Sulfat-dominierter BTEX-Abbau im Grundwasser eines ehemaligen Gaswerksstandortes

In the area of a former gas-works in Düsseldorf (Germany) a soil and groundwater contamination with up to 100 mg/l BTEX (benzene, toluene, ethylbenzene and xylenes) was investigated. Benzene is the dominant aromatic hydrocarbon in the groundwater. The investigations show a natural biodegradation of BTEX by oxygen, manganese oxides, nitrate, ferric hydroxide and sulfate in the sand and gravel aquifer. Sulfate reduction is the most important degradation process in the contamined groundwater. As a product of sulfate reducion, sufids were formed in the sediments of the aquifer. A balance of oxidants is presented as a tool to quantify BTEX degradation and to differ this from sorption and dilution processes. In the contaminated area the degradation of aromatic hydrocarbons leads to the release of carbon dioxide. The highest free CO ₂ -concentration was found in the region of the groundwater table. Outgassing of CO ₂ is important and was verified by deep-specific soil-gas sampling. The knowledge of these processes in the subsoil is a requirement for making predictions for in-situ remediation effects.     

Groundwater Pollution Arising from the Disposal of Creosote Waste

Creosote-contaminated groundwater contains a complex mixture of phenols, aromatic hydrocarbons and nitrogen-, sulphur- or oxygen-containing heterocyclic, aromatic compounds. One of the most important factors that limits the spreading of these contaminants in groundwater aquifers is degradation by subsurface micro-organisms.
This paper gives an overview of the present knowledge about microbial degradation of creosote contaminants under aerobic and anaerobic conditions. Furthermore, various techniques for biological remediation of creosote-contaminated groundwater are outlined. These techniques include enhancement of the native population of subsurface micro-organisms to degrade the contaminants ( in situ treatment) and withdrawal of the groundwater followed by treatment by various wastewater treatment processes (above-ground treatment).     

Intrinsic biodegradation potential of aromatic hydrocarbons in an alluvial aquifer--potentials and limits of signature metabolite analysis and two stable isotope-based techniques

Three independent techniques were used to assess the biodegradation of monoaromatic hydrocarbons and low-molecular weight polyaromatic hydrocarbons in the alluvial aquifer at the site of a former cokery (Flémalle, Belgium).Firstly, a stable carbon isotope-based field method allowed quantifying biodegradation of monoaromatic compounds in situ and confirmed the degradation of naphthalene. No evidence could be deduced from stable isotope shifts for the intrinsic biodegradation of larger molecules such as methylnaphthalenes or acenaphthene. Secondly, using signature metabolite analysis, various intermediates of the anaerobic degradation of (poly-) aromatic and heterocyclic compounds were identified. The discovery of a novel metabolite of acenaphthene in groundwater samples permitted deeper insights into the anaerobic biodegradation of almost persistent environmental contaminants. A third method, microcosm incubations with ¹³C-labeled compounds under in situ-like conditions, complemented techniques one and two by providing quantitative information on contaminant biodegradation independent of molecule size and sorption properties. Thanks to stable isotope labels, the sensitivity of this method was much higher compared to classical microcosm studies. The ¹³C-microcosm approach allowed the determination of first-order rate constants for ¹³C-labeled benzene, naphthalene, or acenaphthene even in cases when degradation activities were only small. The plausibility of the third method was checked by comparing ¹³C-microcosm-derived rates to field-derived rates of the first approach. Further advantage of the use of ¹³C-labels in microcosms is that novel metabolites can be linked more easily to specific mother compounds even in complex systems. This was achieved using alluvial sediments where ¹³C-acenaphthyl methylsuccinate was identified as transformation product of the anaerobic degradation of acenaphthene.     

