Soil properties and water regime of reclaimed surface dumps in the North Bohemian brown-coal region--a field study

This paper attempts to characterise the water regime of reclaimed surface dumps in connection with their soil physical properties. The results of a research project based on field measurements of moisture content and hydraulic conductivity, supported by analyses of undisturbed soil samples, led to recommendations regarding technological procedures for such dumps. A dielectric soil moisture meter, in an improved version, was successfully used for field monitoring and further evaluation of moisture content. Hydraulic conductivity was also measured in the field (by repeated borehole infiltration) using the Guelph permeameter method. Laplace-Gardner analysis was used for evaluating the field saturated hydraulic conductivity results.     

Leaching Induced Changes in Substrate and Solution Chemistry of Mine Soil Microcosms

Leaching of soluble salts formed as the result of pyrite oxidation and primary mineral weathering is a major process in mine soil development. A microcosm experiment was designed to study leaching rates from mine soil columns under controlled laboratory conditions. Objectives of this experiment were to investigate the effect of leaching and the effect of fly ash amelioration on mid- to long-term chemical soil properties, and to test whether the results are qualitatively comparable to long-term field studies along a site chronosequence. The leaching experiment was conducted over a period of 850 days representing a kind of time-lapse picture due to high water fluxes. Leaching resulted in more favourable mid- to long-term properties of mine site topsoils, especially a reduced risk for acidity and salt stress. Ash amelioration decreases leaching rates by increasing pH and Al and Fe precipitation. It could be shown that the results of the column leaching studies are qualitatively in good agreement with field observations at least for long-term considerations. By enhancing the leaching process mid- to long-term chemical soil properties can be estimated.     

Chemical investigations of aquifers affected by pyrite oxidation in the Bitterfeld lignite district

In a large area around the former open-pit lignite mines near Bitterfeld, Germany, groundwater taken from wells was analyzed for the major cations, anions, and trace elements. Quaternary and Tertiary sediments were collected from aquifers exposed on the sides of the pits and from boreholes outside the mines and analyzed for major and trace elements, as well as for carbonate, pyritic sulfur and total organic carbon. The pH and electrical conductivity of the sediments in suspension were measured. Significant differences were determined between the Tertiary sediments of the aquifers that were exposed to atmospheric oxygen during the lowering of the groundwater table and those outside the cone of depression. The greatest differences were found in the pyrite content, the pH values, and the electrical conductivity. In order to map the degree to which the mining of the lignite has affected the quality of the groundwater in the study area, the water samples were divided into six classes on the basis of their sulfate content. The neutralization potential was calculated to estimate the potential for acidification. Prediction of future groundwater quality is based on both (i) the present composition of the groundwater, surface water, and Quaternary and Tertiary aquifer sediments and (ii) the present and future groundwater flow directions. These studies have shown which parameters are important for future groundwater monitoring.     

Hydrogen peroxide for physicochemically degrading petroleum-contaminated soils

Catalyzed hydrogen peroxide was applied to contaminated soil at an equipment storage yard in Reno, Nevada, that had also been used as a dump for motor oil and diesel fuel for twenty years. The site is only a quarter mile from the Truckee River—a principal source of Reno's drinking water. This article details hydrogen peroxide's advantages, disadvantages, costs, and treatment for reducing to below the 100 mg/kg Nevada action level the petroleum hydrocarbons in the yard's arid soil, which is characterized by low organic carbon content and low manganese oxide content.     

