Arsenic concentration in porewater of an alkaline coal ash disposal site: Roles of siderite precipitation/dissolution and soil cover

The geochemical behavior of As in porewaters of an alkaline coal ash disposal site was investigated using multilevel samplers. The disposal site was in operation from 1983 until 1994 and was covered with 0.3–0.5 m thick soils in 2001 when this study was initiated. Sequential extraction analyses and batch leaching experiments were also performed using the coal ash samples collected from the disposal site. The results suggest the important roles of siderite (FeCO₃) precipitation/dissolution and soil cover, which have been ignored previously. Arsenic levels in the porewater were very low (average of 10 μg L⁻¹) when the site was covered with soil due to coprecipitation with siderite. The soil cover enabled the creation of anoxic conditions, which raised the Fe concentration by the reductive dissolution of Fe-(hydr)oxides. Because of the high alkalinity generated from the alkaline coal ash, even a small increase in the Fe concentration (0.66 mg L⁻¹ on average) could cause siderite precipitation. When the soil cover was removed, however, an oxidizing condition was created and triggered the precipitation of dissolved Fe as (hydr)oxides. As a result, the dissolution of previously precipitated As-rich siderite caused higher As concentration in the porewater (average of 345 μg L⁻¹).     

Transport and fate of organic wastes in groundwater at the Stringfellow hazardous waste disposal site, southern California

In January 1999, wastewater influent and effluent from the pretreatment plant at the Stringfellow hazardous waste disposal site were sampled along with groundwater at six locations along the groundwater contaminant plume. The objectives of this sampling and study were to identify at the compound class level the unidentified 40-60% of wastewater organic contaminants, and to determine what organic compound classes were being removed by the wastewater pretreatment plant, and what organic compound classes persisted during subsurface waste migration. The unidentified organic wastes are primarily chlorinated aromatic sulfonic acids derived from wastes from DDT manufacture. Trace amounts of EDTA and NTA organic complexing agents were discovered along with carboxylate metabolites of the common alkylphenolpolyethoxylate plasticizers and nonionic surfactants. The wastewater pretreatment plant removed most of the aromatic chlorinated sulfonic acids that have hydrophobic neutral properties, but the p-chlorobenzene-sulfonic acid which is the primary waste constituent passed through the pretreatment plant and was discharged in the treated wastewaters transported to an industrial sewer. During migration in groundwater, p-chlorobenzenesulfonic acid is removed by natural remediation processes. Wastewater organic contaminants have decreased 3- to 45-fold in the groundwater from 1985 to 1999 as a result of site remediation and natural remediation processes. The chlorinated aromatic sulfonic acids with hydrophobic neutral properties persist and have migrated into groundwater that underlies the adjacent residential community.     

The impact of an open waste disposal site on soil and groundwater pollution

A study has been carried out of a waste disposal site, located in the valley of a small creek, 3 km south of Canakkale city centre. The surface area of the site was around 101000 square metres, and the total amount of waste deposited at the site since 1990 was approximately 1001000 tons. The major risks of the dump are its closeness to the university campus area to the south, the airport to the north, and residential areas encroaching towards the dump site. The nuisance caused by odour is high. The waste pile emplaced at the head of the tributary stream has caused channelling of the leachate to the creek, which is eventually washed towards the agricultural fields. The field investigation included surface geological, hydrogeochemical and geochemical studies. Water samples were collected at 11 points. Three observation wells were dug in front of the open waste disposal site. Soil samples from these observation wells were collected at 30, 70 and 150 cm depths, and some heavy metals were analysed. The concentrations of lead, copper and zinc in soil at the depth of 150 cm decreased with distance from the waste disposal site. Hydrogeochemical data analysis gave similar results.     