Organic contaminant behavior during rapid infiltration of secondary wastewater at the phoenix 23rd avenue project

Movement of trace organic pollutants during rapid infiltration of secondary wastewater for groundwater recharge was studied at the 23rd Avenue Rapid Infiltration Project in Phoenix, Arizona. Samples of the wastewater applied to the spreading basins and of renovated water taken from monitoring wells were characterized for priority pollutants and other specific organic compounds using gas chromatography/mass spectrometry. The concentrations of organic constituents were affected by volatilization, biodegradation and sorption processes. Nonhalogenated aliphatics and aromatic hydrocarbons exhibited concentration decreases of 50–99% during soil percolation. Halogenated organic compounds were generally removed to a lesser extent. Concentrations of trichloroethylene, tetrachloroethylene, and pentachloroanisole appeared to be significantly higher in the renovated water than in the basin water, reasons for this behavior remain unclear. Many organic contaminants were detected in the groundwater indicating such systems should be designed to localize contamination of the aquifer. Chlorination of the wastewater had no significant effect on concentrations and types of trace organic compounds.     

Hydrogeochemische Entwicklung in einem pleistoz?nen Porengrundwasserleiter beeinflusst durch Leckage

At a former industrial site in north-western Germany, the lower Quaternary aquifer was investigated with respect to hydrogeology and hydrogeochemistry. The upper aquifer was contaminated by chlorinated hydrocarbons (CHCs) from a chemical factory and remediation attempts have been carried out for over 10 years. The hydraulic conditions of both aquifers were characterized with hydraulic head measurements in March 2012. In addition, three sampling campaigns in 2009, 2011 and 2012 helped to describe the geochemistry of the lower aquifer. In the lower aquifer downstream of the remediation area, influence of contamination as well as the remediation measures should also be visible. In order to demonstrate leakage from the upper aquifer and to show the development of the geochemical characteristics, a transport and reaction model was developed using PhreeqeC. These simulations strengthen the assumption of a leakage scenario. This leads to unexpected nitrate concentrations, products of degradation of organic substances and signals of former input of waters with high sodium contents. Ion exchange and degradation of organic substances were identified as the most important processes that improve groundwater quality in the lower aquifer downstream of the remediation area.     

Fate of N-nitrosomorpholine in an anaerobic aquifer used for managed aquifer recharge: a column study

The fate of N-nitrosomorpholine (NMOR) was evaluated at microgram and nanogram per litre concentrations. Experiments were undertaken to simulate the passage of groundwater contaminants through a deep anaerobic pyritic aquifer system, as part of a managed aquifer recharge (MAR) strategy. Sorption studies demonstrated the high mobility of NMOR in the Leederville aquifer system, with retardation coefficients between 1.2 and 1.6. Degradation studies from a 351 day column experiment and a 506 day stop-flow column experiment showed an anaerobic biologically induced reductive degradation process which followed first order kinetics. A biological lag-time of less than 3 months and a transient accumulation of morpholine (MOR) were also noted during the degradation. Comparable half-life degradation rates of 40-45 days were observed over three orders of magnitude in concentration (200 ng L⁻¹ to 650 μg L⁻¹). An inhibitory effect on microorganism responsible to the biodegradation of NMOR at 650 μg L⁻¹ or a threshold effect at 200 ng L⁻¹ was not observed during these experiments.     

Testfeld Süd: Einrichtung der Testfeldinfrastruktur und Erkundung hydraulisch-hydrogeochemischer Parameter des Grundwasserleiters

A former gasification plant with a variety of organic contaminants within the aquifer serves as a field test site. Both contaminants in phase (contamination source) and dissolved (contaminant plume) can be detected. After extending the test site infrastructure various methods for the investigation of groundwater flow and transport have been applied and compared. The geometry of the aquifer is variable and a pronounced heterogeneity of the hydraulic conductivity can be observed. The influence of the sedimentary setting on the structure of the aquifer is shown. A relation between discrete grain size distributions and the petrographical composition of the aquifer material is established. Using this relation, the sorption properties of the aquifer can be derived. Following the first measurements, the observed differential spreading of pollutants within the contaminant plume is influenced by microbial degradation. Further field tests to investigate the biodegradation rates are proposed.     