Leachate recirculation: moisture content assessment by means of a geophysical technique

Bioreactor technology is a waste treatment concept consisting in speeding up the biodegradation of landfilled waste by optimizing its moisture content through leachate recirculation. The measurement of variations in waste moisture content is critical in the design and control of bioreactors. Conventional methods such as direct physical sampling of waste reach their limits due to the interference with the waste matrix. This paper reviews geophysical measurements such as electrical direct current and electromagnetic slingram methods for measuring the electrical conductivity. Electrical conductivity is a property, which is linked to both moisture and temperature and can provide useful indications on the biodegradation environment in the waste mass. The study reviews three site experiments: a first experimentation shows the advantages (correlation between conductive anomaly and water seepage) but also the limits of geophysical interpretation; the two other sites allow the leachate recirculation to be tracked by studying the relative resistivity variation versus time from electrical 2D imaging. Even if some improvements are necessary to consider geophysical measurements as a real bioreactor monitoring tool, results are promising and could lead to the use of electrical 2D imaging in bioreactor designing.     

Leachate quality from iron-ore tailings leached with deionized water of different pH

Iron-ore tailings filled in a soil column were leached daily with deionized water at various pH 5, 6, 7, 8 and 9) for 50 days. There was a continuous decline in conductivity of all leachates during the study. The final conductivity values of all leachates were significantly lower (P < 0.001) than the initial values. Final pH values were all in the range 8.2–8.3. The lower pH treatments resulted in high leachate concentrations of magnesium, manganese, iron, lead, and zinc. Sodium, potassium and calcium concentrations were similar for all treatments.     

A simple and convenient empirical survey method with a soil electrical conductivity meter for incineration residue-derived soil contamination

To facilitate field surveys for identifying areas of incineration residue-derived soil contamination, a simple and convenient method with a soil electrical conductivity meter was examined. First, the leaching test specified by Notification No. 13 of the Ministry of the Environment, 1973, was conducted on 506 samples of 11 types of wastes and compost, and the relationship between the concentrations of toxic elements [total Hg (T-Hg), Cd, Pb, Cr⁶⁺, and As] and values of electrical conductivity (EC) was examined. The results showed that bottom ash and fly ash were wastes with high EC values and that these wastes indicated higher levels of toxic elements. Second, an estimation method for the soil EC value of contaminated soil (ECc) was proposed based on the EC values of noncontaminated soil, and its usefulness was examined. The results of field surveys conducted at sites whose soils were suspected of contamination by dioxins and other pollutants derived from incineration residues showed that the contaminated spots and areas were identified by using ECc values. Moreover, comparison of the elemental contents of soils in terms of Cr, Ni, Zn, Na, K, Ca, Fe, Mn, and others, in addition to the above-mentioned toxic elements (excluding Cr⁶⁺), with those of the potential sources of pollution was verified to be effective for identifying the source of soil contamination.     

Integrated geophysical surveys on waste dumps: evaluation of physical parameters to characterize an urban waste dump (four case studies in Italy).

Geophysical surveys were carried out on different waste dumps to evaluate key geometric and physical parameters. Depending on the dump dimensions and physical characteristics different geophysical techniques were used. Vertical electrical sounding, electrical resistivity tomography, induced polarization and seismic refraction techniques were integrated to eliminate the non-uniqueness of solutions and for a better understanding of the results. Physical parameters inside and outside the dumps were compared. The change of physical parameters such as resistivity, chargeability, and P-wave velocity allowed evaluation of waste dump geometry, leachate saturation levels, and thickness of waste. Furthermore, in illegal dumps, the size and waste type disposed could be evaluated. Calculated results were compared with plans and book-keeping from the dumps investigated.     

Indirect measurements of field-scale hydraulic conductivity of waste from two landfill sites

