Search

In this pilot-scale constructed wetland (CW) study for treating groundwater contaminated with benzene, MTBE, and ammonia-N, the performance of two types of CWs (a wetland with gravel matrix and a plant root mat) was investigated. Hypothesized stimulative effects of filter material additives (charcoal, iron(III)) on pollutant removal were also tested. Increased contaminant loss was found during summer; the best treatment performance was achieved by the plant root mat. Concentration decrease in the planted gravel filter/plant root mat, respectively, amounted to 81/99% for benzene, 17/82% for MTBE, and 54/41% for ammonia-N at calculated inflow loads of 525/603 mg/m2/d, 97/112 mg/m2/d, and 1167/1342 mg/m2/d for benzene, MTBE, and ammonia-N. Filter additives did not improve contaminant depletion, although sorption processes were observed and elevated iron(II) formation indicated iron reduction. Bacterial and stable isotope analysis provided evidence for microbial benzene degradation in the CW, emphasizing the promising potential of this treatment technique.

Understanding the complex, interacting processes that determine the fate and transport of contaminants in groundwater is a major challenge for evaluating and predicting risks to clean water, human and ecological receptors and for designing effective remediation plans. Different physical and biogeochemical processes including advection, hydrodynamic dispersion, dissolution, sorption and biodegradation affect the migration of contaminants in saturated porous media like a groundwater system. In this chapter an overview of these processes is presented together with the basic theory on contaminant transport modeling, which represents an essential tool for a quantitative description of contaminant migration in the subsurface. Numerical simulations of typical contamination scenarios are presented, with the main goal of identifying the influence of different parameters on contaminant fate and transport such as transverse dispersivity, thickness and strength of the contamination source, recharge, biodegradation rates and mixing enhancement through flow focusing in high permeability zones. These numerical simulations are complemented by two examples, i.e. the reactive transport of toluene from a LNAPL source and a field study, where ammonium is continuously released from a leaking landfill to the underlying aquifer. The principal processes at the landfill site have been quantitatively integrated into the framework of a two-dimensional reactive transport model.

[1] The oxygen flux from the atmosphere into aquifers plays a key role for the biodegradation of organic solutes in groundwater and changing the water chemistry in general. In this paper, simple analytical solutions for the reactive transport of oxygen into groundwater are derived and compared to numerical models. The oxygen transfer is described analogous to diffusion into a semi-infinite domain with instantaneous reaction. We assume the capillary fringe does not exist and the concentration of oxygen is constant at the water table. Steady state analytical solutions are derived for the oxygen flux and for the concentration profiles of the reactants and products that could be volatile and nonvolatile. The simple approach is validated with numerical simulations. We can show that the analytical solutions agree very well with the numerical model. On the basis of this finding, simple analytical solutions can be used to calculate the depth of oxidation fronts in groundwater and the reactive transport of oxygen into groundwater.

Advanced Tools and Models to Improve River Basin Management in Europe in the Context of Climate Change - AquaTerra has developed from an integrated project of the 6th EU RTD Framework Programme that aims to provide the scientific basis for an improved river basin management through a better understanding of the river-sediment-soil-groundwater system as a whole, by integrating both natural and socio-economics aspects at different temporal and spatial scales. This book aims: The work illustrates the dynamic behavior of the pathway of pollutants in soils, groundwater, surface water and sediments. It highlights the fundamental importance of integrating knowledge from sereral combineddisciplines on various environmental compartments in order to understand the large number of processes that govern pollutant input, transport and turnover. Results shows that a significant step forward has been made in the development new analytical methods and of process-based numerical models that are capable of making predictions of likely trends and environmental changes to be expected in the near or distant future at the basin-scale. These models can be used e.g. to generate hydrologic scenarios based on climate models and to simulate pollutant distribution and turnover rates from decades to millennia. This title belongs to European Water Research Series . ISBN: 9781843393726 (Print) ISBN: 9781780401577 (eBook)

Oxygen transport across the capillary fringe is relevant for many biogeochemical processes. We present a non-invasive technique, based on optode technology, to measure high-resolution concentration profiles of oxygen across the unsaturated/saturated interface. By conducting a series of quasi two-dimensional flow-through laboratory experiments, we show that vertical hydrodynamic dispersion in the water-saturated part of the capillary fringe is the process limiting the mass transfer of oxygen. A number of experimental conditions were tested in order to investigate the influence of grain size and horizontal flow velocity on transverse vertical dispersion in the capillary fringe. In the same setup, analogous experiments were simultaneously carried out in the fully water-saturated zone, therefore allowing a direct comparison with oxygen transfer across the capillary fringe. The outcomes of the experiments under various conditions show that oxygen transport in the two zones of interest (i.e., the unsaturated/saturated interface and the saturated zone) is characterized by very similar transverse dispersion coefficients. An influence of the capillary fringe morphology on oxygen transport has not been observed. These results may be explained by the narrow grain size distribution used in the experiments, leading to a steep decline in water saturation at the unsaturated/saturated interface and to the absence of trapped gas in this transition zone. We also modeled flow (applying the van Genuchten and the Brooks-Corey relationships) and two-dimensional transport across the capillary fringe, obtaining simulated profiles of equivalent aqueous oxygen concentration that were in good agreement with the observations.

In this contribution we give a first general overview of results of recent studies in Germany which focused on contaminant leaching from various materials and reactive solute transport in the unsaturated soil zone to identify the key factors for groundwater risk assessment. Based on these results we developed new and improved existing methods for groundwater risk assessment which are used to derive a new regulatory concept for the upcoming "Decree for the Requirements of the Use of Alternative Mineral Building Materials in Technical Constructions and for the Amendment of the Federal Soil Protection and Contaminated Sites Ordinance" of the German Federal Ministry of Environment. The new concept aims at a holistic and scientifically sound assessment of the use of mineral recycling materials (e.g., mineral waste, excavated soils, slag and ashes, recycling products, etc.) in technical constructions (e.g., road dams) and permanent applications (e.g., backfilling and landscaping) which is based on a mechanistic understanding of leaching and transport processes. Fundamental for risk assessment are leaching standards for the mineral recycling materials. For each application of mineral recycling materials specific maximum concentrations of a substance in the seepage water at the bottom of an application were calculated. Technical boundary conditions and policy conventions derived from the "German precautionary groundwater and soil protection policy" were accounted to prevent adverse environmental effects on the media soil and groundwater. This includes the concentration decline of highly soluble substances (e.g., chloride and sulphate), retardation or attenuation of solutes, accumulation of contaminants in sub-soils and the hydraulic properties of recycling materials used for specific applications. To decide whether the use of a mineral recycling material is possible in a specific application, the leaching qualities were evaluated based on column percolation tests with various samples and compared with application-specific maximum concentrations. In the upcoming federal decree this simplified concept is realized using detailed tables which classify the leaching quality of mineral recycling materials and demonstrate potential application. A quality assurance system will be mandatory which defines specific testing programs (material properties and limit concentrations to be tested, number and schedule of testing) for the different mineral recycling materials using standardized methods (column percolation test).