Grundwasser-Zirkulations-Brunnen (GZB) zur In-situ-Grundwassersanierung

In recent years experimental investigations regarding enhanced remediation of contaminated aquifers by employing vertical circulation flow systems were carried out at the Institute for Hydromechanics (IfH), University of Karlsruhe. These investigations were focused on large scale three-dimensional remediation experiments with a groundwater circulation well (GZB) at field-like conditions in the research facility VEGAS, University of Stuttgart. Small scale laboratory experiments in columns and a two-dimensional flume at the IfH as well as field experiments completed the multiple-scale investigations. The experimental results on different scales showed the dominance of the mass transfer processes on the in situ remediation of a contamination source and their dependence on the flushing intensity. The remediation progress could be explained and also predicted by the mass removal coefficient. The GZB is a robust and well controllable technology, whose operation could be adapted well to natural aquifer conditions and the physical-chemical properties of the contaminants. Developing different efficiency numbers results of the experiments and generally remediation variants could be evaluated due to their effect and expenditure.     

Principles of organic contaminant behavior during artificial recharge

The behavior of a variety of organic contaminants having low molecular weight has been observed during groundwater recharge with reclaimed water. The evidence is site-specific, but is believed to have broader implications regarding the general behavior of organic contaminants in groundwater. The movement of specific contaminants such as chloroform and chlorobenzene is retarded with respect to that of a conservative tracer such as chloride. The measured retardation factors are approximately 3 and 35 for chloroform and chlorobenzene, respectively. The retardation is caused by the sorption of the solute, apparently by the organic constituents of the soil material. The magnitude of the retardation factor of an organic solute can be predicted approximately from knowledge of the organic carbon content of the aquifer material and the octanol-water partition coefficient of the solute. Sorption also contributes to attenuation (damping) of concentration fluctuations. It is shown that the degree of attenuation depends strongly on the retardation factor, the distance traveled, and the hydrogeologic characteristics of the aquifer. There is evidence of biodegradation of organic solutes in the vicinity of the recharge well.     

Carbon isotope effects associated with Fenton-like degradation of toluene: potential for differentiation of abiotic and biotic degradation

Hydrogen peroxide (H(2)O(2))-mediated oxygenation to enhance subsurface aerobic biodegradation is a frequently employed remediation technique. However, it may be unclear whether observed organic contaminant mass loss is caused by biodegradation or chemical oxidation via hydroxyl radicals generated during catalyzed Fenton-like reactions. Compound-specific carbon isotope analysis has the potential to discriminate between these processes. Here we report laboratory experiments demonstrating no significant carbon isotope fractionation during Fenton-like hydroxyl radical oxidation of toluene. This implies that observation of significant isotopic fractionation of toluene at a site undergoing H(2)O(2)-mediated remediation would provide direct evidence of biodegradation. We applied this approach at a field site that had undergone 27 months of H(2)O(2)-mediated subsurface oxygenation. Despite substantial decreases (>68%) in groundwater toluene concentrations carbon isotope signatures of toluene (delta(13)C(tol)) showed no significant variation (mean=-27.5+/-0.3 per thousand, n=13) over a range of concentrations from 11.1 to 669.0 mg L(-1). Given that aerobic degradation by ring attack has also been shown to result in no significant isotopic fractionation during degradation, at this site we were unable to discern the mechanism of degradation. However, such differentiation is possible at sites where aerobic degradation by methyl group attack results in significant isotopic fractionation.     