Management and prediction of the movement and distribution of fluids in large landfills is important for various reasons. Bioreactor landfill technology shows promise, but in arid or semi-arid regions, the natural content of landfilled waste may be low, thus requiring addition of significant volumes of water. In more humid locations, landfills can become saturated, flooding gas collection systems and causing sideslope leachate seeps or other undesirable occurrences. This paper compares results from two different approaches to monitoring water in waste. At the Brock West Landfill in eastern Canada, positive pore pressures were measured at various depths in saturated waste. The downward seepage flux through the waste is known, thus the vertical saturated hydraulic conductivity of the waste at this landfill was determined to be 3 × 10(-7)cm/s. By comparison, the Spadina Landfill in western Canada is predominantly unsaturated. The infiltration of moisture into the waste was measured using moisture sensors installed in boreholes which determined arrival time for moisture fronts resulting from major precipitation events as well as longer-term change in moisture content resulting from unsaturated drainage during winter when frozen ground prevented infiltration. The unsaturated hydraulic conductivity calculated from these data ranged from approximately 10(-6)cm/s for the slow winter drainage in the absence of significant recharge to 10(-2)cm/s or higher for shallow waste subject to high infiltration through apparent preferential pathways. These two very different approaches to field-scale measurements of vertical hydraulic conductivity provide insight into the nature of fluid movement in saturated and unsaturated waste masses. It is suggested that the principles of unsaturated seepage apply reasonably well for landfilled waste and that the hydraulic behavior of waste is profoundly influenced by the nature and size of voids and by the degree of saturation prevailing in the landfill.     

Improving the aeration of critical fine-grained landfill top cover material by vegetation to increase the microbial methane oxidation efficiency

The natural methane oxidation potential of methanotrophic bacteria in landfill top covers is a sustainable and inexpensive method to reduce methane emissions to the atmosphere. Basically, the activity of methanotrophic bacteria is limited by the availability of oxygen in the soil. A column study was carried out to determine whether and to what extent vegetation can improve soil aeration and maintain the methane oxidation process. Tested soils were clayey silt and mature compost. The first soil is critical in light of surface crusting due to vertical erosion of an integral part of fine-grained material, blocking pores required for the gas exchange. The second soil, mature compost, is known for its good methane oxidation characteristics, due to high air-filled porosity, favorable water retention capacity and high nutrient supply. The assortment of plants consisted of a grass mixture, Canadian goldenrod and a mixture of leguminous plants. The compost offered an excellent methane oxidation potential of 100% up to a CH₄-input of 5.6 l CH₄ m⁻² h⁻¹. Whereas the oxidation potential was strongly diminished in the bare control column filled with clayey silt even at low CH₄-loads. By contrast the planted clayey silt showed an increased methane oxidation potential compared to the bare column. The spreading root system forms secondary macro-pores, and hence amplifies the air diffusivity and sustain the oxygen supply to the methanotrophic bacteria. Water is produced during methane oxidation, causing leachate. Vegetation reduces the leachate by evapotranspiration. Furthermore, leguminous plants support the enrichment of soil with nitrogen compounds and thus improving the methane oxidation process. In conclusion, vegetation is relevant for the increase of oxygen diffusion into the soil and subsequently enhances effective methane oxidation in landfill cover soils.     

Effectiveness of resistivity monitoring for interpreting temporal changes in landfill properties

It is always possible for impermeable layers to exist in landfills. When they do, the properties of the solution at the exit of the leachate-collection system might not accurately reflect the overall properties of the landfill. This study examines whether resistivity monitoring is effective for determining the influence of impermeable layers on the leachate. The test cell used in this study was filled with waste made up mainly of incinerator ash and shredded incombustible material. Three lines of resistivity sensors were laid in the uppermost layer of the fill. A resistivity profile was recorded periodically from each of these lines. The water-table level and leachate properties were measured concurrently. Leachate conductivity was mainly controlled by concentrations of the main ions, and it correlated inversely to variations in resistivity. Temporal changes in the resistivity of the fills are an excellent means of assessing the leaching in fills. Monitoring the properties of leachate, combined with resistivity profiling, is extremely useful for interpreting the temporal changes of properties in landfills containing impermeable layers.     

