Experimental determination of efficiency of capping materials during consolidation of metal-contaminated dredged material

Capping has received considerable attention as a method to reduce contaminant transport from contaminated sediments and sub-aqueous disposed dredged materials. Consolidation of dredged material after capping can result in a substantial advection of pore water, into or through the capping layer. The effect of two different capping materials (crushed limestone and gneiss) on the transport of heavy metals and phosphorus during consolidation was studied with a novel experimental design. Capped dredged material was placed in a consolidation cell and pore water expelled during the consolidation was collected for chemical analysis. To support interpretation of the results from this test, interactions between the capping material and the dredged material were also studied in batch tests. The study revealed large differences in the capping efficiency (CE) between the two materials. Both materials were efficient caps for Fe and P (CE>99% with 2cm cap), while limestone also was efficient for Mn (CE>92% with 2cm cap). Contrary to what was expected, capping of dredged material with crushed gneiss increased the release of Ca, Mn, Co, Ni, Cd, and Cu, resulting in negative CE. The batch tests showed that leaching from the crushed gneiss was the source of the observed release of metals. The results also show that the high concentrations of heavy metals in the dredged material were immobilised, probably by sulphides. Protection against re-suspension and oxidation will therefore in many cases be the most important effect of the cap.     

Estimating contaminant-flushing rates for heterogeneous aquifers

Groundwater remediation evaluations typically include cleanup time projections. Current batch flushing-rate equations and analytical models often used to estimate groundwater cleanup rates typically underestimate cleanup times, with a major factor the flawed assumption of aquifer homogeneity. Numerical modelling of groundwater flow and contaminant transport is a time-intensive and costly alternative. An analytical modelling approach has been developed to quickly and cost effectively approximate realistic contaminant cleanup rates, factoring aquifer heterogeneity into the process. The mathematical relationships predict residual dissolved concentrations and average pumped concentrations over time, and also the time required to meet a concentration standard.     

A column method for determination of leaching of polycyclic aromatic hydrocarbons from aged contaminated soil

In this study a column leaching method for investigation of hydrophobic organic contaminants (HOCs) leaching from soil was developed. The method set-up is based on a recycled flow of sterile water through a soil column with a sedimentation chamber mounted on top of the column, in connection with on-line filtration. The combination of a sedimentation chamber and an on-line filtration enables the measurement of leaching concentrations from contaminated materials consisting of very fine particle fractions. In addition, by using on-line solid phase extraction, minute amounts of leaching HOCs may be captured and quantified with high accuracy and reproducibility. The method was applied successfully on a contaminated aged soil sample and the leaching behavior of seven PAHs, with three to six aromatic rings, was monitored for more than 1600 h under saturated conditions. The tested PAHs were fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)pyrene and benzo(ghi)perylene. The method proved to be reliable and capable of providing data on leachable amounts of the PAHs under field-like conditions and over a longer period of time. The results indicated low availability of the studied contaminants since only a minor fraction (0.3%) of the initial amount of PAHs in the soil was removed during the experiment (liquid/solid-ratio of 700 l/kg). Thus PAHs in aged contaminated soil are not to be expected to be released to any great extent only by leaching with water.     

2,4-二氯苯酚在土壤中的吸附及其批实验与柱实验的分配系数比较

为了研究2,4-二氯苯酚在土壤中的吸附及比较其批实验与柱实验的分配系数Kd,开展了2,4-二氯苯酚的批实验（不同液固比条件下）和柱实验。通过分析结果可知,在批实验中,不同液固比条件下2,4-二氯苯酚达到平衡的时间类似,都在60～70 h,吸附动力学曲线符合伪二级动力学方程,吸附规律是：液固比越大,平衡吸附量增大,反应速率常数K2减小,初始吸附速率常数减小;Kd随液固比增大而降低,范围在2.91～2.12 L/kg。柱实验结果表明,2,4-二氯苯酚的贯穿曲线可以很好地用化学非平衡模型来拟合,通过模型拟合得到的Kd值要低于批实验的结果。该研究对表征2,4-二氯苯酚在环境中的行为、预测其对土壤和地下水的污染及其治理提供了依据。     