Long-term observations on the influence of groundwater level variations on BTEX concentrations in groundwater

A long-term study on natural attenuation and remediation in soil and groundwater at the former military base Schäferhof-Süd (Niedersachsen) was performed at a former gasoline filling station. At this locality, a large residual source of benzene, toluene, ethylbenzene, xylenes (BTEX) and additional petroleum hydrocarbons is present in the soil. BTEX-concentrations in the groundwater and their correlation with groundwater level variations were monitored for three years. Within the monitoring period, a very dry summer was recorded, which caused the groundwater level to drop by 1.7 m and the BTEX concentrations to increase from 240 µg/l to 1300 µg/l at the site of contamination. The microbial degradation of BTEX was documented by data on consumption of electron acceptors (oxygen, nitrate or sulphate) and production of reduced products (Fe(II), methane). The degradation is further supported by the detection of metabolites. Therefore, the increasing BTEX concentrations were not a consequence of limited biological degradation.     

Significance of biomass support particles in laboratory studies on microbial degradation of organic chemicals in aquifers

In degradation studies of xenobiotics in groundwater environments from where only water samples can be obtained (e.g. established deep groundwater wells, inhomogeneous formations as boulder aquifers, or consolidated aquifers), solids might be added as biomass support materials. The importance of biomass support materials as quartz sand, rock wool and crushed tiles on the degradation of 8 aromatic hydrocarbons (benzene, toluene, o-xylene, 1,2-dichlorobenzene (1,2-DCB), 1,4-dichlorobenzene (1,4-DCB), naphthalene, biphenyl and nitrobenzene) was investigated in experiments with groundwater collected from two aerobic aquifers (Vejen and Grindsted, Denmark). Experiments with only groundwater as well as groundwater suspensions with aquifer sediment were run as references. It was impossible to adjust pH to the desired level in the experiments with crushed tiles, where also substantial sorption of the test compounds and server clogging of filters used in sampling occurred, and this material was therefore useless as biomass support material. Presence of rock wool supported growth of bacteria and increased the degradation (in terms of rates and number of compounds degraded) compared with experiments with groundwater only. However, the degradation was less and the degradation patterns varied more than in the presence of aquifer sediment. Quartz sand gave the most promising results with respect to growth of bacteria, and the degradation patterns of most of the compounds were similar to those obtained in experiments including aquifer sediments, although the latter showed the most substantial degradation. This study suggests that in case aquifer sediment is not available, quartz sand should be added as biomass support material in studies on degradation of organic xenobiotics in groundwater environments.     

Evidence for cooxidation of polynuclear aromatic hydrocarbons in soil

The effect of constituent matrix on the degradation of hydrocarbons was characterized and evaluated within the context of cooxidation. Current information concerning the cooxidation process applied to hydrocarbons was evaluated and results were used to define a laboratory approach for studying the effects of constituent matrix on degradation rates of 13 polynuclear aromatic hydrocarbons (PAHs) in soil. Four matrices were studied: (1) single constituents applied and incubated singly; (2) a synthetic mixture of PAHs applied and incubated together; (3) a mixture of oil refinery wastes; (4) and a creosote wood preserving waste. Initial soil concentrations of constituents were similar for each matrix evaluated. One soil was used, a Kidman fine sandy loam (Haplustoll, Utah). Incubation conditions and extraction and analysis methods were similar among the studies. Four and 5-ring PAHs were found to disappear more rapidly from soils amended with complex wastes, while degradation rates for 3-ring compounds in all matrices were similar. These results can be interpreted in the context of cooxidation and suggest a potential tool for bioremediation of PAH contaminated soils and the simultaneous protection of groundwater resources through reduction or mitigation of groundwater contamination due to vadose zone-associated PAHs.     