Effect of nine years of animal waste deposition on profile distribution of heavy metals in Abeokuta,south-western Nigeria and its implication for environmental quality

Uncontrolled deposition of waste from animal farms is a common practice in south-western Nigeria, and the presence of heavy metals in soil constitutes environmental and health hazards by polluting the soil, ground water, adjoining streams and rivers. The study investigated the profile distribution of Mn, Pb, Cd, Zn, Fe, Cu, Ni and Cr in some tropical Alfisols in south-western Nigeria after nine years disposal of animal wastes. The amount of these metals in the soil horizons was high enough to cause health and phytotoxic risks. All the metals except Zn and Cr increased down the profile, while Mn, Pb, Cd, Fe, Cu and Ni accumulated at 80–120 cm depth. The increment of these metals at this depth over the top soil were 26%, 143%, 72%, 47%, 328% for Mn, Pb, Cd, Cu and Ni, respectively. It thus, shows their mobility and the possibility of polluting ground water. The Mn content at the poultry and cattle waste sites increased by 127% and 25%, respectively over the control, while that of cattle and swine dump site for Cd content were 9.82 and 15.63 mg kg^?1, respectively. Lead content also increased by 8.52 and 5.25 mg kg^?1, respectively.There was the accumulation of Zn and Cu at the swine dump site while the cattle dump site had the highest amounts of nickel and chromium. The least amount of Fe was recorded at the swine waste dump site. The reduction in organic matter with depths together with the reduced pH might have favored the mobility of the metals. The ranking of pollution among the sites was poultry > swine > cattle > sheep and could be due to the type of ration fed, the vaccination programmes, sanitation programmes and other management practices.     

Direct and Indirect Effects of Soil Pollution by Lignite Mining

Lignite mining and processing has caused a pronounced impact both directly and indirectly on soils and ecosystems across large areas of the former GDR. We studied soils of pine forest ecosystems at sites affected by severe alkaline dust and sulphur deposition, stemming from lignite fired power plant emission, and at dumped sites from lignite mining. In this paper we summarize our main results and evaluate the long-term impact of lignite mining and combustion on the environment. The pine ecosystems on naturally developed soils show a clear effect of deposition history along a former deposition gradient with distinct changes in chemical properties of organic surface layers and mineral soil as well as in element turnover and cycling rates. Afforested sites on mining dumps are directly affected by the composition of the dumped substrates. Over a large area (800 km²) these substrates are dominated by Tertiary sediments with varying amounts of lignitic particles and pyrite that result in phytotoxic site conditions (pH < 3, high salt and metal contents). High amelioration doses of liming material (up to 200 t ha⁻¹) were applied for restoration purposes. We studied the development of these sites over a period of 60 years using a false-time series approach. Beside the extreme soil conditions, element budgets of these sites are characterized by very high element release rates over decades caused by pyrite oxidation and primary mineral weathering.     

Mineralogical characterization of the Tournemire argillite after in situ interaction with concretes

This study aims to investigate, through mineralogical characterization (SEM, XRD) and mass-balance calculations, the effects of contact time, concrete types and presence of free water on the Tournemire argillite under in situ conditions. Three sampling zones from Excavation Disturbed Zone (EDZ) areas have been chosen: (1) dry contacts, collected at the tunnel masonry/argillite interface (contact time - 125 years), (2) wet contacts, taken close to drained areas below the tunnel roadbed in contact with the canal draining the Cernon fault water (contact time - 15 and 7 years) and at the tunnel masonry/argillite interface over 70 m from the Cernon fault (contact time - 125 years). This study shows that: in the absence of water, no significant modification of argillite is observed after 125 years, except for pyrite dissolution and gypsum precipitation; in the presence of water, precipitation of gypsum, recrystallization of mixed-layer clays, neoformation of zeolites and K-feldspars overgrowths are observed. At the concrete/argillite interface near the Cernon fault, important dolomite neoformation and leaching of chlorite and kaolinite occur. These processes are enhanced with contact time, low flow rate and the nature of the concrete (compound cement Portland CEM II 32.5). Evidence for oxidation processes linked to the EDZ (pyrite oxidation, Fe-oxy-hydroxide and gypsum precipitation) is observed.     

