Louis M. McDonald

Review of Passive Systems for Acid Mine Drainage Treatment

When appropriately designed and maintained, passive systems can provide long-term, efficient, and effective treatment for many acid mine drainage (AMD) sources. Passive AMD treatment relies on natural processes to neutralize acidity and to oxidize or reduce and precipitate metal contaminants. Passive treatment is most suitable for small to moderate AMD discharges of appropriate chemistry, but periodic inspection and maintenance plus eventual renovation are generally required. Passive treatment technologies can be separated into biological and geochemical types. Biological passive treatment technologies generally rely on bacterial activity, and may use organic matter to stimulate microbial sulfate reduction and to adsorb contaminants; constructed wetlands, vertical flow wetlands, and bioreactors are all examples. Geochemical systems place alkalinity-generating materials such as limestone in contact with AMD (direct treatment) or with fresh water up-gradient of the AMD. Most passive treatment systems employ multiple methods, often in series, to promote acid neutralization and oxidation and precipitation of the resulting metal flocs. Before selecting an appropriate treatment technology, the AMD conditions and chemistry must be characterized. Flow, acidity and alkalinity, metal, and dissolved oxygen concentrations are critical parameters. This paper reviews the current state of passive system technology development, provides results for various system types, and provides guidance for sizing and effective operation.ZusammenfassungPassive Systeme können über einen langen Zeitraum unterschiedlichste saure Grubenwässer (AMD) effizient und wirksam reinigen, sofern sie sachgerecht geplant und errichtet werden. Die passive Reinigung saurer Grubenwässer beruht auf natürlichen Prozessen der Säureneutralisation, Oxidation oder Reduktion und Ausfällung von metallischen Schadstoffen. Die Anwendung passiver Reinigungssysteme ist besonders geeignet für kleine bis mittlere AMD-Ströme mit entsprechendem Chemismus. Die periodische Überprüfung und Instandhaltung und gegebenfalls Erneuerung sind aber generell notwendig. Die passiven Reinigungstechnologien können in biologische und geochemische Typen eingeteilt werden. Die biologische Reinigung beruht generell auf bakterieller Tätigkeit und kann organisches Material nutzen um beispielsweise die mikrobielle Sulfatreduktion anzuregen und Verunreinigungen zu adsorbieren. Beispiele für biologische Systeme sind Pflanzenkläranlagen, vertikal durchströmte Pflanzenkläranlagen und Bioreaktoren. Geochemische Systeme bringen alkalisch wirkende Stoffe, wie z. B. Kalkstein, in Kontakt mit sauren Grubenwässern (direkte Reinigung) oder mit dem Frischwasseranstrom von sauren Grubenwässern. Die meisten passiven Reinigungssysteme verwenden multiple Methoden, um die Säureneutralisation, Oxidation und Ausfällung von Metallen zu fördern. Bevor ein geeignetes Reinigungssystem gewählt wird, müssen die AMD-Bedingungen sowie der Chemismus charakterisiert werden. Wesentliche Parameter sind der Durchfluss, die Acidität und Alkalinität sowie die Konzentration von Metallen und Sauerstoff. Der vorliegende Artikel bewertet den aktuellen Stand der Entwicklung passiver Systeme, stellt Ergebnisse verschiedener Systemtypen vor und bietet Hilfestellung bei der Dimensionierung und einem erfolgreichen Einsatz solcher Systeme.ResumenLos sistemas pasivos, apropiadamente diseñados y mantenidos, pueden proporcionar un efectivo y eficiente tratamiento, y por largo tiempo, de muchos drenajes ácidos de minas (AMD). Los tratamientos pasivos utilizan procesos naturales para neutralizar la acidez y oxidar o reducir y precipitar los metales contaminantes. Los tratamientos pasivos son más adecuados para pequeñas y moderadas descargas de AMD de química apropiada, pero se requieren generalmente periódicas inspecciones y periódico mantenimiento, más eventuales renovaciones. Las tecnologías pasivas de tratamiento pueden ser separadas entre biológicas y geoquímicas. Las biológicas utilizan la actividad bacteriana y pueden adicionar material orgánico para estimular la reducción microbiana de sulfato y para adsorber los contaminantes; ejemplos estas tecnologías son los humedales artificiales, los humedales de flujo vertical y los biorreactores. Los sistemas geoquímicos utilizan materiales generadores de alcalinidad como la caliza en contacto con AMD (tratamiento directo) o con agua fresca gradiente arriba del AMD. La mayoría de los sistemas de tratamiento pasivo emplean múltiples métodos, frecuentemente en serie, para lograr la neutralización de ácidos y la precipitación de los metales. Antes de seleccionar la tecnología de tratamiento apropiada, se deben caracterizar las condiciones del AMD. Los parámetros críticos son flujo, acidez y alcalinidad y concentraciones de oxígeno disuelto y metales. Este trabajo revisa el actual desarrollo de la tecnología de sistemas pasivos, muestra resultados obtenidos en varios tipos de sistemas y proporciona una guía orientativa sobre el tamaño necesario para una operación efectiva.酸性废水被动处理系统综述