Die molekulare Diffusion von Schadstoffen kann sowohl im Sand- und Kieskornbereich als auch bei Ton- oder Schlufflinsen als limitierender Faktor bei der Dekontamination von Boden- und Grundwasserverunreinigungen auftreten und so die in der Praxis haufig beobachteten langen Sanierungszeiten verursachen. Die Zeit, einen bestimmten Dekontaminationsgrad zu erreichen, nimmt dabei quadratisch mit der Diffusionsstrecke (Korn-, Aggregatradius bzw. Schichtmachtigkeit) und linear mit abnehmendem Diffusionskoeffizienten zu. Bereits bei einer feinporosen Sand- und Kiesfraktion kann die Zeit, um die Schadstoffgehalte um 90% zu reduzieren, deutlich uber der mittleren Verweilzeit bei nasmechanischen Bodenreinigungsverfahren liegen. Bei Schadstoffen, die stark sorbiert werden, konnen Desorptionszeiten im Bereich von mehreren Jahrzehnten erreicht werden. Noch langere Zeiten tretenin situ bei bindigem Material (z. B. Tonlinsen) aufgrund der langen Diffusionsstrecken auf. Bei der diffusionsbedingten langsamen Abnahme der Schadstoffgehalte treten entsprechend geringe Schadstoff-Frachten auf, was bei der Sanierung von Bodenverunreinigungen und bei der Bewertung einer von kontaminiertem Erdreich ausgechenden Grundwassergefahrdung berucksichtigt werden konnte.

Mass transfer, mixing, and therefore reaction rates during transport of solutes in porous media strongly depend on dispersion and diffusion. In particular, transverse mixing is a significant mechanism controlling natural attenuation of contaminant plumes in groundwater. The aim of the present study is to gain a deeper understanding of vertical transverse dispersive mixing of reaction partners in saturated porous media. Multitracer laboratory experiments in a quasi two-dimensional tank filled with glass beads were conducted and transverse dispersion coefficients were determined from high-resolution vertical concentration profiles. We investigated the behavior of conservative tracers (i.e., fluorescein, dissolved oxygen, and bromide), with different aqueous diffusion coefficients, in a range of grain-related Peclet numbers between 1 and 562. The experimental results do not agree with the classical linear parametric model of hydrodynamic dispersion, in which the transverse component is approximated as the sum of pore diffusion and a compound-independent mechanical dispersion term. The outcome of the multitracer experiments clearly indicates a nonlinear relation between the dispersion coefficient and the average linear velocity. More importantly, we show that transverse mechanical dispersion depends on the diffusion coefficient of the compound, at least at the experimental bench-scale. This result has to be considered in reactive-transport models, because the typical assumption that two reactants with different aqueous diffusive properties are characterized by the same dispersive behavior does not hold anymore.

Transport and natural attenuation of contaminant plumes in groundwater are often controlled by transverse dispersion. The extent of mixing between dissolved reaction partners at the fringe of a plume determines its length and depends strongly on the groundwater flow field. Transient flow conditions as well as the focusing of the flow in high-permeability zones may enhance transverse mixing of dissolved species and, therefore, create favorable conditions for the natural attenuation of contaminant plumes. The aim of the present study is to experimentally test the influence of these processes on solute mixing and to directly compare the results with those under analogous homogeneous and steady-state conditions. We have performed conservative and reactive tracer experiments in a quasi two-dimensional tank filled with glass beads of different sizes. The experiments have been carried out in both homogeneous and heterogeneous porous media under steady-state and transient (i.e. oscillating) flow fields. We used fluorescein as conservative tracer; whereas an alkaline solution (NaOH) was injected into ambient acidic water (HCl) in the reactive experiments. A pH indicator was added to the reacting solutions in order to visualize the emerging plume. We simulated the laboratory experiments with a numerical model and compared the outcomes of the model with the measured concentrations at the outlet of the tank and with the observed tracer plumes. Spatial moments, a newly defined flux-related dilution index, the product mass fluxes and the reaction enhancement factors were calculated to quantify the differences in mixing and reaction extent under various experimental conditions. The results show that flow focusing in heterogeneous porous media significantly enhances transverse mixing and mixing-controlled reactions, whereas temporally changing flow fields appear to be of minor importance.

AquaTerra is one of the first environmental projects within the 6th Framework program by the European Commission. It began in June 2004 with a multidisciplinary team of 45 partner organizations from 13 EU countries, Switzerland, Serbia, Romania and Montenegro. Results from sampling and modeling in 4 large river basins (Ebro, Danube, Elbe and Meuse) and one catchment of the Brévilles Spring in France led to new evaluations of diffuse and hotspot input of persistent organic and metal pollutants including dynamics of pesticides and polycyclic aromatic hydrocarbons, as well as metal turnover and accumulation. While degradation of selected organic compounds could be demonstrated under controlled conditions in the laboratory, turnover of most persistent pollutants in the field seems to range from decades to centuries. First investigations of long-term cumulative and degradation effects, particularly in the context of climate change, have shown that it is also necessary to consider the predictions of more than one climate model when trying to assess future impacts. This is largely controlled by uncertainties in climate model responses. It is becoming evident, however, that changes to the climate will have important impacts on the diffusion and degradation of pollutants in space and time that are just at the start of their exploration. © 2008 INRA EDP Sciences.

Soot has been considered as a potentially important sorbent for organic contaminants in soils, sediments, and aerosols. This paper demonstrates that native (authigenic) extractable organic material (EOM) and surface-covering water on soot may have a substantial influence on sorption properties of the soot. Sorption isotherms were determined for apolar and weakly polar sorbates (n-octane, cyclooctane, n-propylbenzene, naphthalene) from an aqueous solution to a standard reference material of diesel soot (SRM 2975) in the original state and after extraction with methanol. For all sorbates tested, removal of EOM from soot by methanol caused the sorption isotherms to be more nonlinear (decrease of Freundlich exponents by 0.19-0.25) compared to the untreated soot. The changes in the isotherms depend on both sorbate structure and sorbate concentration and can be accounted for by two opposing roles that EOM could have on the sorption properties of soot (i) enhancing the overall sorption by absorbing the sorbate into the EOM phase, and (ii) attenuating the sorbate adsorption to the soot carbon surface through sorption competition or site blockage. The n-alkane-to-cycloalkane sorption coefficient ratios (Kn/Kc) indicated that the removal of EOM altered the sorption mode for alkanes from absorption to adsorption. A comparison of the sorption isotherms measured in aqueous suspensions with the soot-air sorption coefficients reported for SRM 2975 in the literature showed that sorption to "soot in water" is significantly weaker than sorption to "soot in air", indicating that complete surface coverage with water suppresses the sorption by soot.