Scaling methane oxidation: from laboratory incubation experiments to landfill cover field conditions

Evaluating field-scale methane oxidation in landfill cover soils using numerical models is gaining interest in the solid waste industry as research has made it clear that methane oxidation in the field is a complex function of climatic conditions, soil type, cover design, and incoming flux of landfill gas from the waste mass. Numerical models can account for these parameters as they change with time and space under field conditions. In this study, we developed temperature, and water content correction factors for methane oxidation parameters. We also introduced a possible correction to account for the different soil structure under field conditions. These parameters were defined in laboratory incubation experiments performed on homogenized soil specimens and were used to predict the actual methane oxidation rates to be expected under field conditions. Water content and temperature corrections factors were obtained for the methane oxidation rate parameter to be used when modeling methane oxidation in the field. To predict in situ measured rates of methane with the model it was necessary to set the half saturation constant of methane and oxygen, K_m, to 5%, approximately five times larger than laboratory measured values. We hypothesize that this discrepancy reflects differences in soil structure between homogenized soil conditions in the lab and actual aggregated soil structure in the field. When all of these correction factors were re-introduced into the oxidation module of our model, it was able to reproduce surface emissions (as measured by static flux chambers) and percent oxidation (as measured by stable isotope techniques) within the range measured in the field.     

Water movement through an experimental soil liner

A field-scale soil liner was constructed to test whether compacted soil barriers in cover and liner systems could be built to meet the U.S. EPA saturated hydraulic conductivity requirement (⩽ 1 × 10⁻⁷ cm s⁻¹). The 8 × 15 × 0.9 m liner was constructed in 15 cm compacted lifts using a 20,037 kg pad-foot compactor and standard engineering practices. Water infiltration into the liner has been monitored for one year. Monitoring will continue until water break through at the base of the liner occurs. Estimated saturated hydraulic conductivities were 2.5 × 10⁻⁹, 4.0 × 10⁻⁸, and 5.0 × 10⁻⁸ cm s⁻¹ based on measurements of water infiltration into the liner by large- and small-ring infiltrometers and a water balance analysis, respectively.Also investigated in this research was the variability of the liner's hydraulic properties and estimates of the transit times for water and tracers. Small variances exhibited by small-ring flux data suggested that the liner was homogeneous with respect to infiltration fluxes. The predictions of water and tracer breakthrough at the base of the liner ranged from 2.4–12.6 y, depending on the method of calculation and assumptions made. The liner appeared to be saturated to a depth between 18 and 33 cm at the end of the first year of monitoring. Transit time calculations cannot be verified yet, since breakthrough has not occurred. The work conducted so far indicates that compacted soil barriers can be constructed to meet the saturated hydraulic conductivity requirement established by the U.S. EPA.     

Release Of Some Trace Elements From Sluiced Fly Ash On Acidic Soils With Particular Reference To Boron

The purpose of this study was to examine the relationship between the concentration of boron (B) and some other selected trace elements in soil solution as effected by hydrogen ion activity within the normal pH range for acidic soils commonly amended with agricultural limestone and, alternatively, alkaline fly ash. Sluiced alkaline fly ash was applied to an acidic, clay textured soil at rates equivalent to 0, 42, 84, 125 and 167 tonne ha^-1 based on the soil lime requirement. After wheat was grown and harvested the soil-ash mixtures were maintained at field capacity moisture content for an additional 4 months before pore water samples were extracted by immiscible displacement. The total concentrations of Co, Cr, Fe, V and Zn in the ash treated soils increased by < 10% at the highest application rate of ash, the content of Cu was increased by 13% and B by 38%. Only the concentration of boron increased appreciably in the pore water extracts. Release of B from the ash was correlated with the solubility behaviour of Ca and Mg, and not with the dissolution of glass phases in the ash. Speciation and adsorption calculations for the extracts were carried out using the program MINTEQ. Common Ca, Mg and Na borate minerals were undersaturated with respect to the equilibrated solutions. Application of the constant capacitance model to the adsorption of B on mineral surfaces suggested that adsorption had little effect on total dissolved B at pH values below 6.0. Predicted concentrations of B in solutions, equilibrated with calcite in a subsurface horizon, were up to 10.6 mg dm^-3; more than double the recommended maximum concentration for B (5mg dm^-3) in potable water in Ontario.     