EFFECT OF SOIL WATER AND NUTRIENTS ON PRODUCTIVITY OF KENTUCKY BLUEGRASS SYSTEM IN ACIDIC SOILS

The grasslands of the Appalachian region spread over undulating terrain with high annual precipitation rate which causes a large variation in soil and nutrient factors like water potential (WP), pH, nitrogen (N) and phosphorus (P) levels. There is a need to understand these factors and their interactive effects to design precise agronomic practices for acidic grasslands to maximize production. A pot experiment was conducted with an objective to quantify the effects of WP, pH, N and P rates on herbage accumulation and nutrient recovery of Kentucky bluegrass (Poa pratensis L.) cropping system. Centrally rotatable composite design was applied to study the effects of two levels of WP and five levels each of pH, N, and P fertilizer additions in order to optimize bluegrass herbage mass (yield). WP, pH, and N were significant main effects, as were the interactions WP × pH, WP × N, and pH × N. The yield response function was derived from these four factors. The order of importance for these model parameters based on their effect on herbage accumulation was WP > N > WP × pH > pH >WP × N > pH × N. The optimum levels of WP, soil pH, N, and P rates were predicted for Kentucky bluegrass by using the response surface yield model of this pot study i.e., WP of −422 kPa to −166 kPa, 5.5–6.1 soil pH, 50–68 N mg kg−1, 36–40 P mg kg−1. Concentration (%) of nutrients like N, P, potassium (K), calcium (Ca), and magnesium (Mg) were determined to study the impact of WP, pH, N, and P factors and their interactions on plant nutrient recovery. Main effects like WP, pH, and N levels had significant influence on N and P concentration in plant tissue. K, Ca, and Mg concentrations in plant tissue were significantly affected by WP, pH and their interaction. The results of this greenhouse study imply the necessity to incorporate the information about the variation of soil and nutrient factors in designing precise agronomic practices to low productive acid reclaimed grasslands with undulating topography and high annual precipitation rate.

Acidity Decay of Above-Drainage Underground Mines in West Virginia

Acidity of water from abandoned underground mines decreases over time, and the rate of decrease can help formulate remediation approaches and treatment system designs. The objective of this study was to determine an overall acidity decay rate for above-drainage underground mines in northern West Virginia from a large data set of mines that were closed 50 to 70 yr ago. Water quality data were obtained from 30 Upper Freeport and 7 Pittsburgh coal seam mines in 1968, 1980, 2000, and 2006, and acidity decay curves were calculated. The mean decay constant, k, for Upper Freeport mines was 2.73 x 10(-2) yr(-1), with a 95% confidence interval of +/- 0.0052, whereas the k value for Pittsburgh mines was not significantly different at 4.26 x 10(-2) yr(-1) +/- 0.017. Acidity from the T&T mine, which was closed 12 yr ago, showed a k value of 11.25 x 10(-2) yr(-1). This higher decay rate was likely due to initial flushing of accumulated metal salts on reaction surfaces in the mine, rapid changes in mine hydrology after closure, and treatment. Although each site showed a specific decay rate (varying from 0.04 x 10(-2) yr(-1) to 13.1 x 10(-2) yr(-1)), the decay constants of 2.7 x 10(-2) yr(-1) to 4.3 x 10(-2) yr(-1) are useful for predicting water quality trends and overall improvements across a wide spectrum of abandoned underground mines. We found first-order decay models improve long-term prediction of acidity declines from above-drainage mines compared with linear or percent annual decrease models. These predictions can help to select water treatment plans and evaluate costs for these treatments over time.

Predicting release of total dissolved solids from overburden material using acid-base accounting parameters