Study of contaminant transport at an open-tipping waste disposal site

Field and laboratory studies were conducted to estimate concentration of potential contaminants from landfill in the underlying groundwater, leachate, and surface water. Samples collected in the vicinity of the landfill were analyzed for physiochemical parameters, organic contaminants, and toxic heavy metals. Water quality results obtained were compared from published data and reports. The results indicate serious groundwater and surface water contamination in and around the waste disposal site. Analysis of the organic samples revealed that the site contains polychlorinated biphenyls and other organo-chlorine chemicals, principally chloro-benzenes. Although the amount of PCB concentration discovered was not extreme, their presence indicates a potentially serious environmental threat. Elevated concentrations of lead, copper, nickel, manganese, cadmium, and cobalt at the downgradient indicate that the contamination plume migrated further from the site, and the distribution of metals and metals containing wastes in the site is nonhomogeneous. These results clearly indicate that materials are poorly contained and are at risk of entering the environment. Therefore, full characterization of the dump contents and the integrity of the site are necessary to evaluate the scope of the problem and to identify suitable remediation options.     

Study of the use of coal fly ash as an additive to minimise fluoride leaching from FGD gypsum for its disposal

The use of coal fly ash as a fluoride retention additive has been studied as a way of treating flue gas desulphurisation (FGD) gypsum for its disposal in landfills. With this end leaching studies following the standard EN-12457-4 [Characterization of waste- Leaching-Compliance test for leaching of granular waste materials and sludges - Part 4: One stage batch test at a liquid to solid ratio of 10l/kg for materials with particle size below 10mm (without or with size reduction)] have been performed on FGD gypsum samples treated with different proportions of fly ash (0.1-100%). It was found that the fluoride leachable content in FGD gypsum was reduced in the range 1-55%, depending on the fly ash proportion added to FGD gypsum. High levels of fluoride leaching reduction (close to 40%) were achieved even at relatively low fly ash additions (5%). So, low fly ash incorporations assure the characterization of this by-product as a waste acceptable at landfills for non-hazardous wastes according to the Council Decision 2003/33/EC [Council Decision 2003/33/EC of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC] on waste disposal. Furthermore, the effectiveness of the proposed FGD gypsum stabilization method was also studied in column leaching systems, proving its good performance in simulated conditions of disposal. In such conditions a fluoride leaching reduction value slightly higher than 25% was displayed for a fly ash added amount of 5%.     

铁锰胶体对地下水中无机磷的吸附-脱附特性

地下水中磷富集已成为水体富营养化的重要污染来源之一,但对于地下水中磷的污染过程认识不清。本研究对比了地下水中常见4种铁锰胶体(水铁矿胶体、针铁矿胶体、二氧化锰胶体和水钠锰矿胶体)对无机磷的吸附和脱附性能的差异。结果表明：铁锰胶体对磷的吸附主要是单分子层的化学吸附,锰胶体吸附量与吸附速率均大于铁胶体,中性pH和较高离子强度有利于铁锰胶体对磷的吸附,但有机质的存在会大大降低对磷的吸附量,尤其是针铁矿胶体受有机质的影响程度最大,其中腐殖酸影响比富里酸更大。同时,钙离子对磷从铁锰胶体上的脱附影响高于钠离子,且铁胶体的脱附效率高于锰胶体。以上研究结果为理解地下水中磷污染过程提供数据支撑。     

Chemical reactions of uranium in ground water at a mill tailings site

We studied soil and ground water samples from the tailings disposal site near Tuba City, AZ, located on Navajo sandstone, in terms of uranium adsorption and precipitation. The uranium concentration is up to 1 mg/l, 20 times the maximum concentration for ground water protection in the United States. The concentration of bicarbonate (HCO₃⁻) in the ground water increased from ≤7×10⁻⁴ M, the background concentration, to 7×10⁻³ M. Negatively charged uranium carbonate complexes prevail at high carbonate concentrations and uranium is not adsorbed on the negatively charged mineral surfaces. Leaching experiments using contaminated and uncontaminated sandstone and 1 N HCl show that adsorption of uranium from the ground water is negligible. Batch adsorption experiments with the sandstone and ground water at 16°C, the in situ ground water temperature, show that uranium is not adsorbed, in agreement with the results of the leaching experiments. Adsorption of uranium at 16°C is observed when the contaminated ground water is diluted with carbonate-free water. The observed increase in pH from 6.7 to 7.3 after dilution is too small to affect adsorption of uranium on the sandstone. Storage of undiluted ground water to 24°C, the temperature in the laboratory, causes coprecipitation of uranium with aragonite and calcite. Our study provides knowledge of the on-site uranium chemistry that can be used to select the optimum ground water remediation strategy. We discuss our results in terms of ground water remediation strategies such as pump and treat, in situ bioremediation, steam injection, and natural flushing.     