Effect of dissolved organic matter and bacteria on contaminant transport in riverbank filtration

A mathematical model for the transport of hydrophobic organic contaminants in an aquifer under simplistic riverbank filtration conditions is developed. The model considers a situation where contaminants are present together with dissolved organic matter (DOM) and bacteria. The aquifer is conceptualized as a four-phase system: two mobile colloidal phases, an aqueous phase, and a stationary solid phase. An equilibrium approach is used to describe the interactions of contaminants with DOM, bacteria, and solid matrix. The model is composed of bacterial transport equation and contaminant transport equation. Numerical simulations are performed to examine the contaminant transport behavior in the presence of DOM and bacteria. The simulation results illustrate that contaminant transport is enhanced markedly in the presence of DOM and bacteria, and the impact of DOM on contaminant mobility is greater than that of bacteria under examined conditions. Sensitivity analysis demonstrates that the model is sensitive to changes of three lumped parameters: K+1 (total affinity of stationary solid phase to contaminants), K+2 (total affinity of DOM to contaminants), and K+3 (total affinity of bacteria to contaminants). In a situation where contaminants exist simultaneously with DOM and bacteria, contaminant transport is mainly affected by a ratio of K+1/K+2/K+3, which can vary with changes of equilibrium distribution coefficient of contaminants and/or colloidal concentrations. In riverbank filtration, the influence of DOM and bacteria on the transport behavior of contaminants should be accounted to accurately predict the contaminant mobility.     

A pragmatic approach for estimation of source-zone emissions at LNAPL contaminated sites

When considering natural attenuation as a remediation strategy at a site contaminated by a light non-aqueous phase liquid (LNAPL), it is important to consider the emission of contaminants from the source zone. A quantification of source-zone emissions is essential both for comparison with down-gradient mass fluxes to provide an estimate of fractional mass flux reduction, as well as for estimating the source lifetime. Because the spatial distribution of LNAPL at a field site is strongly dependent on both the spill circumstances and the heterogeneity of the geologic materials, which can be problematic for in-situ determination, alternative methods for estimating source-zone emissions are needed. In this work, a three-dimensional multiphase flow and transport modelling approach is used to investigate the relationship between the lateral extent of an LNAPL body and the emission of contaminants to groundwater at a contaminated site. For simulations involving an LNAPL release in an aquifer comprised of heterogeneous porosity and permeability distributions that were generated geostatistically, it is shown that a simple linear relationship exists between the lateral extent of the LNAPL body in the capillary fringe and the emission to the aqueous phase. The parameters describing the relationship are found to be linear functions of the groundwater flow velocity and the vertical infiltration rate. This site-specific relationship provides a simple method to estimate contaminant emissions to groundwater at LNAPL contaminated sites.     

Volatilization of contaminants from suspended sediment in a water column during dredging

Remedial dredging of contaminated bed sediments in rivers and lakes results in the suspension of sediment solids in the water column, which can potentially be a source for evaporation of hydrophobic organic compounds (HOCs) associated with the sediment solids. Laboratory experiments were conducted in an oscillating grid chamber to simulate the suspension of contaminated sediments and flux to air from the surface of the water column. A contaminated field sediment from Indiana Harbor Canal (IHC) and a laboratory-inoculated University Lake (UL) sediment, Baton Rouge, LA, were used in the experiments, where water and solids concentration and particle size distribution were measured in addition to contaminant fluxes to air. A transient model that takes into account contaminant desorption from sediment to water and evaporation from the water column was used to simulate water and sediment concentrations and air fluxes from the solids suspension. In experiments with both sediments, the total suspended solids (TSS) concentration and the average particle diameter of the suspended solids decreased with time. As expected, the evaporative losses were higher for compounds with higher vapor pressure and lower hydrophobicity. For the laboratory-inoculated sediment (UL), the water concentrations and air fluxes were high initially and decreased steadily implying that contaminant release to the water column from the suspended solids was rapid, followed by evaporative decay. For the field sediments (IHC), the fluxes and water concentrations increased initially and subsequently decreased steadily. This implied that the initial desorption to water was slow and that perhaps the presence of oil and grease and aging influenced the contaminant release. Comparison of the model and experimental data suggested that a realistic determination of the TSS concentration that can be input into the model was the most critical parameter for predicting air emission rates.     