The Appalachian coal industry has been successful in developing technologies to identify, handle, treat and isolate potentially acid-forming overburden materials at coal mines in the region. Modern coal mining permits have stringent guidelines for reclamation and water discharge limits. Total dissolved solids (TDS) is a new water quality parameter that has been linked to a decrease in survival of aquatic macro-invertebrates in receiving streams. Past techniques to predict acid mine drainage potential to decrease impacts to streams may not accurately predict the release of TDS. The objective of this work was to develop a TDS release index from overburden material that could be used to predict and screen overburden materials that contribute to high TDS concentrations. Forty-one overburden samples containing a range of sandstones and shales were collected from surface mines in West Virginia, Virginia, and Kentucky. Samples were ground to <2 mm particle size and weathered in dilute HNO3 to determine TDS released. Supernatants were analyzed for pH, electrical conductivity (EC), and other selected ions. Results were compared to Acid-Base Accounting parameters for each sample; i.e. paste pH, maximum potential acidity (MPA), neutralization potential (NP), and net neutralization potential (NNP). Results showed that MPA (sulphur content) had the strongest relationship to TDS release, and low, moderate, and high TDS release indices were developed based on MPA values. Samples with MPA values of 0.0–1.0 g kg-1 gave <150 mg l-1 TDS, 1.0–3.0 g kg-1 gave <300 mg l-1, whereas 3.0+ g kg-1 produced TDS values >500 mg l-1. NPP was also a predictor for TDS, with an NPP ≥-2.0 g kg-1 likely to produce <300 mg l-1 of TDS and NPP <-2.0 g kg-1 likely to produce TDS concentrations >300 mg l-1.

Early C Sequestration Rate Changes for Reclaimed Minesoils

Abstract Reclaimed minesoils have well-defined ages (time since reclamation), making them suitable for studying temporal changes in terrestrial carbon sequestration. The objective of this research was to assess the effect of time since reclamation on soil organic carbon (SOC) sequestration and related soil properties such as texture, bulk density, and cation exchange capacity in three West Virginia minesoils along a chronosequence. The minesoils’ surface 750 Mg ha−1 (0–6 cm) was sampled at 1, 4, and 21 years and again at 2, 5, and 22 years postreclamation, giving a total of 6 site-years of information. Average SOC stocks (Mg C ha−1) were highest in the oldest minesoils. Soil bulk density was highest and unrelated to SOC concentration in the youngest minesoil, reflecting recent compressive reclamation techniques. The cation exchange capacity of older minesoils was influenced more by SOC than by clay, whereas the opposite was observed in younger minesoils. The relationship of SOC stock to time since reclamation was best described by a logarithmic diminishing returns model. Short-term (1 year) SOC sequestration rates (Mg C ha−1 y−1) were not appropriate to describing the change in SOC sequestration rate occurring along the chronosequence. When taken as the first derivative of the diminishing returns model, long-term SOC sequestration rates were shown to decline precipitously (80%) in the first 5 years after reclamation. The model predicts that the surface 750 Mg ha−1 of minesoil will contain about 13.3 Mg SOC ha−1 at 50 years after reclamation. About 75% of that SOC storage is predicted to be achieved in the first decade after reclamation.

Land Use Effects on Sample Size Requirements for Soil Organic Carbon Stock Estimations

Soil organic carbon (SOC) stock (in metric tons of carbon per hectare) is calculated from SOC concentration (in grams per kilogram) and soil bulk density (&rgr;b; in grams per cubic centimeter). Temporal changes in SOC stock are used to calculate terrestrial carbon sequestration rates used in global climate change models. The inherent variability in soil properties like SOC and &rgr;b means that larger sample sizes may be needed to accurately determine SOC stocks. Our objective was to calculate the minimum sample size required to detect changes in &rgr;b, SOC, and SOC stock for two land uses. Surface soils (0-5 cm) from two reclaimed mine soils and two managed hay fields in northern West Virginia were intensively sampled (60-74 samples each). Mean SOC and SOC stock values were larger in the hay fields (40 g/kg, 29 Mg ha−1) than in the mine soils (20 g/kg, 20 Mg ha−1), but &rgr;b was larger in reclaimed mine soils (1.4 g cm−3) than in hay field soils (1.2 g cm−3). The &rgr;b variance was larger in mine soils than that in hay field soils, but field variances for a given land use were similar (0.09 and 0.11 [g cm−3]2 in mine soils; 0.02 and 0.03 [g cm−3]2 in hay field soils). The variances in SOC concentration and SOC stock were not related to land use and were not similar within a land use. As a result, the minimum number of samples required to detect a change in &rgr;b, SOC, and SOC stock was a site-specific property and cannot be assumed a priori.