Application of surface-deposition models to size-fractionated coal fly ash

Stack fly ash emitted from a large, coal-fired power plant was separated in situ into 8 or 12 discrete fractions with inertial cascade impactors. The fractions, ranging in size from 0.1 to 50 μm and including three fractions with aerodynamic mass dia. ≥ 1 μm, were previously analyzed for up to 43 elements by instrumental neutron-activation analysis. In this report geometric and theoretical surface deposition models are used to estimate the depth of the surface layer as well as the concentrations of enriched elements in the surface layer. The results indicate that the thickness of the surface layer is small, even at particle sizes of 0.1 μm where it is estimated to be about 20% of the particle diameter. The behavior of the relative concentrations of surface-enriched elements as a function of particle size was consistent with the slip-flow regime of aerosol mechanics.     

Occurrence and attenuation of specific organic compounds in the groundwater plume at a former gasworks site

The changing contaminant pattern with travelled distance was investigated in the anaerobic groundwater plume downstream from an extended zone containing residual NAPL at a former gas manufacturing plant. With increasing distance, O- and N-heterocyclic aromatic compounds are enriched in the plume relative to the usually assessed coal tar constituents (poly- and monocyclic aromatic compounds). In a first approximation, the overall concentration decrease of the investigated compounds follows a first order overall decay. The half life distance in the plume downgradient from the source varied between 20 m for benzene and up to 167-303 m for alkyl-naphthalenes. Acenaphthene is degraded only within about 50 m downstream from the source area, then its concentration remains constant (ca. 180 microg/l) and far above the legal limit. Dimethyl-benzofurans were the most recalcitrant among all compounds which could be quantified with the analytical method available. The overall groundwater contamination in the plume is seriously underestimated if only BTEX and 16-EPA-PAHs are monitored.     

Activity-dependent labeling of oxygenase enzymes in a trichloroethene-contaminated groundwater site

A variety of naturally occurring bacteria produce enzymes that cometabolically degrade trichloroethene (TCE), including organisms with aerobic oxygenases. Groundwater contaminated with TCE was collected from the aerobic region of the Test Area North site of the Idaho National Laboratory. Samples were evaluated with enzyme activity probes, and resulted in measurable detection of toluene oxygenase activity (6-79% of the total microbial cells). Wells from both inside and outside contaminated plume showed activity. Toluene oxygenase-specific PCR primers determined that toluene-degrading genes were present in all groundwater samples evaluated. In addition, bacterial isolates were obtained and possessed toluene oxygenase enzymes, demonstrated activity, and were dominated by the phylotype Pseudomonas. This study demonstrated, through the use of enzymatic probes and oxygenase gene identification, that indigenous microorganisms at a contaminated site were cometabolically active. Documentation such as this can be used to substantiate observations of natural attenuation of TCE-contaminated groundwater plumes.     

Sulfur and carbon cycling in a flue gas desulfurization sludge disposal site

Products of a power plant flue gas desulfurization scrubber are discharged into a pond as sludge consisting of calcite (initial delta13C 3.2-3.8 per thousand), gypsum (initial delta34S 7.6-8.6 per thousand), and aqueous solution. Reducing conditions exist below a boundary that appears to move vertically as a function of changes in pond water level. Under reducing conditions, bacteria partially reduce aqueous sulfate to low-delta34S sulfide, consuming organic carbon and generating low-delta13C bicarbonate. Under oxidizing conditions, sulfide is converted to sulfate, leading to calcite dissolution, gypsum precipitation, and isotopic re-equilibration of remaining calcite with dissolved bicarbonate near the pond surface. The gypsum has delta34S near 6 per thousand, and calcite has delta13C as low as -1.7 per thousand; the changes from initial values correspond to predictions based on isotopic balance and reaction stoichiometry. The pond largely contains the products of bacterial reduction. After the pond is abandoned, these products may adversely affect attempts to revegetate the site. Future bacterial reduction may be best controlled by dewatering and limiting the supply of organic matter in percolating surface water.     