Methods for sampling and analysis of tropospheric ethanol in gaseous and aqueous phases

In this paper, we report on techniques for sampling and measuring ethanol in both the gas and aqueous phases of the lower troposphere. In the gas phase, the best sampling conditions were ensured by adsorption on Hayesep Q with a Chromosorb W AW coated with LiCl dryer (method 1) or by cryogenic trapping (method 2). An intercomparison campaign showed good agreement between both methods under various conditions. Method 1 (adsorption on Hayesep Q with dryer) is easier to set up and to carry away from the laboratory. Method 2 (cryogenic trapping) requires longer sampling time (up to 60 min while method 1 requires only 10-15 min). Method 1 is adapted to high concentrations of ethanol (>20 ppb) and low relative humidity (<30%). Method 2 gives more accurate results than method 1 for low ethanol concentrations (1-20 ppb). Comparing these results to previous studies, it is clear that sampling with appropriate solid adsorbents or with stainless steel canisters (with appropriate humidified air and short storage time) is adapted to urban or industrial environments where ethanol concentrations are high. Cryogenic sampling must be preferred for remote places where ethanol concentrations are low. Three techniques were tested for sampling ethanol in the liquid phase, namely solid phase microextraction, purge and trap injection, and direct injection. Among those, the latter was chosen for field measurements of ethanol in rain samples at an urban location. These first ever results at an urban location show concentrations ranging from <1 to 5 microM in rains, which agree with the expected range of concentrations. However, the purge and trap method showed detection limits that were 50 times lower and should be preferred for liquid phase ethanol measurements in rural and remote locations. Combining cryogenic trapping for the gas phase (method 2) and direct injection for the liquid phase is convenient and well adapted for a multiphase study of ethanol in the atmosphere, where simultaneous measurements in both phases are needed.     

Oxidative dissolution of uraninite precipitated on Navajo sandstone

Column and batch experiments were conducted with sandstone and ground water samples to investigate oxidation of uraninite precipitated by microbially mediated reduction of U(VI), a contaminant in ground water beneath a uranium mill tailings site near Tuba City, AZ, USA. Uraninite precipitated together with mackinawite (FeS_0.9) because Fe(III) from the sandstone and sulfate, another contaminant in the water were reduced together with U(VI). After completion of U(VI) reduction, experiments were conducted to find out whether uraninite is protected by mackinawite against reoxidation. Uncontaminated ground water from the same site, containing 7 mg/l of dissolved oxygen, was passed through the columns or mixed with sandstone in batch experiments. The results showed that small masses of uraninite, 0.1 μg/g of sandstone, are protected by mackinawite from reoxidation. Uraninite masses on the order of 0.1 μg/g correspond to U(VI) concentrations of 0.5 mg/l, typically encountered in uranium contaminated ground waters. Mackinawite is an effective buffer and is formed in sufficient quantity to provide long-term protection of uraninite. Uranium concentrations in ground water passed through the columns are too low (4 μg/l) to distinguish between dissolution and oxidative dissolution of uraninite. However, batch experiments showed that uraninite oxidation takes place.     