Utilization of sepiolite materials as a bottom liner material in solid waste landfills

Landfill bottom liners are generally constructed with natural clay soils due to their high strength and low hydraulic conductivity characteristics. However, in recent years it is increasingly difficult to find locally available clay soils that satisfy the required engineering properties. Fine grained soils such as sepiolite and zeolite may be used as alternative materials in the constructions of landfill bottom liners. A study was conducted to investigate the feasibility of using natural clay rich in kaolinite, sepiolite, zeolite, and their mixtures as a bottom liner material. Unconfined compression tests, swell tests, hydraulic conductivity tests, batch and column adsorption tests were performed on each type of soil and sepiolite–zeolite mixtures. The results of the current study indicate that sepiolite is the dominant material that affects both the geomechanical and geoenvironmental properties of these alternative liners. An increase in sepiolite content in the sepiolite–zeolite mixtures increased the strength, swelling potential and metal adsorption capacities of the soil mixtures. Moreover, hydraulic conductivity of the mixtures decreased significantly with the addition of sepiolite. The utilization of sepiolite–zeolite materials as a bottom liner material allowed for thinner liners with some reduction in construction costs compared to use of a kaolinite-rich clay.     

Physical Determinants of Methane Oxidation Capacity in a Temperate Soil

Methane oxidation capacity of soil from an experimentalsite in Northwest England was strongly dependent on temperatureand percentage water holding capacity. The soil had a distincttemperature optimum of 25 °C, with capacity for net methaneoxidation being completely lost below 5 and greater than37 °C. Optimum percentage water holding capacity for methaneoxidation was in the range 30–60%, with significant reductions inmethane oxidation rates in soils outside this range. Organic andmineral layers within the soil showed differences in potentialmethane oxidation rate, with methane oxidation being most rapid inthe buried organic layer and least rapid in the surface organiclayer. The importance of soil structure and gas diffusionlimitation is underlined, as is the strong temperature dependenceof methane oxidation when such diffusion limitation is removed.     

Long-term Performance of a Permeable Reactive Barrier in Acid Sulphate Soil Terrain

Deep drainage technique utilised for flood mitigation in low-land coastal areas of Australia during the late 1960s has resulted in the generation of sulphuric acid in soil by the oxidation of pyritic materials. Further degradation of the subsurface environment with widespread contamination of the underlying soil and groundwater presents a major and challenging environmental issue in acid sulphate soil (ASS) terrains. Although several ASS remediation techniques recently implemented in the floodplain of Southeast Australia including operation of gates, tidal buffering and lime injections could significantly control the pyrite oxidation, they could not improve the long-term water quality. More recently, permeable reactive barriers (PRBs) filled with waste concrete aggregates have received considerable attention as an innovative, cost-effective technology for passive in situ clean up of groundwater contamination. However, long-term efficiency of these PRBs for treating acidic groundwater has not been established. This study analyses and evaluates the performance of a field PRB for treating the acidic water over 2.5 years. The pilot-scale alkaline PRB consisting of recycled concrete was installed in October 2006 at a farm of southeast New South Wales for treating ASS-impacted groundwater. Monitoring data of groundwater quality over a 30 month period were assessed to evaluate the long-term performance of the PRB. Higher pH value (~pH 7) of the groundwater immediately downstream of the PRB and higher rates of iron (Fe) and aluminium (Al) removal efficiency (>95%) over this study period indicates that recycled concrete could successfully treat acidic groundwater. However, the overall pH neutralising capacity of the materials within the barrier declined with time from an initial pH 10.2 to pH 7.3. The decline in the performance with time was possibly due to the armouring of the reactive material surface by the mineral precipitates in the form of iron and aluminium hydroxides and oxyhydroxides as indicated by geochemical modelling.