EFFECT OF COSOLVENTS ON Ca-Na EXCHANGE ONTO WYOMING BENTONITE

Calcium-sodium exchange on Wyoming bentonite in methanol, ethanol and acetone-water systems were investigated at 0.03 N Cl and at room temperature. Calcium-sodium exchange isotherms were plotted at cosolvent concentrations ranging from 0 to 70% wt./wt. using Ca and Na ionic activities before and after correction for CaCl+ formation. In both cases and in all treatments, a greater selectivity of bentonite surfaces for Ca ions was observed. When compared to water, different trends were observed among and within cosolvents. These trends varied depending on whether or not CaCl+ formation was accounted for. Ignoring the formation of CaCl+, the preference of bentonite for Ca increased in methanolwater systems with increased percent methanol at low equivalent Ca fraction (<0.2). At higher Ca fractions, this preference matched that of water. In ethanol-water, no increased preference of the surface for Ca was observed. In acetone-water, increasing cosolvent concentration decreased the preference of the surface for Ca. The magnitude of this decrease was larger at low equivalent Ca fraction (<0.2). After correction for CaCl+, both in solution and on the surface, the preference of bentonite for Ca2+ was larger in methanol- and ethanol-water systems. In acetone-water, increased surface preference for Ca was only apparent at low acetone fractions (<50%). At higher acetone fractions, there was evidence of increased Na loading but no increase in Ca2+ selectivity. Clearly, ion-pair formation and its effects on Ca-Na exchange reactions cannot be ignored in mixtures of aqueous-organic solvents. After accounting for this effect, Ca-Na exchange in the studied solvents appears to be more of a surface- than a solution-controlled phenomenon that involves both electrostatic and specific solvent-surface types of interactions that have not been elucidated.

Water Quality Improvements Over Time and Longevity of Acid Mine Discharges From Underground Mines in Northern West Virginia

About 90 percent of the untreated acid mine drainage in the northern Appalachian coal originates in underground mines. These mines were developed and abandoned before laws were enacted that require reclamation, sealing and closure, and water treatment. Since no one is legally responsible for treating this water, treatment may never occur and pollution from these sites will impact streams for decades. Changes in water quality from underground mine discharges over several decades was investigated, and the decay rate of sulfate discharge from these sites was evaluated. Water quality data was collected from underground mines that were sampled in 1999, and correlated to data collected during a 1968 study. The mines discharging acidity were characterized as to geology and coal seam, size of the mine, volume of coal removed during operation, age, and other factors. All eleven mine discharges improved in acidity and sulfate concentrations between the 1968 and 1999 samplings. A 2 percent decay rate was determined by I) calculating the decline of sulfate concentration between these two dates, 2) calculating sulfate declines from data of two other sources, and 3) back-calculating to the. original amount of coal remaining in the mine. This number is important because it allows for the calculation oflong-term trends of water discharging from underground mines and will help in remediation schemes. Additional

Temporal trends in Ca, Mg and K concentrations of grassland and garden soils in West Virginia, U.S.A. between 1986 and 1999

The effects of acidic deposition on agricultural soils have not received much attention because they are regularly limed and receive acid forming fertilizers far in excess of what would accumulate in these soils from atmospheric acidic deposition. However, not all agricultural soils are managed with equal intensity, and some may be prone to element specific effects from acidic deposition. Using data from the West Virginia University Soil Testing Laboratory and the National Atmospheric Deposition Program,it was found that soil Mg concentrations were decreasing up to 2.6% yr-1 in hay and pasture soils where acidic deposition was the highest. Rainfall amounts and biomass removaldid not appear to be related to this effect. By comparison, no trends in Mg depletion with acidic deposition were found for the more intensely managed home garden soils. Nor were there regional trends in Ca or K for either hay and pasture or home garden soils. While the correlation Mg depletion and acidic deposition does not in and of itself indicate causality, it does suggest the Mg status of unmanaged or moderately managed grasslands may be adversely affected by acidic deposition.

Grouping Soils by Taxonomic Order to Improve Lime Recommendations

The success of a liming program is dependent upon the accuracy of the lime recommendation, which in turn depends on the quality of the underlying correlations and calibrations. Because of the expense, large-scale field calibration experiments are rarely conducted. The relatively low economic returns from pastures make it even more unlikely that a calibration experiment would be conducted, especially in West Virginia. Therefore, any improvements in lime recommendations have to be made from lime correlations. Moreover, it is unlikely that a single lime correlation can accurately identify appropriate lime rates for all soils. Hence, the objectives of this study were to improve the accuracy of lime recommendations by using quick tests that account for soil order and to develop lime correlations for acidic pasture soils of West Virginia. Twenty-five surface soil samples (0–7.5 cm) from the three major soil orders in the state (Alfisols, Inceptisols, Ultisols) were collected, most in cooperation with state soil scientists. Standard procedures for the determination of lime requirements by the Adams–Evans buffer (AEB), Mehlich single buffer (MB), and Shoemaker–McLean–Pratt single buffer methods (SMPB) were used. Statistically significant improvements in lime recommendations for target pH values of 6.5 and 5.5 were achieved by accounting for soil order. Mehlich single buffer recommendations were better for Alfisols and Ultisols than for Entisols to achieve pH 6.5. Lime correlations were developed for all three chemical buffers by multiple regression where the independent variables were target pH and soil-buffer pH. The AEB predicted lime rates better for target pH 5.5.