Preface. Laurent Charlet: Editor of the Journal of Hydrology.; International audience; If pollutants would always remain in the compartments they were deposited in, a lot of environmentalists would have to worry a lot less about. Most environmental pressures, however, develop a dynamic behavior and numerous processes govern the pathway of pollutants in the environment. They range from complex input functions into soils and surface water to migration processes in soil, groundwater, surface water and sediments to redistribution processes from soil and water into the atmosphere. Most environmental research aims to understand, parameterize, and model these processes that may be of chemical, biological, and physical nature. For this work, various spatial scales need to be considered. These range from pore size studies to basin-wide investigations whereas time scales of pollutant mobility range from hours to centuries and in some cases thousands of years. In addition, input and spreading behavior of environmental pollutants is often diffuse rather than clearly defined in time and space. Such spreading of input behavior means that it is often difficult to attribute sources and directions of pollutant transport and their turnover. This challenge is met by geoscientists, chemists, microbiologists, modelers and other environmental specialists in several manners.

Coal tar aged in a large-scale, artificial aquifer experiment for five years was subsequently investigated for leaching behavior of polycyclic aromatic hydrocarbons (PAHs). After five years, the initially liquid coal tar had solidified and formed segregated particles with a grain size similar to that of the sandy aquifer material. The composition of the aged coal tar (ACT) with regard to PAHs was remarkably different from that of the original bulk coal tar (BCT), because most of the low-molecular-weight compounds had been depleted. Equilibrium aqueous-phase concentrations of 17 PAHs leaching from the aquifer material containing the ACT were measured from consecutive equilibration steps at increasing temperatures of between 25 and 100 degrees C using accelerated solvent extraction. The results showed 2- to 5,000-fold lower concentrations than those from BCT, indicating dramatic changes of dissolution behavior of PAHs from coal tar after the five-year aging period. Predictions based on Raoult's law with the subcooled liquid solubilities substantially overestimated the equilibrium aqueous-phase concentrations of the PAHs from ACT, whereas the estimations were reasonable if the solid solubilities were employed instead. The enthalpies of phase transfer from ACT to water were determined based on the van't Hoff equation. The resulting values agreed with the dissolution enthalpies of pure solid rather than subcooled liquid PAHs.

This study reports sorption isotherms of the endocrine disruptors nonylphenol (NP) and octylphenol (OP) in three sediment samples from the Ebro River basin (NE Spain), with organic carbon fractions (f(OC)) ranging from 0.0035 to 0.082 g(OC)g(-1). All isotherms were fitted to the Freundlich model with slightly nonlinear exponents ranging from 0.80 to 0.94. The solubility of the compounds as well as the organic carbon (OC) content had the strongest influences on the sorption behavior of these compounds. Comparison of the laboratory-spiked samples with the native contamination of NP of 45 water and concurrent sediment samples resulted in reasonable matches between both data sets, even though the lowest concentrations in the field were not completely reached in laboratory tests. This good agreement indicates that sorption laboratory data can be extrapolated to environmental levels and therefore the distribution of nonylphenol between sediments and water can be predicted with a precision of one order of magnitude. Furthermore, laboratory experiments with simultaneous loading of NP and OP revealed negligible competition for sorption sites at low concentrations.

The identification and characterization of carbonaceous materials (CMs) that control hydrophobic organic chemical (HOC) sorption is essential to predict the fate and transport of HOCs in soils and sediments. The objectives of this paper are to determine the types of CMs that control HOC sorption in the oxidized and reduced zones of a glacially deposited groundwater sediment in central Illinois, with a special emphasis on the roles of kerogen and black carbon. After collection, the sediments were treated to obtain fractions of the sediment samples enriched in different types of CMs (e.g., humic acid, kerogen, black carbon), and selected fractions were subject to quantitative petrographic analysis. The original sediments and their enrichment fractions were evaluated for their ability to sorb trichloroethene (TCE), a common groundwater pollutant. Isotherm results and mass fractions of CM enrichments were used to calculate sorption contributions of different CMs. The results indicate that CMs in the heavy fractions dominate sorption because of their greater mass. Black carbon mass fractions of total CMs in the reduced sediments were calculated and used to estimate the sorption contribution of these materials. Results indicate that in the reduced sediments, black carbon may sequester as much as 32% of the sorbed TCE mass, butthat kerogen and humin are the dominant sorption environments. Organic carbon normalized sorption coefficients (K(oc)) were compared to literature values. Values for the central Illinois sediments are relatively large and in the range of values determined for materials high in kerogen and humin. This work demonstrates the advantage of using both sequential chemical treatment and petrographic analysis to analyze the sorption contributions of different CMs in natural soils and sediments, and the importance of sorption to natural geopolymers in groundwater sediments not impacted by anthropogenic sources of black carbon.

A series of integral pumping tests (IPTs) has been conducted at a former gasworks site to quantify the contaminant mass flow rates and average concentration in groundwater along three control planes across the groundwater flow direction. The measured concentration-time series were analysed numerically with the help of the inversion code CSTREAM and a flow and transport model representing the highly heterogeneous aquifer. Since the control planes cover the entire downstream width of the potentially contaminated area, they allow conclusions to be drawn about the current location and spread of the contaminant plume. Previous evaluations of integral pumping tests could calculate three scenarios concerning the spread of the plume around the IPT well: (i) the plume is located to the right of the pumping well, (ii) to the left, or (iii) is distributed symmetrically around it. To create a more realistic picture of the plume position, a series of direct-push monitoring wells were installed along one control plane. The concentrations found in these wells were included in the numerical analysis to condition the numerical inversion results, and allowed the identification of a more pronounced plume centre and fringe, which supports the development of optimised remediation strategies.