Degradation of organophosphoric esters in leachate from a sea-based solid waste disposal site

Degradation of organophosphoric esters (OPEs) in leachate from a sea-based solid waste disposal site was investigated by laboratory experiment. Aryl-phosphates, tricresyl phosphate and triphenyl phosphate, in leachate rapidly decreased to less than the detection limit within 20 days under aerobic condition, suggesting high biodegradability. These phosphates also decreased in sterilized leachate, which suggested a contribution to degradation by reactions (adsorption and chemical degradation) with chemicals in the leachate. Concerning alkyl-phosphates, tributyl phosphate decreased rapidly after one week, which is considered to have been caused by biodegradation. Tris-2-ethylhexyl phosphate and tris-2-butoxyethyl phosphate decreased slowly in all samples but that of sterilized distilled water. This however, suggested contribution of biodegradation because the velocity of decrease in the leachate was higher than in control samples. Among chloro alkylphosphates, decrease of tris-2-chloroethyl phosphate and tris-dichloropropyl phosphate were observed though it was not obvious whether by biodegradation or not. Decrease of tris-2-chloropropyl phosphate (TCPP) was not observed for 80 days suggesting that TCPP remains in the leachate over a long period of time. Except for aryl-phosphates decrease of OPEs was not observed under anaerobic condition. It was considered that the composition ratio and the behavior of OPEs in leachate in the field reflects the biological and chemical degradation as well as the chemical properties of OPEs.     

Dynamic purification of coal ash by a gas-solid fluidized bed

Fluidized bed filtration classified as granular bed filtration is a solution for removing particles from flue gas. Fine particles are captured by colliding with bed material. Binary mixtures including fines exist in the fluidized bed; the situation becomes more complex because the fines increases with time as particles enter continuously. Coal ash was put into the inlet gas of a gas-solid fluidized bed with silica sand and the variations in concentration with time was monitored, to elucidate the dynamic purification of fines by bed material and the interaction therewith. Water was injected into the inlet gas also to study the influence of water content on the removal of particles. Experimental results showed that the particle concentration rapidly increased with time until equilibrium was achieved. The outlet concentrations exceeded the inlet concentration (such that the removal efficiency was negative) at operating time between 26 and 30 min, yielding an efficiency as low as -35%. The removal efficiency increased with the relative humidity from 30% to 70%. The maximum cumulative collection ratios of particles (by mass) were 20%, 22% and 27% at humidities of 30%, 50% and 70%, declining to 7%, 13%, and 19% at the end.     

Heavy metal accumulation by Nicotiana glauca Graham in a solid waste disposal site

Nicotiana glauca Graham, is the only perennial shrub growing in a solid waste contaminated site in the Negev desert of Israel. The concentration of heavy metals (Cu, Fe, Mn, Zn, Ni, Cd and Pb) in the upper soil layer was significantly higher (p<0.01) than in non-contaminated desert soil. In root and shoot of N. glauca, growing in the site, the concentration of Cu, Zn and Fe was significantly higher (p<0.05) than in plants of a non-contaminated site. In a controlled experiment, the concentrations of Zn and Cu in root of plants grown, in a mixture of contaminated and non-contaminated soil (1:1) was 9.5 and 4.7 higher than that of plants grown in non-contaminated soil, respectively. While Zn was accumulated in shoot of plants grown in contaminated soil (531 mgkg(-1)) in significantly higher concentration than in plants grown in non-contaminated soil (56 mgkg(-1)), no significant differences were found in Cu accumulation. Growth of N. glauca was inhibited on contaminated soil, but no other obvious stress symptoms were apparent. Therefore, long term experiments under controlled conditions are planned to study the mechanism of heavy metal tolerance and accumulation in N. glauca.     

