Grindsted Landfill Research Articles

Toxicity of Organic Chemical Pollution in Groundwater Downgradient of a Landfill (Grindsted, Denmark)

The aim of the present study was to describe the occurrence and distribution of toxicity related to organic chemical contaminants in the leachate plume downgradient of the Grindsted Landfill (Denmark). A total of 27 groundwater samples were preconcentrated by solid-phase extraction (SPE) using XAD-2 as the resin material. This treatment effectively eliminated sample matrix toxicity caused by inorganic salts and natural organic compounds and produced an aqueous concentrate of the nonvolatile chemical contaminants. The SPE extracts were tested in a battery of standardized short-term aquatic toxicity tests with luminescent bacteria (Vibrio fischeri), algae (Selenastrum capricornutum), and crustaceans (Daphnia magna). Additional genotoxicity tests were made using the umuC test (Salmonella typhimurium). Biotests with algae and luminescent bacteria were the most sensitive tests. On the basis of results with these two bioassays, it was concluded that SPE extracts of groundwater collected close to the landfill we...

Fate of MCPP and atrazine in an anaerobic landfill leachate plume (Grindsted, Denmark)

The fate of the two pesticides MCPP (mecoprop) and atrazine was investigated in an anaerobic aquifer downgradient from the Grindsted Landfill, Denmark, by means of a field injection experiment, in situ microcosms and laboratory batch experiments. The redox conditions in the experiments were dominated by iron reduction, but also methanogenesis and sulfate reduction occurred closest to the landfill. No degradation nor sorption was observed for the two pesticides in any of the biologically active experiments. In microbially inhibited laboratory experiments, supplied with sodium azide as a sterilizing agent, a chemical degradation of atrazine occurred.

An anaerobic field injection experiment in a landfill leachate plume, Grindsted, Denmark: 1. Experimental setup, tracer movement, and fate of aromatic and chlorinated compounds

A continuous, natural‐gradient field injection experiment, involving 18 xenobiotic compounds and bromide as tracers, was performed in the anaerobic region of a leachate plume downgradient from the Grindsted Landfill, Denmark. The injection lasted for 195 days, and within this period a continuous cloud was established. Over a period of 924 days the cloud movement was monitored in approximately 70 discrete sampling points in the central part of the cloud, and the spatial distribution was described by seven cloud snapshots involving 400–700 sampling points. The bromide cloud movement closely followed the varying flow direction predicted by the water table measurements. Moment analysis showed decreasing tracer flow velocities and reduced capture of bromide mass with time, which may be explained by varying flow conditions (direction, hydraulic gradient) and the heterogeneous geological conditions in the sandy aquifer. Naphthalene, having the highest log Kow value, was the most retarded compound, with a retardation of less than 10%. Therefore sorption was not considered to be a significant attenuation process for any of the compounds studied. Transformation under iron‐reducing conditions was observed for toluene, o‐xylene, TeCM, 1,1,1‐TCA, PCE, and TCE, while transformation of benzene and napthalene was not detected in the aquifer within the time frame of this study. First‐order transformation rates were in the range of 0.028–0.039 d−1 and 0.0014–0.0028 d−1 for the aromatic compounds toluene and o‐xylene, respectively. The rates for the chlorinated aliphatic compounds, tetrachloromethane, 1,1,1‐ trichloroethane, tetrachloroethylene, and trichloroethylene, were >0.7 d−1, 0.0044–0.0054 d−1, 0.0012–0.0038 d−1, and 0.0003–0.001 d−1, respectively. Long lag periods and slow transformation rates were observed for some of the compounds, suggesting that lack of transformation reported in the literature may be attributable to short experimental periods in those studies.