Hydrogeologische Untersuchungen bei der Anwendung von Monitored Natural Attenuation (MNA) an einem BTEX-kontaminierten Grundwasserleiter

A prominent feature of Monitored Natural Attenuation (MNA) is the prediction of the fate of contaminants from field data. The validity of field data was evaluated by hydrogeological investigations at a BTEX-contaminated site. Results from the following investigations were taken into consideration: Pump test, bore hole data, and measurements of precipitation and groundwater level changes. Moreover, changes in contaminant concentrations and changes in hydraulic gradients were investigated. There was a statistically significant dependence of contaminants on a fluctuating groundwater level (±1.4m), which had different effects: at high groundwater levels, contaminant concentrations in the near-source area were lower and were associated with a plume extension downstream. Hydraulic gradient fluctuations between 1.5‰ and 15.1‰ were observed. Lower hydraulic gradients prevailed in the source area at high groundwater levels, whereas the downstream area had steeper gradients. The direction of hydraulic gradients varied between 12° and 67°. Accounting for these features will allow an evaluation of field data in support of MNA. Hydrogeologic investigations proved to be of importance for a subsequent assessment of NA processes in the aquifer.     

Groundwater pollutants from underground coal gasification

The purpose of this study was to determine the contaminants released to groundwaters as a result of the underground gasification of lignite and determine the ability of the surrounding strata to moderate their impact. Groundwater pollutants principally arise from ash leachate and condensed vapors in surrounding strata. Ash was found to yield sulfate, calcium, and hydroxide while condensed vapors contributed organics and ammonia as major changes to water quality. The organics consisted of mostly polynuclear aromatic hydrocarbons. Phenols were not major organic components. Lignite and clay strata were studied to determine their ability to sorb the groundwater contaminants. Both types of strata were effective in sorbing organics and ammonia. The behavior could be described by Freundlich isotherms. Divalent cations were released by ion exchange with monovalent cations. Anions had little affinity for the strata. Relatively little migration of ammonia and most of the organics was predicted as compared with calcium, sulfate, and some non-sorbable organics.     

Dynamics of solutes and dissolved oxygen in shallow urban groundwater below a stormwater infiltration basin

Artificial recharge of urban aquifers with stormwater has been used extensively in urban areas to dispose of stormwater and compensate for reduced groundwater recharge. However, stormwater-derived sediments accumulating in infiltration beds may act as a source of dissolved contaminants for groundwater. Concentrations of hydrocarbons, heavy metals, nutrients and dissolved oxygen (DO) were monitored at multiple depths in shallow groundwater below a stormwater infiltration basin retaining large amounts of contaminated organic sediments. Multilevel wells and multiparameter loggers were used to examine changes in groundwater chemistry occurring over small spatial and temporal scales. Rainfall events produced a plume of low-salinity stormwater in the first 2 m below the groundwater table, thereby generating steep vertical physico-chemical gradients that resorbed during dry weather. Heavy metals and hydrocarbons were below reference concentrations in groundwater and aquifer sediments, indicating that they remained adsorbed onto the bed sediments. However, mineralization of organic sediments was the most probable cause of elevated concentrations of phosphate and DOC in groundwater. DO supply in groundwater was severely limited by bed respiration which increased with temperature. Cold winter stormwater slightly re-oxygenated groundwater, whereas warm summer stormwater lowered DO concentrations in groundwater. Among several results provided by this study, it is recommended for management purposes that infiltration practices should minimize the contact between inflow stormwater and organic sediments retained in infiltration basins.     

Phytoremediation potential of willow trees for aquifers contaminated with ethanol-blended gasoline

Ethanol-blended gasoline has been used in Brazil for 20 years and, probably, is going to be more widely used in North America due to the MtBE environmental effects on groundwater. The potential impacts caused by the presence of ethanol in UST spills are related to the co-solvency effect and the preferential degradation of ethanol over the BTEX compounds. These interactions may increase the length of dissolved hydrocarbon plumes and the costs associated with site remediation. This study investigates the advantages of phytoremediation to overcome the problems associated with the presence of ethanol in groundwater contaminanted with gasoline-ethanol mixtures. Experiments were performed under lab conditions with cuttings of Willow tree (Salix babylonica) cultivated hydroponically. Results showed that the cuttings were able to reduce ethanol and benzene concentrations by more than 99% in less than a week. The uptake of both contaminants was confirmed by blank controls and was significantly related to cuttings transpiration capacity. Sorption onto roots biomass also markedly affected the behavior of contaminants in solution. Experiments to evaluate plants' toxicity to ethanol indicated that plants were only affected when aqueous ethanol concentration reached 2000mgl(-1). Results suggest that phytoremediation can be a good complement to intrinsic remediation in shallow aquifer sites contaminated with ethanol-blended gasoline spills.     