Evaluating LNAPL contamination using GPR signal attenuation analysis and dielectric property measurements: practical implications for hydrological studies

Groundwater and sub-surface contamination by Light Non-Aqueous Phase Liquids (LNAPLs) is one of the industrial world's most pressing environmental issues and a thorough understanding of the hydrological, physical and bio-chemical properties of the sub-surface is key to determining the spatial and temporal development of any particular contamination event. Non-invasive geophysical techniques (such as electrical resistivity, electromagnetic conductivity, Ground-Penetrating Radar, etc.) have proved to be successful sub-surface investigation and characterisation tools with Ground-Penetrating Radar (GPR) being particularly popular. Recent studies have shown that the spatial/temporal variation in GPR signal attenuation can provide important information on the electrical properties of the sub-surface materials that, in turn, can be used to assess the physical and hydrological nature of the pore fluids and associated contaminants. Unfortunately, a high percentage of current LNAPL-related GPR studies focus on contaminant mapping only, with little emphasis being placed on characterising the hydrological properties (e.g., determining contaminant saturation index, etc.). By comparing laboratory-based, dielectric measurements of LNAPL contaminated materials with the GPR signal attenuation observed in both contaminated and 'clean' areas of an LNAPL contaminated site, new insights have been gained into the nature of contaminant distribution/saturation and the likely signal attenuation mechanisms. The results show that, despite some practical limitations of the analysis technique, meaningful hydrological interpretations can be obtained on the contaminant properties, saturation index and bio-degradation processes. A generalised attenuation/saturation model has been developed that describes the physical and attenuation enhancement characteristics of the contaminated areas and reveals that the most significant attenuation is related to smeared zone surrounding the seasonally changing water table interface. It is envisaged that the model will provide a basis for the interpretation of GPR data from analogous LNAPL contaminated sites and provide investigators with an appreciation of the merits and limitations of GPR-based, attenuation analysis techniques for hydrological applications.     

Modelling of sequential groundwater treatment with zero valent iron and granular activated carbon

Multiple contaminant mixtures in groundwater may not efficiently be treated by a single technology if contaminants possess rather different properties with respect to sorptivity, solubility, and degradation potential. An obvious choice is to use sequenced units of the generally accepted treatment materials zero valent iron (ZVI) and granular activated carbon (GAC). However, as the results of this modelling study suggest, the required dimensions of both reactor units may strongly differ from those expected on the grounds of a contaminant-specific design. This is revealed by performing an analysis for a broad spectrum of design alternatives through numerical experiments for selected patterns of contaminant mixtures consisting of monochlorobenzene, tetrachloroethylene, trichloroethylene (TCE), cis-1,2-dichloroethylene (cis-DCE), and vinyl chloride (VC). It is shown that efficient treatment can be achieved only if competitive sorption effects in the GAC unit as well as the formation of intermediate products in the ZVI unit are carefully taken into account. Cost-optimal designs turned out to vary extremely depending on the prevailing conditions concerning contaminant concentrations, branching ratios, and unit costs of both reactor materials. Where VC is the critical contaminant, due to high initial concentration or extensive production as an intermediate, two options are cost-effective: an oversized ZVI unit with an oversized GAC unit or a pure GAC reactor.     

A hybrid method for inverse characterization of subsurface contaminant flux

The methods presented in this work provide a potential tool for characterizing contaminant source zones in terms of mass flux. The problem was conceptualized by considering contaminant transport through a vertical “flux plane” located between a source zone and a downgradient region where contaminant concentrations were measured. The goal was to develop a robust method capable of providing a statement of the magnitude and uncertainty associated with estimated contaminant mass flux values.In order to estimate the magnitude and transverse spatial distribution of mass flux through a plane, the problem was considered in an optimization framework. Two numerical optimization techniques were applied, simulated annealing (SA) and minimum relative entropy (MRE). The capabilities of the flux plane model and the numerical solution techniques were evaluated using data from a numerically generated test problem and a nonreactive tracer experiment performed in a three-dimensional aquifer model. Results demonstrate that SA is more robust and converges more quickly than MRE. However, SA is not capable of providing an estimate of the uncertainty associated with the simulated flux values. In contrast, MRE is not as robust as SA, but once in the neighborhood of the optimal solution, it is quite effective as a tool for inferring mass flux probability density functions, expected flux values, and confidence limits.A hybrid (SA-MRE) solution technique was developed in order to take advantage of the robust solution capabilities of SA and the uncertainty estimation capabilities of MRE. The coupled technique provided probability density functions and confidence intervals that would not have been available from an independent SA algorithm and they were obtained more efficiently than if provided by an independent MRE algorithm.     