An anaerobic field injection experiment in a landfill leachate plume, Grindsted, Denmark: 2. Deduction of anaerobic (methanogenic, sulfate‐, and Fe (III)‐reducing) redox conditions

Redox conditions may be environmental factors which affect the fate of the xenobiotic organic compounds. Therefore the redox conditions were characterized in an anaerobic, leachate‐contaminated aquifer 15–60 m downgradient from the Grindsted Landfill, Denmark, where an field injection experiment was carried out. Furthermore, the stability of the redox conditions spatially and over time were investigated, and different approaches to deduce the redox conditions were evaluated. The redox conditions were evaluated in a set of 20 sediment and groundwater samples taken from locations adjacent to the sediment samples. Samples were investigated with respect to groundwater chemistry, including hydrogen and volatile fatty acids (VFAs) and sediment geochemistry, and bioassays were performed. The groundwater chemistry, including redox sensitive species for a large number of samples, varied over time during the experimental period of 924 days owing to variations in the leachate from the landfill. However, no indication of change in the redox environment resulting from the field injection experiment or natural variation was observed in the individual sampling points. The methane, Fe(II), hydrogen, and VFA groundwater chemistry parameters strongly indicated a Fe(III)‐reducing environment. This was further supported by the bioassays, although methane production and sulfate‐reduction were also observed in a few samples close to the landfill. On the basis of the calculated carbon conversion, Fe(III) was the dominant electron acceptor in the region of the aquifer, which was investigated. Because of the complexity of a landfill leachate plume, several redox processes may occur simultaneously, and an array of methods must be applied for redox characterization in such multicomponent systems.

Degradation of Aromatic and Chlorinated Aliphatic Hydrocarbons in the Anaerobic Part of the Grindsted Landfill Leachate Plume: In Situ Microcosm and Laboratory Batch Experiments

AbstractThe fate of seven aromatic and four chlorinated aliphatic compounds was studied using in situ microcosm (ISM) and laboratory batch (LB) experiments performed at six distances along a flow line in the anaerobic leachate plume downgradient of the Grindsted Landfill, Denmark. The redox conditions were dominated by iron reduction in this part of the plume (15 to 60 m downgradient of the landfill); however, methanogenesis and sulfate reduction also took place closer to the landfill (15 to 45 m). Generally, good accordance was found between the degradation of the compounds determined by the two experimental approaches, considering the limitations of the experimental periods (up to 220 days for the ISM and up to 537 days for the LB). Of the aromatic compounds, toluene, o‐ and m/p‐xylene were degraded, while benzene, ethylbenzene, and naphthalene were not degraded, neither in the ISM nor in the LB at any distance from the landfill. All the chlorinated aliphatic compounds, (TeCM, 1,1,1‐TCA, PCE, and TCE) were degrad‐able; however, the degradation potential for PCE and TCE depended on the distance from the landfill. For most compounds, both approaches gave results comparable to those of the natural gradient field injection experiment performed in the same plume. This suggests that laboratory batch experiments, which are easier to run than ISM experiments, may be a useful tool in determining the degradability of mono aromatic hydrocarbons and chlorinated aliphatic hydrocarbons under strongly anaerobic conditions in the investigation of natural attenuation in landfill leachate plumes.

H2 Concentrations in a Landfill Leachate Plume (Grindsted, Denmark): In Situ Energetics of Terminal Electron Acceptor Processes