受污染含水层抽水——处理最优化及对地下水污染生物修复的基本认识

本文讨论了修复受污染含水层的抽水———处理技术的最优化问题,提出建立抽水———处理最优化模型时应注意的三个要素,以确定含水层修复的最佳战略。认为抽水———处理技术是一种好方法。涉及与地下水污染有关的问题,需要能够模拟在地下进行的生物修复和污染物运移的计算机模型。近年来,研发了许多数字程序来认识生物降解/生物变换过程。可是,对这种生物修复系统进行数值模拟,总是需要做出确实的计算上的努力。如果有一些恰当的解析解可作为适宜应用的筛选手段,则便于在详细研究以前进行生物修复评价。本文提出了模拟生物修复和有反应运移的解析模型的文献评论。     

Comparison of the fuel oil biodegradation potential of hydrocarbon-assimilating microorganisms isolated from a temperate agricultural soil

Strains of hydrocarbon-degrading microorganisms (bacteria and fungi) were isolated from an agricultural soil in France. In a field, a portion was treated with oily cuttings resulting from the drilling of an onshore well. The cuttings which were spread at the rate of 600 g HC m-2 contained 10% of fuel oil hydrocarbons (HC). Another part of the field was left untreated. Three months after HC spreading, HC adapted bacteria and fungi were isolated at different soil depths in the two plots and identified. The biodegradation potential of the isolated strains was monitored by measuring the degradation rate of total HC, saturated hydrocarbons, aromatic hydrocarbons and resins of the fuel. Bacteria of the genera Pseudomonas, Brevundimonas Sphingomonas, Acinetobacter, Rhodococcus, Arthrobacter, Corynebacterium and fungi belonging to Aspergillus, Penicillium, Beauveria, Acremonium, Cladosporium, Fusarium, and Trichoderma were identified. The most active strains in the assimilation of saturates and aromatics were Arthrobacter sp., Sphingomonas spiritivorum, Acinetobacter baumanii, Beauveria alba and Penicillum simplicissimum. The biodegradation potential of the hydrocarbon utilizing microorganisms isolated from polluted or unpolluted soils were similar. In laboratory pure cultures, saturated HC were more degraded than aromatic HC, whereas resins were resistant to microbial attack. On an average, individual bacterial strains were more active than fungi in HC biodegradation.     

Ist Monitored Natural Attenuation (MNA) eine Option für LCKW-kontaminierte Grundwasserleiter?

An investigation of the chlorinated volatile organic compound (CVOC) biodegradation processes at a reference site with a contaminant plume of 4?km length in a terrace gravel aquifer has revealed that simultaneously spilled non-chlorinated contaminants (which serve as electron donors for reductive dechlorination) caused a transformation of the parent contaminants to cis-1,2-dichloroethene (cDCE) and vinylchloride (VC). Secondary spills in the area of the plume have lead to a complex pattern of different redox zones. In deeper areas of the aquifer, a lack of electron donors due to their migration properties could be observed. The complete mineralization at the plume tip seems to occur under anaerobic conditions via oxidative biodegradation pathways, or under aerobic conditions. High waters of the nearby Rhine river cause a staggering of the plume tip which is likely accompanied by growth of the aerobic fringe area. Pump and treat measures to capture the source area and dissolved plume have substantially altered the biodegradation conditions. On the basis of the investigation results, a simple model was developed to evaluate whether MNA may be an option at CVOC contaminated sites.