In case of dissolved electron donors and acceptors, natural attenuation of organic contaminant plumes in aquifers is governed by hydrodynamic mixing and microbial activity. Main objectives of this work were (i) to determine whether aerobic and anaerobic biodegradation in porous sediments is controlled by transverse dispersion, (ii) to elucidate the effect of sediment heterogeneity on mixing and biodegradation, and (iii) to search for degradation-limiting factors. Comparative experiments were conducted in two-dimensional sediment microcosms. Aerobic toluene and later ethylbenzene degradation by Pseudomonas putida strain F1 was initially followed in a plume developing from oxic to anoxic conditions and later under steady-state mixing-controlled conditions. Competitive anaerobic degradation was then initiated by introduction of the denitrifying strain Aromatoleum aromaticum EbN1. In homogeneous sand, aerobic toluene degradation was clearly controlled by dispersive mixing. Similarly, under denitrifying conditions, microbial activity was located at the plume's fringes. Sediment heterogeneity caused flow focusing and improved the mixing of reactants. Independent from the electron accepting process, net biodegradation was always higher in the heterogeneous setting with a calculated efficiency plus of 23-100% as compared to the homogeneous setup. Flow and reactive transport model simulations were performed in order to interpret and evaluate the experimental results.

For predicting organic carbon–water partitioning of organic pollutants in soils and sediments, a simple empirical relationship is derived from Raoult's law and fitted to data sets of experimental organic carbon normalized partition coefficients ( K oc ) and aqueous solubilities ( S i ) of 64 hydrophobic organic chemicals (HOCs) from literature including mono- and polycyclic aromatic hydrocarbons, halogenated monoaromatic and alkyl hydrocarbons, and polychlorinated biphenyls. Although over 5 orders of magnitude are covered in sorptivity (log K oc ), the new relationship (log K oc = − 0.85 log S i − 0.55) predicts K oc with an average absolute deviation of only 0.23 log units. The relationship between K oc and S i is inverse and slightly nonlinear. The product of K oc times S i (= K oc ∗ , which indicates the theoretical maximum contaminant loading at its solubility limit per unit mass of organic carbon) is 0.098 kg kg −1 and 0.012 kg kg −1 for compounds with water solubilities of 1 g L −1 and 1 μg L −1 , respectively.

Kurzfassung Auf dem Gelände eines ehemaligen Gaswerks (Testfeld Süd) wurden Immissionspumpversuche (IPVs) zur Quantifizierung der Fracht und der mittleren Konzentration gaswerkstypischer Schadstoffe entlang von drei Kontrollquerschnitten durchgeführt. Die daraus resultierenden Konzentrationsganglinien wurden mithilfe des Inversionsprogramms CSTREAM und eines Strömungs- und Transportmodells des hydraulisch extrem heterogenen Grundwasserleiters numerisch ausgewertet. Die den gesamten Abstrombereich der Verdachtsfläche erfassenden Kontrollquerschnitte ermöglichen Aussagen über die Position und Ausbreitung der Schadstofffahne auf dem Gelände des Testfeldes Süd. Bisherige Auswertungen von IPVs konnten die Verteilung der Schadstofffahne um den IPV-Brunnen für genau drei Fälle berechnen: entweder befindet sich die Fahne links vom Brunnen, rechts davon oder ist symmetrisch um ihn verteilt. Um eine realistischere Vorstellung von der Fahnenposition zu ermöglichen, wurden in dieser Studie zusätzlich Direct-Push-Messstellen entlang einer Kontrollebene installiert. Die in diesen Messstellen gemessenen Konzentrationen wurden zur Konditionierung der numerischen Inversionslösung herangezogen. Die Ergebnisse ermöglichen eine genauere Eingrenzung des Fahnenzentrums sowie des Fahnenrandes, was insbesondere die Erarbeitung angepasster und optimierter Sanierungsstrategien unterstützt., A series of integral pumping tests (IPTs) were conducted at a former gasworks site to quantify the contaminant mass flux and average concentration in groundwater along three control planes. The resulting concentration-time series were analysed numerically with the help of the inversion code CSTREAM and a flow and transport model representing the highly heterogeneous aquifer. Since the control planes cover the entire downstream width of the potentially contaminated area, they allow conclusions to be drawn about the current location and spread of the contaminant plume. Previous evaluations of integral pumping tests could calculate three scenarios concerning the spread of the plume around the IPT well: (i) the plume is located to the right of the well, (ii) to the left, or (iii) is distributed symmetrically around it. To create a more realistic picture of the plume position, a series of direct-push monitoring wells were installed along one control plane. The concentrations found in these wells were included in the numerical analysis to condition the inversion results, and resulted in a more pronounced plume centre and fringe, which supports the development of optimised remediation strategies.

Nonlinear sorption by natural organic matter may have a significant impact on the behavior of organic contaminants in soils and sediments. This study presents a molecular probe approach based on linear solvation energy relationships (LSERs) to identify and quantify the molecular interactions causing concentration-dependent sorption and proposes estimation methods for sorption nonlinearities. Sorption isotherms ranging over concentrations of more than 4 orders of magnitude were determined in batch systems for 23 and 16 chemically diverse probe compounds in a lignite sample and a peat soil, respectively. Each sorbent showed characteristic nonlinear sorption with Freundlich exponents (1/n) being 0.7-1. The LSER-based analysis revealed that the strength of nonspecific interactions did not vary with concentration for both sorbents. In lignite, specific interactions did not affect sorption nonlinearity either, suggesting that compound-independent factors of lignite were responsible for the nonlinear sorption. In the peat soil, by contrast, the specific interactions related to the solute polarizability/dipolarity parameter (S) decreased with increasing concentration. Consequently, compounds of higher S values were more susceptible to nonlinear sorption in the peat soil. Phenol probes have shown that hydrogen bond donating properties of sorbate compounds have a substantial impact on the overall strength of sorption with organic matter, but no significant influence on sorption nonlinearity. Heterocyclic aromatic compounds appear to undergo additional interactions that are not accounted for by the LSER. These additional interactions considerably enhance both sorption capacity and nonlinearity.

Sorption of nonionic compounds is strongly dependent on the content as well as the nature of the organic matter in soils and sediments. The composition and the structure of organic matter varies due to its origin and geological history and strongly influences the sorption affinity for nonionic organic compounds. Organic matter in unweathered shales and high-grade coals shows enhanced sorption (> 1 order of magnitude) compared to organic matter in recent soils or geologically young material and low-grade coals. The results obtained indicate a decrease in sorption with increasing proportions of oxygen-containing functional groups in natural organic substances. A first approximation to estimate sorption coefficients for various organic matter is provided by an empirical correlation between the hydrogen/oxygen (H/O) atomic ratio as an index of the oxidation of the organic matter and the organic carbon normalized sorption coefficients (K{sub OC}). This approximation also permits adjustment of K{sub OC} values derived from K{sub OW} data.