Empirical H2 concentration ranges are currently related to specific redox processes, assuming steady-state conditions at which only one microbiologically mediated redox process occurs due to competetive exclusion of others. Here the first H2 data from a landfill leachate plume are presented, and an alternative partial equilibrium approach is used. The approach implies that TEAPs (terminal electron-accepting processes) occur at negative ΔGr values, close to thermodynamic equilibrium, and that the fermentative H2 production is overall rate limiting. It eliminates the steady-state prerequisite and may explain the occurrence of concomitant TEAPs. Concentrations of H2 and redox process reactants and products were measured in 52 sampling points, downgradient of the Grindsted Landfill (Denmark), and used to calculate in situ ΔGr values of TEAPs, assuming partial equilibrium. H2 generally ranged from 0.004 to 0.88 nM, with most values around 0.2 nM. Fe reduction was, according to the empirically defined ranges, the most prominent TEAP, but concomitant methanogenesis and sulfate reduction occurred as well. This indicated a need for an alternative approach to explaining the H2 distribution, and the measured H2 concentrations are viewed as being controlled by a partial equilibrium. A derived theoretical relation between H2 concentrations and temperature indicates temperature effects to be more important than currently appreciated. Calculated in situ ΔGr values can, combined with a threshold value, predict which TEAPs can occur via H2 oxidation. For our samples, ΔGr for methanogenesis was always >−7 kJ/mol, and CO2 reduction should only occur in stagnant porewater at higher H2 concentrations or by direct interspecies transfer. In contrast, sulfate and Fe reduction occur close to or slightly below a threshold of −7 kJ/mol H2 and may occur concomitantly at partial equilibrium.

Concentration Data and Dimensionality in Groundwater Models: Evaluation Using Inverse Modelling

A three-dimensional inverse groundwater flow and transport model that fits hydraulic-head and concentration data simultaneously using nonlinear regression is presented and applied to a layered sand and silt groundwater system beneath the Grindsted Landfill in Denmark. The aquifer is composed of rather homogeneous hydrogeologic layers. Two issues common to groundwater flow and transport modelling are investigated: 1) The accuracy of simulated concentrations in the case of calibration with head data alone; and 2) The advantages and disadvantages of using a two-dimensional cross-sectional model instead of a three-dimensional model to simulate contaminant transport when the source is at the land surface Results show that using only hydraulic heads in the nonlinear regression produces a simulated plume that is profoundly different from what is obtained in a calibration using both hydraulic-head and concentration data. The present study provides a well-documented example of the differences that can occur. Representing the system as a two-dimensional cross-section obviously omits some of the system dynamics. It was, however, possible to obtain a simulated plume cross-section that matched the actual plume cross-section well. The two-dimensional model execution times were about a seventh of those for the three-dimensional model, but some difficulties were encountered in representing the spatially variable source concentrations and less precise simulated concentrations were calculated by the two-dimensional model compared to the three-dimensional model. Summed up, the present study indicates that three-dimensional modelling using both hydraulic heads and concentrations in the calibration should be preferred in the considered type of transport studies.

Effects of Sampling Well Construction on H2Measurements Made for Characterization of Redox Conditions in a Contaminated Aquifer

Measurement of hydrogen, H2, has been suggested for characterization of redox levels in groundwater and has recently been used in the delineation of redox processes in contaminated aquifer. In this investigation, we evaluate the influence of materials and age of the well on the H2 measurements performed in a leachate-contaminated sandy aquifer at the Grindsted Landfill, Denmark, Four types of small diameter wells were tested, covering a range of materials (teflon, PVC, black iron, and stainless steel) and installation methods (driven wells and bailer techniques). The results suggest that the following precautions are taken in order to obtain valid measurements of H2: (1) all iron parts should be avoided as well materials, (2) PVC, teflon, and probabaly stainless steel are suitable materials for wells, (3) wells for monitoring H2 levels shall rest for a period from installation till sampling (our experiences indicate approximately 3 months) before their readings can be trusted, and (4) installation of wells or heavy mechanical work in the subsoil can affect the H2 levels in nearby wells.

