6 research outputs found
Environmental Impacts of the Tennessee Valley Authority Kingston Coal Ash Spill. 2. Effect of Coal Ash on Methylmercury in Historically Contaminated River Sediments
The Tennessee Valley Authority Kingston coal ash spill
in December
2008 deposited approximately 4.1 million m<sup>3</sup> of fly ash
and bottom ash into the Emory and Clinch River system (Harriman, Tennessee,
U.S.A.). The objective of this study was to investigate the impact
of the ash on surface water and sediment quality over an eighteen
month period after the spill, with a specific focus on mercury and
methylmercury in sediments. Our results indicated that surface water
quality was not impaired with respect to total mercury concentrations.
However, in the sediments of the Emory River near the coal ash spill,
total mercury concentrations were 3- to 4-times greater than sediments
several miles upstream of the ash spill. Similarly, methylmercury
content in the Emory and Clinch River sediments near the ash spill
were slightly elevated (up to a factor of 3) at certain locations
compared to upstream sediments. Up to 2% of the total mercury in sediments
containing coal ash was present as methylmercury. Mercury isotope
composition and sediment geochemical data suggested that elevated
methylmercury concentrations occurred in regions where native sediments
were mixed with coal ash (e.g., less than 28% as coal ash in the Emory
River). This coal ash may have provided substrates (such as sulfate)
that stimulated biomethylation of mercury. The production of methylmercury
in these areas is a concern because this neurotoxic organomercury
compound can be highly bioaccumulative. Future risk assessments of
coal ash spills should consider not only the leaching potential of
mercury from the wastes but also the potential for methylmercury production
in receiving waters
Environmental Impacts of the Tennessee Valley Authority Kingston Coal Ash Spill. 1. Source Apportionment Using Mercury Stable Isotopes
Mercury stable isotope abundances were used to trace
transport
of Hg-impacted river sediment near a coal ash spill at Harriman, Tennessee,
USA. δ<sup>202</sup>Hg values for Kingston coal ash released
into the Emory River in 2008 are significantly negative (−1.78
± 0.35‰), whereas sediments of the Clinch River, into
which the Emory River flows, are contaminated by an additional Hg
source (potentially from the Y-12 complex near Oak Ridge, Tennessee)
with near-zero values (−0.23 ± 0.16‰). Nominally
uncontaminated Emory River sediments (12 miles upstream from the Emory-Clinch
confluence) have intermediate values (−1.17 ± 0.13‰)
and contain lower Hg concentrations. Emory River mile 10 sediments,
possibly impacted by an old paper mill has δ<sup>202</sup>Hg
values of −0.47 ± 0.04‰. A mixing model, using
δ<sup>202</sup>Hg values and Hg concentrations, yielded estimates
of the relative contributions of coal ash, Clinch River, and Emory
River sediments for a suite of 71 sediment samples taken over a 30
month time period from 13 locations. Emory River samples, with two
exceptions, are unaffected by Clinch River sediment, despite occasional
upstream flow from the Clinch River. As expected, Clinch River sediment
below its confluence with the Emory River are affected by Kingston
coal ash; however, the relative contribution of the coal ash varies
among sampling sites
Selenium Speciation in Coal Ash Spilled at the Tennessee Valley Authority Kingston Site
Selenium (Se) in
coal ash spills poses a threat to adjacent ecosystems
because of its potential to mobilize and bioaccumulate in aquatic
organisms. Given that the mobility and bioavailability of Se is controlled
by its valence states, we aimed to define Se speciation in coal ash
solids and examine the relationships between Se speciation and the
magnitude of its mobilization from coal ash. We used coal ash samples
from the Tennessee Valley Authority (TVA)-Kingston fossil plant and
the site of a coal ash spill that occurred in 2008 in Tennessee. Results
of X-ray absorption spectroscopic analyses showed that Se in coal
ash samples was a mixture of elemental Se<sup>0</sup> and Se oxyanions.
The amount of leachable Se increased with an increase of pH from 3
to 13. At the natural pH of coal ash samples (from pH 7.6 to 9.5),
the leachable Se was comprised of Se oxyanions, mainly selenite. This
was observed by both direct quantification of Se oxyanions in the
leachate and the corresponding loss of Se oxyanions in the solid phase.
At pH 12, however, the Se release appeared to derive from both desorption
of Se oxyanions and oxidative dissolution of elemental Se<sup>0</sup>. Our results indicate that Se oxyanions are the most labile species;
however, the magnitude of Se mobilization will increase if the waste
material is subjected to alkaline conditions
The Impact of Coal Combustion Residue Effluent on Water Resources: A North Carolina Example
The combustion of coal to generate electricity produces
about 130
million tons of coal combustion residues (CCRs) each year in the United
States; yet their environmental implications are not well constrained.