In this study, contaminant leaching from three different secondary materials (demolition waste, municipal solid waste incineration ash, and blast furnace slag) to groundwater is assessed by numerical modeling. Reactive transport simulations for a noise protection dam and a road dam (a typical German autobahn), in which secondary materials are reused as base layers, were performed to predict the breakthrough of a conservative tracer (i.e., a salt) and sorbing contaminants (e.g., PAHs like naphthalene and phenanthrene or heavy metals) at the groundwater table. The dam constructions have a composite architecture with soil covers in inclined layers and distinct contrasts in the unsaturated hydraulic properties of the used materials. Capillary barrier effects result in strong spatial variabilities of flow and transport velocities. Contaminant breakthrough curves at the groundwater table show significant tailing due to slow sorption kinetics and a wide distribution of travel times. While conservative tracer breakthrough depends primarily on subsoil hydraulic properties, equilibrium distribution coefficients and sorption kinetics represent additional controlling factors for contaminant spreading. Hence, the three secondary materials show pronounced differences in the temporal development of leached contaminant concentrations with consequences for breakthrough times and peak concentrations at the groundwater table. Significant concentration reductions due to dispersion occur only if the source concentrations decrease significantly prior to the arrival of the contaminant at the groundwater table. Biodegradation causes significant reduction of breakthrough concentrations only if flow velocities are low.

A coal tar contaminated site was characterized using traditional and innovative investigation methods. A careful interpretation of hydrogeological and hydrogeochemical data allowed for the conceptualization of the heterogeneous coal tar distribution in the subsurface. Past and future contaminant release from the source zone was calculated using a modeling framework consisting of a three-dimensional steady-state groundwater flow model (MODFLOW) and two hydrogeochemical models (MIN3P). Computational time of long-term simulations was reduced by simplifying the coal tar composition using 3 composite and 2 individual constituents and sequential application of a 2D centerline model (for calibration and predictions) and a 3D model (only for predictions). Predictions were carried out for a period of 1000 years. The results reveal that contaminant mass flux is governed by the geometry of zones containing residual coal tar, amount of coal tar, its composition and the physicochemical properties of the constituents. The long-term predictions made using the 2D model show that even after 1000 years, source depletion will be small with respect to phenanthrene, 89% of initial mass will be still available, and for the moderately and sparingly soluble composite constituents, 60% and 98%, respectively.

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic organic pollutants that are ubiquitously distributed in the environment at relatively high concentrations. In our study we investigated the long-term fate of atmospheric PAHs in soils of rural areas, resulting from diffuse pollution based on mass balances at the catchment scale. By determining PAHs in several environmental compartments, estimates of soil storages and water fluxes were made and compared with atmospheric deposition. The results indicate that more than 90% of the incoming PAHs remain in the catchments and accumulate in the topsoils. Furthermore, revolatilization of PAHs from soils and degradation in the soils is very limited, resulting in ongoing accumulation in topsoils, in particular for low-volatile PAHs. Combustion-derived carbonaceous particles were detected in atmospheric deposition as well as in the soil samples. Since these particles are very strong adsorbents, they are suspected to play a key role in the environmental fate of the diffuse distributed PAHs.

All over Europe there are numerous contaminated sites where top layers of soil or other materials are contaminated. Remediation of all these sites would be economically impossible and therefore site prioritisation is needed based on an evaluation of the risk to subsoil and groundwater contamination....

Publisher Summary This chapter provides details on the functioning of ceramic dosimeter sampling devices with particular focus on the role of the ceramic membrane and requirements regarding the solid receiving phase. A number of practical considerations are discussed to highlight strengths and limitations of ceramic dosimeters in the field. The ceramic dosimeter consists of a ceramic tube with a diameter of 1 cm and a wall thickness of 1.5mm. The pore size of the inner wall coating of the tube is 5 nm. The length of the tube can be varied, but in most applications so far, a length of 5 cm was used. The tube is filled with water-saturated sorbent and closed at either end with caps made of polytetrafluoroethylene. The ceramic membrane serves both as a diffusion barrier and as a container to hold the sorbent material. Key characteristics of this membrane with regard to quantitative time-integrated passive sampling are its porosity and inertness, its inner pore size, and its thickness. Upon diffusion of solutes through the ceramic membrane, they need to be trapped onto a receiving phase. The role of this is to maintain a steep concentration gradient between the exterior and the interior of the sampler in order to ensure continuous diffusion along the gradient into the sampling device. To allow for chemical analysis after sampling, they are required to yield high recovery rates of the target chemicals by means of solvent extraction or, potentially, thermo-desorption. Three different bead materials have been identified to fulfill these criteria. These are Amberlite IRA-743; Biosilon; and chlorinated hydrocarbons.

Concentrations and isotope compositions of polycyclic aromatic hydrocarbons (PAHs) were determined in natural soils of Southern Germany. In selected profiles perylene concentrations increased with soil depth when compared to the other PAH compounds present. However, its low solubility made vertical transport by seepage water unlikely. Therefore two mechanisms are discussed that could have caused the unusual distribution of perylene in these soils: (a) Atmospheric deposition of combustion-derived (i.e. pyrogenic) perylene in the top-soil and (b) in situ generation in the sub-soil of these specific terrestrial environments. This could have been caused by microbial activities or other catalytic processes yet unknown. In order to distinguish between pyrogenic and natural generation compound-specific 13 C/ 12 C ratios ( δ 13 C) were compared between perylene and other PAHs in samples from the top-soil and sub-soil. Despite successful clean-up of the extracts, low perylene concentrations and peak overlaps with benzo( e )pyrene and benzo( a )pyrene prevented determination of a unique δ 13 C value for perylene in the upper horizon. However, the δ 13 C value of perylene in the sub-soil was 5.7 permille more negative than other equal-mass PAHs (with m / z of 252) in the top-soil, which rather supports in situ generation of perylene in the sub-soil.