Near surface soil vapor clusters for monitoring emissions of volatile organic compounds from soils

The overall objective of this research was to develop and test a method of determining emission rates of volatile organic compounds (VOCs) and other gases from soil surfaces. Soil vapor clusters (SVCs) were designed as a low dead volume, robust sampling system to obtain vertically resolved profiles of soil gas contaminant concentrations in the near surface zone. The concentration profiles, when combined with a mathematical model of porous media mass transport, were used to calculate the contaminant flux from the soil surface. Initial experiments were conducted using a mesoscale soil remediation system under a range of experimental conditions. Helium was used as a tracer and trichloroethene was used as a model VOC. Flux estimations using the SVCs were within 25% of independent surface flux estimates and were comparable to measurements made using a surface isolation flux chamber (SIFC). In addition, method detection limits for the SVC were an order of magnitude lower than detection limits with the SIFC. Field trials, conducted with the SVCs at a bioventing site, indicated that the SVC method could be easily used in the field to estimate fugitive VOC emission rates. Major advantages of the SVC method were its low detection limits, lack of required auxiliary equipment, and ability to obtain real-time estimates of fugitive VOC emission rates.     

Co-injection of air and steam for the prevention of the downward migration of DNAPLs during steam enhanced extraction: an experimental evaluation of optimum injection ratio predictions

When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant, the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In a previous work, a theoretical model was developed to predict the optimum injection ratio of air to steam that would eliminate accumulation of DNAPL ahead of the temperature front and thus minimize the potential for downward migration. In this work, the theoretical model is summarized, and an experiment is presented in order to evaluate the optimum injection ratio prediction. In the experiment, a two-dimensional water saturated sand pack is contaminated with a known mass of TCE (DNAPL). The system is then remediated by co-injecting air and steam at the predicted optimum injection ratio, calculated based on the average contaminant soil concentration in the sand pack. Results for the co-injection of air and steam are compared to results for the injection of pure steam or pure air. Injection at the predicted optimum injection ratio for a volumetric average NAPL saturation, reduced accumulation of the contaminant ahead of the condensation front by over 90%, as compared to steam injection alone. This indicates that the optimum injection ratio prediction is a valuable tool for limiting the spreading of DNAPL during steam-enhanced extraction. Injection at the optimum injection ratio resulted in earlier recovery of contaminant than for steam injection alone. Co-injection of steam and air is also shown to result in much higher recovery rates than air injection alone.     

Establishing principal soil quality parameters influencing earthworms in urban soils using bioassays

Potential contamination at ex-industrial sites means that, prior to change of use, it will be necessary to quantify the extent of risks to potential receptors. To assess ecological hazards, it is often suggested to use biological assessment to augment chemical analyses. Here we investigate the potential of a commonly recommended bioassay, the earthworm reproduction test, to assess the status of urban contaminated soils. Sample points at all study sites had contaminant concentrations above the Dutch soil criteria Target Values. In some cases, the relevant Intervention Values were exceeded. Earthworm survival at most points was high, but reproduction differed significantly in soil from separate patches on the same site. When the interrelationships between soil parameters and reproduction were studied, it was not possible to create a good model of site soil toxicity based on single or even multiple chemical measurements of the soils. We thus conclude that chemical analysis alone is not sufficient to characterize soil quality and confirms the value of biological assays for risk assessment of potentially contaminated soils.     