Dioxins,chlorophenols and other chlorinated organic pollutants in colloidal and water fractions of groundwater from a contaminated sawmill site

BACKGROUND, AIM, AND SCOPE: The distribution of chlorinated organic contaminants in groundwater and the importance of colloids were studied in groundwater from a sawmill site contaminated by chlorophenol preservatives. MATERIALS AND METHODS: The groundwater was fractionated into three different size ranges: (1) >0.7 mum, (2) 0.4-0.7 mum and (3) 0.2-0.4 mum and the filtered water phase. The concentrations of chlorophenols (CP), chlorinated phenoxy phenols (PCPP), chlorinated diphenyl ethers (PCDE), chlorinated dibenzofurans (PCDF) and chlorinated dibenzo-p-dioxins (PCDD) were determined in each fraction. The colloids were characterised regarding the chemical composition using X-ray photoelectron spectroscopy (XPS). RESULTS: Chlorophenols were mostly found in the water fraction and PCDD/Fs were found almost exclusively in the particulate fractions. For example, the filtered water phase contained 2,100 mug l(-1) and 0.72 ng l(-1) for CPs and PCDD/Fs, respectively, and the particulate fractions contained 27 mug l(-1) and 32 ng l(-1) for CPs and PCDD/Fs, respectively. XPS evaluation of the particulate phases showed no correlation between the surface chemistry of the particle properties and the distribution of chlorinated compounds. DISCUSSION: The results suggest that groundwater transport of CPs, PCPPs, PCDEs and PCDD/Fs may occur from contaminated sawmill sites and that the colloid-facilitated transport, especially of PCDD/Fs, is substantial. The results correlated well with previous studies of compounds sorbed to dissolved organic carbon, which indicate that dissolved and colloidal organic carbon facilitated the transport of PCDEs, PCDFs and PCDDs particularly. CONCLUSIONS: Several classes of chlorinated compounds were readily detected in the groundwater samples. Due to the differences in their physicochemical properties, CPs, PCPPs, PCDEs and PCDD/Fs vary in their partitioning between colloidal fractions and the filtered groundwater. The proportion of the bound fraction increased with an increasing hydrophobicity of the chlorinated compounds. The groundwater transport of colloid-associated pollutants from the site may be significant. RECOMMENDATIONS AND PERSPECTIVES: The results imply that colloidal particles <0.7 mum are freely mobile in groundwater from this site. The groundwater transport of colloid-associated pollutants may be significant. However, the extent of the problem is not yet known and, thus, further research is needed to evaluate the impact of colloidal transport of hydrophobic organic contaminants. In Sweden alone, 400 to 500 sawmill sites are estimated to be contaminated with PCDD/Fs as a result of the former use of CP-based wood preservatives. The widespread use of CP mixtures for a variety of applications, including wood preservation, indicates that potential colloidal transport will be an issue of concern in many countries.     

Mobilization of arsenic from subsurface sediments by effect of bicarbonate ions in groundwater

Arsenic leaching by bicarbonate ions has been investigated in this study. Subsurface sediment samples from Bangladesh were treated with different carbonate and bicarbonate ions and the results demonstrate that the arsenic leaching efficiency of the carbonate solutions decreased in the order of Na2CO3>NaHCO3>BaCO3>MnCO3. Sodium carbonate and bicarbonate ions extracted arsenic most efficiently; Na2CO3 leached maximum 118.12 microg/l of arsenic, and NaHCO3, 94.56 microg/l of arsenic from the Ganges delta sediments after six days of incubation. The arsenic concentrations extracted in the batch experiments correlated very well with the bicarbonate concentrations. The kinetics study of arsenic release indicates that arsenic-leaching rate increased with reaction time in bicarbonate solutions. Bicarbonate ions can extract arsenic from sediment samples in both oxic and anoxic conditions. A linear relationship found between arsenic contents in core samples and those in leachates suggests that dissolved arsenic concentration in groundwater is related to the amount of arsenic in aquifer sediments. In batch experiment, bicarbonate solutions effectively extracted arsenic from arsenic adsorbed iron oxyhydroxide, reflecting that bicarbonate solutions may mobilize arsenic from iron and manganese oxyhydroxide in sediments that are ubiquitous in subsurface core samples. Carbonate ion may form complexes on the surface sites of iron hydroxide and substitute arsenic from the surface of minerals and sediments resulting in release of arsenic to groundwater. Like in the batch experiment, arsenic and bicarbonate concentrations in groundwater of Bangladesh correlated very well. Therefore, bicarbonate leaching is presumed to be one important mechanism to mobilize arsenic in bicarbonate dominated reducing aquifer of Bangladesh and other parts of the world as well.     

