site, since there
was limited water available for sampling, one simple was retrieved from a ditch approximately
10 meters below the coal fire. For soil sampling, 18 specimens were collected around various
coal fire vents surrounding the seam, and when multiple samples at one vent were taken, they
were spaced around 1 meter apart. Analyses for BTEX, PAH’s, cyanide, and total organic carbon
were taken for each of the soil and water samples (Garrison et al. 2016).
At the Truman Shepherd (TS) site, the results from the water analyses showed that there
was only one detection of BTEX, PAH’s, or cyanide present (i.e. ethylbenzene at 0.00064mg/L).
However, there were several soil samples that showed a detectable BTEX compound (xylene
isomer in 6 of 9 samples, 0.0005-0.002 mg/kg). There were also PAH’s (naphthalene and
phenanthrene) detected in 7 seven of the soil samples, where naphthalene concentration’s range
(0.059-0.065mg/kg) exceeded the EPA Soil Screening Level (SSL) of 0.00054mg/kg. The total
organic carbon (TOC) concentrations for this site’s soils ranged from 3.18-4.06% C, and cyanide
concentrations were all below the detection limit (Garrison et al. 2016).
For the Lotts Creek (TC) site data analyses, there was no observable contamination in
any of the water samples. However, there was a distinct difference in the soil sample analyses
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compared to the Truman Shepherd site. Each BTEX compound (i.e. benzene, toluene, ethyl
benzene, xylene, and cyanide) that was studied was found in multiple samples, several of which
were above EPA’s SSL. In addition, the background (BG) sample also contained all BTEX
compounds, where Garrison et al. (2016) suggests that this indicates “atmospheric transport of
volatile contaminants” (574). Xylene concentrations were a magnitude greater at LC
(0.038mg/kg) than TS (0.0005-0.002mg/kg). Each of the PAH compounds studied (naphthalene,
acenaphthylene, acenaphthene, fluorine, anthracene, phenanthrene, pyrene, and fluoranthene)
was found at detectable levels in at least one sample, and all samples with the exception to the
BG contained multiple PAH’s. This site also displayed increased percentages of TOC (3.1814.32% C) compared to the TS site (3.18-4.06% C), and the cyanide concentrations found at
detectable levels at LC were higher than the EPA SSL (Garrison et al. 2016).
The conclusions from the discussion of their data showed that BTEX and PAH
compounds were essentially nonexistent in water samples for both sites, and is inferred that the
scope of these types of contaminations decreases significantly with distance from coal seam
vents. Their data did show that BTEX and PAH’s were more common to persist in soils rather
than water, and greater concentrations of PAH’s are present compared to BTEX compounds.
Garrison et al. (2016) gather that this relationship is due to the “preferential partitioning
(sorption) to soil organic matter, which increases with atomic mass and the complexity of
molecular structure” (574). They suggest that the increased BTEX and PAH contamination at
Lotts Creek could be stemmed from the increased TOC levels and the higher sorption capacity it
expresses compared to soils at Truman Shepherd.
The authors stated at the beginning of their project review that there is no scientific
literature present in the field of environmental chemistry dealing specifically with groundwater
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and soil effects from coal mine fires (Garrison et al. 2016). In order for their study to contain
proxies to use as comparison in their data collection, they had to use experimental data from
underground coal gasification (UCG) projects that focused on contamination. The UCG projects
that are presently being used to compare potential impacts coal fires have on soil contamination
have suggested that there is a link in the contaminant transport from coal seam mines and the
relative persistence the contaminants have within surrounding soils (Pandey et al. 2016).
A study conducted by Pandey et al. (2016) showed that the highest deposition of trace
elements (Cd, Zn, Pb) from mining in the soil were found closest to the mine itself, and that coal
fires contributed 46% to the soil pollution at their site. Another study led by Kapusta and
Stańczyk (2015) showed similar results result via UCG, where the PAH’s, along with metal ions
Zn and Se, were more concentrated in hard coal condensate samples, which correlated to high
levels of acute toxicity that could translate to the sorption into connecting soils and parent
material. A separate study completed by Shuqin et al. (2004) found that the leaching of trace
elements from a lignite residue in an UCG is influenced heavily by the pH of the leaching
solution and the physical form the elements exist in. This could be an interesting link for future
studies when focusing on soil effects from coal seam fires, where data could be gathered to find
the relationship soil pH might have on the ease at which trace elements and compounds such as
PAH’s leach and adsorb onto soil particles.
Another interesting aspect to researchers’ efforts in managing the quality of mining water
resources involves the potential pollution control measures for limiting groundwater
contamination. Verma et al. (2014) agree with the hypotheses and conclusions from Garrison et
al. (2016) that concentration of mining compounds like BTEX and PAH’s decrease as the
distance from the mine cavity increases, but their mitigation suggestions raises some concerns.