Diffusive–dispersive mass transfer is important for many groundwater quality problems as it drives the interaction between different reactants, thus influencing a wide variety of biogeochemical processes. In this study, we performed laboratory experiments to quantify O2 transport in porous media, across the unsaturated–saturated interface, under both conservative and reactive transport conditions. As reactive system we considered the abiotic oxidation of Fe2+ in the presence of O2. We studied the reaction kinetics in batch experiments and its coupling with diffusive and dispersive transport processes by means of one-dimensional columns and two-dimensional flow-through experiments, respectively. A noninvasive optode technique was used to track O2 transport into the initially anoxic porous medium at highly resolved spatial and temporal scales. The results show significant differences in the propagation of the conservative and reactive O2 fronts. Under reactive conditions, O2, continuously provided from the atmosphere, was considerably retarded due to the interaction with dissolved Fe(II), initially present in the anoxic groundwater. The reaction between dissolved O2 and Fe2+ led to the formation of an Fe(III) precipitation zone in the experiments. Reactive transport modeling based on a kinetic PHREEQC module tested in controlled batch experiments allowed a quantitative interpretation of the experimental results in both one- and two-dimensional setups.

Laboratory-scale flow-through experiments in a sand-filled chamber were performed to investigate the impact of aerobically growing Escherichia coli HB101-K12 on oxygen transfer across the capillary fringe (CF) to oxygen-depleted groundwater. In the experiments, both the effects of different nutrient concentrations and transient flow conditions were tested. The results of biotic experiments under oligotrophic and eutrophic conditions (6.8 g organic C L −1 ) were compared with those of an abiotic experiment. Moreover, in each experiment steady-state and transient conditions were considered, the latter induced by changing the water-table height. Growth of E. coli was quantified by cell counting in effluent samples and could be monitored due to intracellular production of the green fluorescent protein (GFP). Under eutrophic conditions, highest cell densities and strongest cell attachment were observed in the transition region of the CF. In this region, intensive bacterial respiration decreased oxygen concentrations relatively quickly, causing a steep oxygen gradient that resulted in a higher oxygen flux across the unsaturated–saturated interface. Under oligotrophic conditions, this effect was considerably reduced, but was still detectable. Due to oxygen supply from entrapped air, bacterial growth was slightly enhanced within the upper, newly formed CF region, directly after raising the water table. After lowering the water table to the initial height only a minor microbial impact on oxygen transfer was noticed, even under eutrophic conditions, because of the fast diffusion of oxygen in the (partially) air-filled pore spaces. Bacteria that remained in the transition region of the CF grew to higher densities due to better oxygen supply.

[1] Transverse dispersion across adjacent streamlines can control the amount of mixing and reaction between one or more contaminants and a limiting substrate along the fringes of groundwater plumes. Streamlines in groundwater converge and diverge in heterogeneous porous media, depending on the permeability distribution. When flow is focused in a high-permeability zone, the distance required for a solute to cross a given number of streamlines decreases, and the time allowed for mixing and reaction is reduced. Because the first effect outweighs the latter, the overall result is an enhancement of transverse mixing and reaction. Here we develop a conceptual model of heterogeneous two-dimensional structures facilitating flow focusing. We use the conceptual model to develop simple analytical expressions quantifying the extent to which mixing and reaction are enhanced when flow focusing occurs and compare these to results of numerical simulations. Significant enhancement of transverse mixing and reaction by flow focusing is observed; for the cases considered, flow focusing enhances the amount of reaction by a factor ranging from 1.8 to 11.9. The relatively simple analytical expressions demonstrate that the fraction of the domain height made up by high-permeability inclusions, the fraction of flow that passes through the inclusions, and the fringe bypassing of inclusions determine the amount of mixing and reaction enhancement for the permeability distributions considered. These results partially explain why field-scale dispersivities are larger than laboratory derived dispersivities, where homogeneous and isotropic sediments are typically used. Further work is needed to verify the theoretical results presented here with laboratory and field experiments and to expand the relatively simple analytical expressions to consider more heterogeneous three-dimensional permeability fields.

Naturlicher Abbau und Ruckhalt von Schadstoffen beruht im wesentlichen auf zwei Prozessen: 1) dem biologischen oder abiotischen Abbau von organischen Verbindungen und 2) der Wechselwirkung von Schadstoffen mit den festen Bodenbestandteilen, die in der Regel jedoch nur eine temporare Festlegung (Sorption/Desorption) und damit einen verlangsamten Transport im Untergrund bewirkt (Retardation). Dispersion fuhrt lediglich zur einer (lokal oft nur geringen) „Verdunnung“ der Schadstoffkonzentrationen bei ungeminderter Schadstoff-Fracht. Im folgenden werden die zum Verstandnis der reaktiven Transportprozesse wichtigen Grundlagen eingefuhrt. Dabei werden im wesentlichen organische Schadstoffe angesprochen — die dargestellten Modelle sind z.T. aber auch auf anorganische Stoffe anwendbar.

A PAH contaminated river floodplain soil was separated according to grain size and density. Coal and coal-derived particles from coal mining, coal industry and coal transportation activities were identified by organic petrographic analysis in our samples. Distinct concentrations of PAHs were found in different grain size and density fractions, however, similar distribution patterns of PAHs indicated similar sources. In addition, although light fractions had the mass fraction by weight of less than 5%, they contributed almost 75% of the total PAHs in the soil. PAH concentrations of all sub fractions showed positive correlation with their TOC contents. Altogether, coal and coal-derived particles that were abundant in light fractions could be the dominant geosorbents for PAHs in our samples.

The contents of nonhydrolyzable organic matter (NHC) and black carbon (BC) were measured in soils and sediments from the Pearl River Delta, South China. Polycyclic aromatic hydrocarbons (PAHs) were extracted respectively by Soxhlet and an accelerated solvent extraction device (ASE) using different solvents. In addition, sequential aqueous leaching at different temperatures was carried out. The PAH content extracted with the sequential three solvent ASE is two times higher than that using the Soxhlet extraction method. The relationship of the PAH content with the NHC content is very significant. The PAH concentrations measured at various temperature steps fit well to the Van't Hoff equation and the enthalpy was estimated. The investigation indicates that condensed organic matter such as kerogen carbon, aged organic matter, and BC is relevant for the extraction and distribution of native PAHs in the investigated field soils and sediments.

Assessing the potential of natural attenuation in groundwater relies on the ability to predict and quantify the processes that occur in contaminant plumes. Transverse dispersion is a significant mass transfer mechanism for mixing of electron acceptors and donors and thus may control the lengths of steady state plumes. Laboratory experiments were carried out using a 2-dimensional acrylic glass tank filled with glass beads, quartz sand and field site material as porous media. Flow velocities and grain sizes were varied in order to cover a large range of Peclet numbers including typical field scenarios. The laboratory study was extended by a comprehensive literature search to compare the new results with earlier work. As a result we propose a new empirical relationship for prediction of transverse dispersion coefficients (Dt) which is based on the Peclet number (Pe). This new relationship indicates a nonlinear dependency on the flow velocity (νa) and grain size (d), namely a relative decrease of the dispersion coefficient with increasing flow velocity in relatively fast flowing water: Dt / Daq = Dp / Daq + 0.28(Pe)0.72 (with Pe = νad / Daq; Daq and Dp denote the aqueous and pore diffusion coefficients, resp.).