Correlating phospholipid fatty acids (PLFA) in a landfill leachate polluted aquifer with biogeochemical factors by multivariate statistical methods

Different multivariate statistical analyses were applied to phospholipid fatty acids representing the biomass composition and to different biogeochemical parameters measured in 37 samples from a landfill contaminated aquifer at Grindsted Landfill (Denmark). Principal component analysis and correspondence analysis were used to identify groups of samples showing similar patterns with respect to biogeochemical variables and phospholipid fatty acid composition. The principal component analysis revealed that for the biogeochemical parameters the first principal component was linked to the pollution effect and to redox processes and the second principal component described the geological and geochemical features of the samples. Dependent on the data transformation of the phospholipid fatty acid profiles in either absolute concentrations (logarithm transformed) or in mol% of total phospholipid fatty acids, different groups of samples and outliers were revealed by the principal component analysis. The principal component analysis on data in absolute concentrations revealed that many phospholipid fatty acids reflected the pollution effect on the biomass composition. In contrast, the phospholipid fatty acids in mol% divided the samples into one group of the more polluted samples and another with the nearly unpolluted samples. The important phospholipid fatty acids for this grouping were mainly a few of the normal saturated phospholipid fatty acids (10:0, 16:0 and 18:0). Discriminant analysis was used to allocate samples of phospholipid fatty acids into predefined classes. A large percentages of samples were classified correctly when discriminating samples into groups of dissolved organic carbon and specific conductivity, indicating that the biomass is highly influenced by the pollution. In contrast, the discriminant analysis revealed that on the basis of the profiles of phospholipid fatty acids no good discrimination between samples showing dominant sulfate reduction and dominant iron reduction could be made, nor between samples showing dominant nitrate reduction and aerobic respiration. Partial least square analysis related the phospholipid fatty acids data to the biogeochemical parameters assuming linear relationships. After selection of the optimal phospholipid fatty acid combination by genetic algorithms, good partial least squares models with low prediction errors were gained primarily between the biogeochemical parameters describing total contents of carbon, pH and chloride. The models predicting specific activity in terms of, e.g., sulfate reduction activity in a sample had relatively higher prediction errors and low correlation coefficients. This indicates that the phospholipid fatty acid profiles from complex habitats have limited value for identifying more specific microbial populations.

Distribution of redox-sensitive groundwater quality parameters downgradient of a landfill (Grindsted, Denmark)

The leachate plume stretching 300 m downgradient from the Grindsted Landfill (Denmark) has been characterized in terms of redox-sensitive groundwater quality parameters along two longitudinal transects (285 samples). Variations in the levels of methane, sulfide, iron(II), manganese(II), ammonium, dinitrogen oxide, nitrite, nitrate, and oxygen in the groundwater samples indicate that methane production, sulfate reduction, iron reduction, manganese reduction, and nitrate reduction take place in the plume. Adjacent to the landfill, methanogenic and sulfate-reducing zones were identified, while aerobic environments were identified furthest away from the landfill. In between, different redox environments, including apparent transition zones, were identified in a sequence in accordance with the thermodynamic principles. The redox zones are believed to constitute an important chemical framework for the attenuation processes in the plume

Distribution of Organic Compounds from Municipal Solid Waste in the Groundwater Downgradient of a Landfill (Grindsted, Denmark)

The distribution of organic compounds in the leachate plume downgradient of the Grindsted Landfill was mapped along two 300 m long transects (285 groundwater samples). At the border of the landfill, elevated concentrations of dissolved organic matter 30-110 mg of C L -1 (measured as nonvolatile organic carbon, NVOC) were found. In a distance of 130 m downgradient of the landfill, the NVOC had decreased to background level, which is 1-3 mg of C L -1 . More than 15 organic compounds were identified in the groundwater at the downgradient border of the landfill with benzene, toluene, ethylbenzene, and xylenes as dominating. No pesticides were identified, but some phenoxy acids, which could be metabolites of known pesticides, were found. In a distance of approximately 60 m from the landfill, most of the specific organic compounds were no longer detectable. Since dilution and sorption apparently cannot account for the disappearance of the specific organic compounds within the first 60 m of the plume, it is proposed that the majority of the specific organic compounds were degraded in the anaerobic plume under methanogenic/sulfate-reducing or iron-reducing conditions. The investigation indicates that the aquifer has a substantial natural attenuation capacity