This study systematically documents the quality of effluents discharged
from CCR settling ponds or cooling water at ten sites and the impact
on associated waterways in North Carolina, compared to a reference
lake. We measured the concentrations of major and trace elements in
over 300 samples from CCR effluents, surface water from lakes and
rivers at different downstream and upstream points, and pore water
extracted from lake sediments. The data show that CCR effluents contain
high levels of contaminants that in several cases exceed the U.S.
EPA guidelines for drinking water and ecological effects. This investigation
demonstrates the quality of receiving waters in North Carolina depends
on (1) the ratio between effluent flux and freshwater resource volumes
and (2) recycling of trace elements through adsorption on suspended
particles and release to deep surface water or pore water in bottom
sediments during periods of thermal water stratification and anoxic
conditions. The impact of CCRs is long-term, which influences contaminant
accumulation and the health of aquatic life in water associated with
coal-fired power plants
Isotopic Imprints of Mountaintop Mining Contaminants
Mountaintop
mining (MTM) is the primary procedure for surface coal
exploration within the central Appalachian region of the eastern United
States, and it is known to contaminate streams in local watersheds.
In this study, we measured the chemical and isotopic compositions
of water samples from MTM-impacted tributaries and streams in the
Mud River watershed in West Virginia. We systematically document the
isotopic compositions of three major constituents: sulfur isotopes
in sulfate (δ<sup>34</sup>S<sub>SO4</sub>), carbon isotopes
in dissolved inorganic carbon (δ<sup>13</sup>C<sub>DIC</sub>), and strontium isotopes (<sup>87</sup>Sr/<sup>86</sup>Sr). The
data show that δ<sup>34</sup>S<sub>SO4</sub>, δ<sup>13</sup>C<sub>DIC</sub>, Sr/Ca, and <sup>87</sup>Sr/<sup>86</sup>Sr measured
in saline- and selenium-rich MTM impacted tributaries are distinguishable
from those of the surface water upstream of mining impacts. These
tracers can therefore be used to delineate and quantify the impact
of MTM in watersheds. High Sr/Ca and low <sup>87</sup>Sr/<sup>86</sup>Sr characterize tributaries that originated from active MTM areas,
while tributaries from reclaimed MTM areas had low Sr/Ca and high <sup>87</sup>Sr/<sup>86</sup>Sr. Leaching experiments of rocks from the
watershed show that pyrite oxidation and carbonate dissolution control
the solute chemistry with distinct <sup>87</sup>Sr/<sup>86</sup>Sr
ratios characterizing different rock sources. We propose that MTM
operations that access the deeper Kanawha Formation generate residual
mined rocks in valley fills from which effluents with distinctive <sup>87</sup>Sr/<sup>86</sup>Sr and Sr/Ca imprints affect the quality
of the Appalachian watersheds
Isotopic Imprints of Mountaintop Mining Contaminants
Mountaintop
mining (MTM) is the primary procedure for surface coal
exploration within the central Appalachian region of the eastern United
States, and it is known to contaminate streams in local watersheds.
In this study, we measured the chemical and isotopic compositions
of water samples from MTM-impacted tributaries and streams in the
Mud River watershed in West Virginia. We systematically document the
isotopic compositions of three major constituents: sulfur isotopes
in sulfate (δ<sup>34</sup>S<sub>SO4</sub>), carbon isotopes
in dissolved inorganic carbon (δ<sup>13</sup>C<sub>DIC</sub>), and strontium isotopes (<sup>87</sup>Sr/<sup>86</sup>Sr). The
data show that δ<sup>34</sup>S<sub>SO4</sub>, δ<sup>13</sup>C<sub>DIC</sub>, Sr/Ca, and <sup>87</sup>Sr/<sup>86</sup>Sr measured
in saline- and selenium-rich MTM impacted tributaries are distinguishable
from those of the surface water upstream of mining impacts. These
tracers can therefore be used to delineate and quantify the impact
of MTM in watersheds. High Sr/Ca and low <sup>87</sup>Sr/<sup>86</sup>Sr characterize tributaries that originated from active MTM areas,
while tributaries from reclaimed MTM areas had low Sr/Ca and high <sup>87</sup>Sr/<sup>86</sup>Sr. Leaching experiments of rocks from the
watershed show that pyrite oxidation and carbonate dissolution control
the solute chemistry with distinct <sup>87</sup>Sr/<sup>86</sup>Sr
ratios characterizing different rock sources. We propose that MTM
operations that access the deeper Kanawha Formation generate residual
mined rocks in valley fills from which effluents with distinctive <sup>87</sup>Sr/<sup>86</sup>Sr and Sr/Ca imprints affect the quality
of the Appalachian watersheds