The unsaturated zone including the capillary fringe is a very dynamic and active environment for biogeochemical processes. Modeling of fate and transport of organic pollutants has to account for vapor phase and sewage water transport coupled to the biogeochemical processes occurring. This study presents results from numerical simulations validated with data of a well-controlled field experiment on volatilization of a multi-component organic mixture in the unsaturated zone. Sensitivity analyses show that the overall biodegradation rates depend mainly on properties of the organic pollutants such as Henry’s Law constant, the soil water content, and on the individual degradation rate constants or temperature. Low Henry’s law constants result in relatively high biodegradation rates whereas compounds with high vapor pressure und low water solubility are lost to the atmosphere. The contaminant transfer rates into groundwater are relatively small, but lead locally to concentrations above the legal limit in the capillary fringe region. Contaminant transport by seepage water is just minor compared to diffusive vapor phase fluxes of volatile compounds.

A process-based modelling approach of organic contaminant spreading is presented, which allows to quantify the increase of groundwater pollution risk due to preferential flow and particle-facilitated transport in the vadose zone. Both effects are illustrated by means of a parameter study based on realistic input data. When coupled with biodegradation, preferential flow and particle-facilitated transport lead to an increase in the long-term concentration to be expected at the groundwater table as both processes reduce the bioavailability of the contaminant due to either shorter residence times (preferential flow) or lower accessibility (particle-facilitated transport). Model predictions account for the amount and the velocity of preferential flow as well as the potentially kinetic interaction between organic contaminant and mobile particles.

[1] The finite maximum length of a steady state contaminant plume is determined by developing and employing a new analytical solution which overcomes two drawbacks associated with existing approaches. First, we account for a sharp front caused by the complete consumption of the pollutant (“electron donor”) and some electron acceptor in an instantaneous binary reaction occurring at the front. This approach is not based on purely conservative or first-order degradation models which lead to theoretically infinite plumes and, in addition, depend on a concentration threshold. Second, a vertical aquifer cross section with finite thickness is selected as a model in order to better represent the supply of electron acceptors mostly entering the aquifer from the top. This type of setting allows investigation of the impact of aquifer thickness on plume length. An implicit representation of the donor-acceptor front in a finite vertical domain previously required numerical solutions of the underlying advection-dispersion-reaction equation; we provide for the first time an analytical solution of this two-dimensional transport problem. The length of the plume is found to be given by the point of intersection of the donor-acceptor front and the aquifer bottom. Furthermore, a rather simple and highly accurate approximation is derived to compute the steady state plume length. A comprehensive sensitivity analysis reveals that results are most strongly influenced by aquifer thickness, followed by vertical transverse dispersivity and, to a somewhat lesser extent, by chemical reaction parameters. Longitudinal dispersivity has practically no effect on plume length, and furthermore, there is zero impact of linear velocity. With regard to groundwater risk assessment at the field scale it is also important to note that the present approach is meant to provide an upper bound on the actual plume length. Further research activities may be directed to refine the transport model by considering, for instance, degradation inside the plume and the limited vertical extent of the contaminant source.

The contamination of soils and sediments by carbonaceous particles has been investigated by organic-petrological methods. Results from the study of soils from industrialised areas show that airborne contaminants like brown coal, hard coal, charcoal, and char have accumulated. The observed soil contamination is due to dust emission by open-cast brown coal mines, to the burning of brown coal and hard coal, and coking plants. It was found that soil contamination can occur over a distance of several dozen km from the contamination sources. The investigation of soils and sediments demonstrates the heterogeneous character of organic matter and proves the presence of coal and charcoal particles of fossil origin in the majority of the samples. The heterogeneity of the organic matter is found responsible for variations in the sorption behaviour of organic pollutants like polycyclic aromatic hydrocarbons in soils and sediments.

Desorption experiments were carried out in flow through columns following long-term sorption batch experiments (up to 1010 days at 20 degrees C; Rugner, H.; Kleineidam, S.; Grathwohl, P. Long-term sorption kinetics of phenanthrene in aquifer materials. Environ. Sci. Technol. 1999, 33, 1645-1651) to elucidate sorption/desorption hysteresis phenomena of phenanthrene in aquifer materials. Most of the sorbents employed in this study (homogeneous lithocomponents separated from aquifer sediments or fresh rock fragments) showed highly nonlinear sorption isotherms because of coal particles embedded inside the grains. Because sorption capacities were high, sorption equilibrium was not reached in most of the sorbents during the initial sorptive uptake experiments lasting up to 1010 days. Desorption was studied up to 90 days at 20 degrees C. The temperature was raised after that stepwise from originally 20 to 30, 40, 50, and finally to 70 degrees C for selected samples to estimate activation energies of desorption. A numerical intraparticle pore diffusion model was used to fit sorptive uptake data and subsequently for pure forward prediction of the release rates in the desorption column experiments. Desorption was initially fast followed by extended tailing which in other studies is fitted by using multirate first-order models. Our results demonstrate that the retarded intraparticle pore diffusion model can predict the desorption rates with a single diffusion rate constant obtained independently from the long-term batch sorption experiment. No evidence for hysteresis was found, suggesting that many hysteresis phenomena reported earlier are experimental artifacts resulting from nonequilibrium effects and "nonphysical" models. The different temperature steps allowed one to additionally calculate activation energies of desorption (45-59 kJ mol(-1)), which were in reasonably good agreement with results from earlier studies for a retarded pore diffusion process. In addition, equilibrium sorption isotherms were determined at 20 and 40 degrees C to compare sorption and desorption enthalpies. Both were in good agreement, confirming that desorption was not significantly different from sorption.

