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 m³ 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. δ²⁰²Hg 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 δ²⁰²Hg values of −0.47 ± 0.04‰. A mixing model, using δ²⁰²Hg 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 Se⁰ 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 Se⁰. 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 (δ³⁴S_SO4), carbon isotopes in dissolved inorganic carbon (δ¹³C_DIC), and strontium isotopes (⁸⁷Sr/⁸⁶Sr). The data show that δ³⁴S_SO4, δ¹³C_DIC, Sr/Ca, and ⁸⁷Sr/⁸⁶Sr 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 ⁸⁷Sr/⁸⁶Sr characterize tributaries that originated from active MTM areas, while tributaries from reclaimed MTM areas had low Sr/Ca and high ⁸⁷Sr/⁸⁶Sr. Leaching experiments of rocks from the watershed show that pyrite oxidation and carbonate dissolution control the solute chemistry with distinct ⁸⁷Sr/⁸⁶Sr 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 ⁸⁷Sr/⁸⁶Sr 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 (δ³⁴S_SO4), carbon isotopes in dissolved inorganic carbon (δ¹³C_DIC), and strontium isotopes (⁸⁷Sr/⁸⁶Sr). The data show that δ³⁴S_SO4, δ¹³C_DIC, Sr/Ca, and ⁸⁷Sr/⁸⁶Sr 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 ⁸⁷Sr/⁸⁶Sr characterize tributaries that originated from active MTM areas, while tributaries from reclaimed MTM areas had low Sr/Ca and high ⁸⁷Sr/⁸⁶Sr. Leaching experiments of rocks from the watershed show that pyrite oxidation and carbonate dissolution control the solute chemistry with distinct ⁸⁷Sr/⁸⁶Sr 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 ⁸⁷Sr/⁸⁶Sr and Sr/Ca imprints affect the quality of the Appalachian watersheds