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For example, they propose pumping contaminated water out for surface dispersal in order to
remove highly mobile contaminants, but this strategy does not consider the potential TOC
percentages found in the soils where contaminated water will be pumped. Based on Garrison’s
findings, this approach could pose as problematic by increases the concentration of BTEX and
PAH compounds that tend to adsorb to soils with high TOC levels. This is a new observation that
could be added to systematic approaches of future studies similar to Garrison et al. (2016) that
aims to connect the identification of coal seam fire effects on soil quality with the most effective
mitigation strategies to mend the contamination and degradation of ecosystems.
There have been multiple studies conducted that consider potential approaches for
extinguishing large-scale coal fires as a means to limit emissions and contamination threats. Lu
et al. (2015) proposes the use of gas-liquid foaming agents that are inserted into blast drilling
holes via jet cavitation, which has shown to be superior at extinguishing fires. Relative
temperatures inside coal seams are 6-7 magnitudes higher when using water infusion as the
means to extinguish fires compared to foaming agents, and concentrations of CO have been
shown to decrease from rates of 9.43 to 0.092% after foams are infused. In fact, chemists have
shown that managing the levels of water-inrush are conducive to regulating the amount of
temperature increasing within a coal seam (Yang et al. 2008). If studies can continue to confirm
gas-liquid foaming agents’ effectiveness, this could become a mitigation approach that would
lessen the amount of emissions contaminations that occur from coal seam fires.
Another study published reviews the soil amelioration effects that can occur through the
use of solid fly ash (FA) waste from coal-fired power plants (Ram and Masto 2014). FA has been
found to contain several favorable soil amendment qualities, such as silt-sized particles, an
advantageous pH value, and beneficial nutrients for plant growth and biomass production, some
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of which could be applied to the effects BTEX and PAH contaminants have on mine soils. While
there are slight risks that the addition of FA to mine soils could add additional trace elements and
soluble salts into soil-plant-human systems, the risks are minimized when very weathered FA is
used rather than fresh quantities from coal plants.
A specific property of coal fires that is important for researchers and practitioners to be
mindful of when developing experimental projects or mitigation techniques is the relative
thickness of the coal seam layer. A study conducted by Yang (2008) found that when coal seam
layers are less than 2meters in thickness, a considerable cooling action of the surrounding rocks
in the mine affects the heat intensity of coal gas. Practitioners also suggest that raising the
intensity of oxygen-enhanced air that is blown into thin coal seam layers can aid in the heating
value of coal gas that continues to self ignite. Regulating the amount of air circulation in a coal
seam fire relative to its seam thickness could be a strategic mitigation technique in reducing
emission rates and continued threats of soil and water contamination.
Another alternative amelioration technique that practitioners are implementing to
extinguish coal fires involves drilling holes in the ground at the affected site in a parallel
direction to the spreading fire. Holes were organized consistently along an axis around the fire
area, and then were sealed with grouting, which is type of mortar paste used to fill and cement
crevices or openings in the ground. Extra holes are then drilled to prevent crystalline deposition
of gaseous coal fire products (i.e. epitaxy), and airtightness of the drilled holes was ensured to
prevent gasification of adjoining mines (Cui et al. 2015). While this method is known to save
money in extinguishing techniques and improving firefighting proficiency, there are several
structural and ecological risks that could cause even more severe problems with coal seam fires,
such as collapse of the open mine pit due to drilling, inefficient sealing of holes and influx of
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water and/or release of emission gases, all of which could contribute to the increase self-ignition
rates. Future studies could be conducted that aim to collect meta analysis data on the relative
success of coal fire drillings for extinguishment compared to other mitigation strategies, such as
gas-liquid foaming agents and the rates of oxygen-rich air circulation in the mine.
While there are some links between this study and the results shown in several UCG
projects, the observations and findings are unique and significant relative to other environmental
chemistry literature present for coal seam fire effects. The novelty in this research could be a
“first step in understanding soil and water quality near coal fires” (Garrison et al. 2016, 574).
Future studies could be conducted at coal seam fires prevalent across the country that aim to
determine the chemical relationship between TOC levels in soils and the relative levels of BTEX
and PAH compounds from fire emissions. Another notable component of future coal fire
research on soil quality that would be important to determine is the effect soil moisture levels
have on the accumulation of BTEX and PAH compounds. Studies have indicated that these
compounds can accumulate in wet and dry soil conditions (Cachada et al. 2012). This could lead
to assessing regional soil quality and climatic trends, where certain moisture regimes would be
more likely to accumulate coal fire contaminants if there are correlations. There are several
challenges facing studies of this type, including the availability of sites with adequate water for
sampling that is hydogeologically connected to the coal fire, especially in mountainous areas like
Eastern Kentucky and Pennsylvania, and challenging arid locations like New Mexico and
Southern Texas (Garrison et al. 2016). Studies could also elaborate more in depth on the
chemical properties expressed for sorption capacity that coal fire emission compounds express
when there are organic materials in soils surrounding a coal mine.
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