Im Abstrom der „ehemaligen Abfalldeponie Osterhofen“ wurden Konzentrationen an Ammonium festgestellt, die deutlich uber dem in Baden-Wurttemberg geltenden Prufwert liegen. Im Rahmen detaillierter Natural Attenuation (NA) Untersuchungen wurde uberpruft, inwieweit die Nutzung mikrobiologischer Abbau- und Ruckhalteprozesse des Ammoniums eine geeignete Entscheidungsoption fur den Standort darstellt. Das Ergebnis der hierbei im Wesentlichen durchgefuhrten Frachtbestimmungen (mittels Immissionspumpversuchen) sowie einer konzeptionellen numerischen Modellierung des Ammoniumabbaues am Standort war, dass ein mikrobiologischer Abbau des Ammoniums zu Nitrat stattfindet (70–85 % Abbau innerhalb einer Distanz von ca. 450 m), dass allerdings aufgrund der diffusiv-/dispersiv bedingten langsamen Zufuhr von Sauerstoff in die Abstromfahne ein insgesamt ca. 550–680 m langer, stationarer Reaktionsraum existiert. Eine Gefahr fur das Grundwasser im weiteren Abstrom der Deponie konnte ausgeschlossen werden. Eine gezielte Uberwachung der NA-Prozesse kann am Standort an die Stelle einer aktiven Sanierungsmasnahme treten.

Bei der Uberwachung der aquatischen Umwelt spielt die Probennahme eine wichtige Rolle. Dabei konnen zwei Arten der Probennahme unterschieden werden. Bei der konventionellen Probennahme werden Proben aktiv , z. B. durch Schopfen oder Pumpen gewonnen. Demgegenuber steht die passive Probennahme, bei der Substanzen entsprechend ihres Massentransfergradienten ohne eine aktive Handlung vom Probennahmegerat aufgenommen werden. Trotz der Entwicklung zahlreicher passiver Probennehmer ist ihr Einsatz im Wasser bis heute weitestgehend auf den Forschungsbereich beschrankt. Leicht verfugbare und besser verbreitete Informationen bezuglich der Passivsammler im Allgemeinen, und ihrer vielseitigen Anwendungsmoglichkeiten im Speziellen, konnen helfen gegenwartigen Beschrankungen im Einsatz von Passivsammlern entgegen zu wirken. Welche Passivsammlersysteme gibt es, welche sind bereits kommerziell verfugbar und im Feld gepruft? Wie sind die Sammler aufgebaut und wo liegen die Vorzuge und Schwachen im Vergleich zur aktiven Probennahme? Dieser Artikel gibt einen Uberblick uber den gegenwartigen Stand der Entwicklungen und soll bei der Entscheidungsfindung fur oder wider einen Passivsammlereinsatz unter Feldbedingungen helfen.

[1] Preferential solute transport coupled with diffusion into the surrounding matrix region has been examined in a silty loam soil by conducting macropore column experiments for various hydrophobic organic compounds (phenanthrene, 1, 2-DCB, TCE, carbofuran) representing the polycyclic aromatic hydrocarbons, chlorobenzenes, chlorinated solvents, and pesticides. A new and ready-to-use analytical solution was developed for this setting to model the breakthrough curves. The model accounts for advection in the macropore region, diffusion into the matrix region, and linear sorption in both regions. In this setting, hydrodynamic dispersion is negligible as proved by a comparison of an advection-dispersion model of finite pulse input. Conservative tracer experiments were predicted very well with independently determined transport parameters except for the tortuosity factor, which was used as a fitting parameter for the pore diffusion coefficient in the matrix. In case of sorbing solutes the sorption coefficient (Kd) was used as additional fitting parameter. The fitted Kd was 65% smaller for less sorbing compounds, e.g., carbofuran, and 80% less for strongly sorbing compounds, e.g., phenanthrene compared to the independently determined Kd from batch experiments. This indicates that sorption equilibrium was not obtained completely during the matrix diffusion at the timescale of the macropore flow experiment.

[1] In this study the impact of sorption/desorption kinetics between organic contaminants and mobile particles suspended in subsurface water is analyzed. TCE migration through a granular activated carbon column is investigated at different transport velocities with lignite and activated carbon particles as mobile carriers. The measured breakthrough characteristics of TCE can be reproduced by a reactive transport model simulating sorption/desorption kinetics applying an intraparticle diffusion approach for mobile particles and the packed bed of granular activated carbon. Model predictions are based on independently measured physicochemical parameters, i.e., no calibration of TCE sorption/desorption is required. The close matches of experimental data to predicted data validate the exclusively process-based model assumptions and indicate that this approach has large predictive capabilities. Extending these findings, a sensitivity study is presented in order to specify under which conditions sorption/desorption of contaminants in mobile particles has to be modeled as a kinetic process. It is found that sorption/ desorption kinetics are of major importance for Damkohler numbers between 0.01 and 100.

Groundwater contamination due to complex organic mixtures such as coal tar, creosote and fuels is a widespread problem in industrialized regions. Although most compounds in these mixtures are biodegradable, the contaminant sources are very persistent for many decades after the contamination occurred (e.g., more than 100 years ago at gasworks sites). This limited bioavailability is due to slow dissolution processes. This study presents results from a large scale tank experiment (8 m long) on the long-term (354 days) dissolution kinetics of BTEX and PAHs from a 2.5 m long coal tar pool and 0.5 m long (smear) zone containing coal tar blobs distributed in a coarse sand. The results inidicate (1) that Raoult's law holds for estimation of the saturation aqueous concentrations of the coal tar constituents, (2) that for the dissolution of smear zones longer than approximately 0.1 m and with more than 3-5% residual saturation, the local equilibrium assumption is valid and (3) that although very small (< 0.1 mm), the transverse vertical dispersivity dominates the pool dissolution processes. Typical time scales for removal of the pollutants from the blob zone and the pool are in the order of a few weeks to more than 10,000 years, respectively.

Equilibrium sorption isotherms were measured for five different low-polarity organic compounds (benzene, trichloroethene, 1,2- and 1,4-dichlorobenzene, and phenanthrene) over a wide concentration range. The investigated sorbents can be grouped into the following three classes: (1) humic soil organic matter, which shows linear sorption isotherms (solely partitioning, as observed in the peat sample); (2) carbon materials, which were thermally altered (due to their natural history or industrial production) and thus contain a high specific surface area and exhibit nonlinear isotherms, and (3) pure engineered microporous materials (e.g., zeolites and activated carbon), where adsorption is solely due to a pore-filling process. Sorption of all compounds was fitted very well by the Polanyi-Dubinin-Manes (PDM) model, which for sorbents containing humic organic matter (e.g., peat) was combined with linear partitioning. Both the partitioning and the Polanyi-Dubinin-Manes model predict unique sorption isotherms of similar compounds if the solubility-normalized aqueous concentration is used. In addition, an inverse linear relationship between the distribution coefficient (Kd) and water solubility, which was very well confirmed by the data, is obtained. This also leads to unit-equivalent Freundlich sorption isotherms and explains the often observed apparent correlation between sorption capacity at a given concentration (e.g., Freundlich coefficient) and sorption nonlinearity (Freundlich exponent).