Transport of reactive colloids and contaminants in groundwater: effect of nonlinear kinetic interactions

Transport of reactive colloids in groundwater may enhance the transport of contaminants in groundwater. Often, the interpretation of results of transport experiments is not a simple task as both reactions of colloids with the solid matrix and reactions of contaminants with the solid matrix and mobile and immobile colloids may be time dependent and nonlinear. Further colloid transport properties may differ from solute transport properties. In this paper, a one-dimensional model for coupled and contaminant in a porous medium (COLTRAP) is presented together with simulation results. Calculated breakthrough curves (BTC's) during contamination and decontamination show systematically the effect of nonlinear and kinetic interactions on contaminant transport in the presence of reactive colloids, and the effect of colloid transport properties that differ from solute transport properties. It is shown that in case of linear kinetic reactions, the rate of exchange of mobile and immobile colloids have a large impact on the shape of BTC's even if the solid matrix is saturated with respect to colloids. BTC's during the contamination and decontamination phase have identical shapes in this case. Moreover, the slow reactions of contaminants and colloids may lead to unretarded breakthrough of contaminants. Independent of reaction rates, nonlinear reactions lead to BTC's that are steeper during contamination than in the linear case. A characteristic aspect of nonlinear sorption is that shapes of BTC's differ during the contamination and decontamination phase. It has been observed that shapes of some of the simulated adsorption and desorption curves are similar as shapes found in experiments reported in literature. This stresses the importance of incorporating both kinetics and nonlinearity in models for coupled colloid and contaminant transport and the capability of COLTRAP to interpret experimental results. Finally, to figure out whether nonlinear processes play a role, it is very important to consider both contamination and decontamination in transport experiments.     

Multi-component reactive transport modeling of natural attenuation of an acid groundwater plume at a uranium mill tailings site

Natural attenuation of an acidic plume in the aquifer underneath a uranium mill tailings pond in Wyoming, USA was simulated using the multi-component reactive transport code PHREEQC. A one-dimensional model was constructed for the site and the model included advective-dispersive transport, aqueous speciation of 11 components, and precipitation-dissolution of six minerals. Transport simulation was performed for a reclamation scenario in which the source of acidic seepage will be terminated after 5 years and the plume will then be flushed by uncontaminated upgradient groundwater. Simulations show that successive pH buffer reactions with calcite, Al(OH)3(a), and Fe(OH)3(a) create distinct geochemical zones and most reactions occur at the boundaries of geochemical zones. The complex interplay of physical transport processes and chemical reactions produce multiple concentration waves. For SO4(2-) transport, the concentration waves are related to advection-dispersion, and gypsum precipitation and dissolution. Wave speeds from numerical simulations compare well to an analytical solution for wave propagation.     

Seasonal patterns of the bacterioplankton community composition in a lake threatened by a pesticide disposal site

Background aim and scope  

The objective of the study was to determine the effects of ca. 35 years of pesticide contamination (pesticide dump—PD) of Lake Szeląg Wielki (located in the north-eastern Poland) on changes in the microbial communities of aquatic ecosystems. In the years 2008–2009, analyses were carried out for seasonal changes in the quantity and composition of bacterioplankton in the lake examined, which is of high significance to the tourism and fishing industries and is located in the vicinity of an area subjected to reclamation after a pesticide dump.