Surface catalyzed Fenton treatment of bis(2-chloroethyl) ether and bis(2-chloroethoxy) methane

This study examined the feasibility of using surface catalyzed Fenton treatment to remediate soil and groundwater contaminated by the chlorinated ethers, bis(2-chloroethyl) ether (BCEE) and bis(2-chloroethoxy) methane (BCEM). Parameters that affect the contaminant loss rate such as porewater pH, hydrogen peroxide concentration, and solid/water ratio were systematically evaluated. Batch reactors were set-up utilizing either contaminated or uncontaminated soil, obtained from an industrial site in Moss Point, MS, that was mixed with synthetic groundwater containing the contaminants of interest. The results show an increase in contaminant reduction with a decrease in pH, an increase in hydrogen peroxide concentration, or an increase in the solid/water ratio. For a similar set of conditions, contaminant reduction was greater for systems utilizing contaminated soil as compared to the systems containing uncontaminated soil. In addition, specific oxygen uptake rates (SOURs) were measured for biomass, collected from an activated sludge plant, exposed to different dilutions of untreated and surface catalyzed Fenton treated water to evaluate whether residual BCEE, BCEM, and their co-contaminants as well as their oxidation by-products were potentially inhibitory or can potentially serve as a substrate for the biomass. The measured SOURs show that the surface catalyzed Fenton treatment enhanced the biodegradability of the contaminated groundwater and served as a substrate for the biomass.     

Citric acid-modified Fenton's reaction for the oxidation of chlorinated ethylenes in soil solution systems

Fenton's reagent, a solution of hydrogen peroxide and ferrous iron catalyst, is used for an in situ chemical oxidation of organic contaminants. Sulfuric acid is commonly used to create an acidic condition needed for catalytic oxidation. Fenton's reaction often involves pressure buildup and precipitation of reaction products, which can cause safety hazards and diminish efficiency. We selected citric acid, a food-grade substance, as an acidifying agent to evaluate its efficiencies for organic contaminant removal in Fenton's reaction, and examined the impacts of using citric acid on the unwanted reaction products. A series of batch and column experiments were performed with varying H2O2 concentrations to decompose selected chlorinated ethylenes. Either dissolved iron from soil or iron sulfate salt was added to provide the iron catalyst in the batch tests. Batch experiments revealed that both citric and sulfuric acid systems achieved over 90% contaminant removal rates, and the presence of iron catalyst was essential for effective decontamination. Batch tests with citric acid showed no signs of pressure accumulation and solid precipitations, however the results suggested that an excessive usage of H2O2 relative to iron catalysts (Fe2+/H2O2<1/330) would result in lowering the efficiency of contaminant removal by iron chelation in the citric acid system. Column tests confirmed that citric acid could provide suitable acidic conditions to achieve higher than 55% contaminant removal rates.     

Evaluating factors that influence microbial phenanthrene biodegradation rates by regression with categorical variables

To advance the accuracy of bioremediation measurements, it is useful before specific experiments to attribute or estimate the influence of both experimental as well as field conditions on the expected magnitudes of microbial degradation rate coefficients. This paper analyzes the numerical contribution, or influence, of categories of conditions, such as bacterial adaptive state, electron acceptor type, mixing, generalized sorption conditions, and biodegradation temperature, on published phenanthrene biodegradation rates as an example of our regression approach. A fundamental microbial degradation rate equation is transformed to an additive model, then using multiple linear regression on published data, coefficients (of categorical variables) and a linear model are presented that estimate first-order biodegradation rate coefficients to within a factor of 3. Numerical estimates of how much bacterial adaptive state and presence of a sorption phase, the two most statistically significant factors, alter the phenanthrene biodegradation rate are presented. The influence of some measurement or field conditions, for example, the influence of oxygen reduction versus optimal nitrate reduction, cannot be distinguished statistically given the available data and range. The regression model is tested using conditions from newly published papers to estimate a priori the expected rate, which compares very favorably to measurements reported in the papers. Due to limited published data and range for extreme cases, the current coefficients do not apply to degradation of very aged phenanthrene nor very low concentrations of electron acceptors. As estimating tools, however, the coefficients themselves and the regression approach have very beneficial roles in design of experiments for both laboratory and field settings. Our method can be applied to other PAHs as sufficient data become available.     

Freezing of a clayey silt contaminated with an organic solvent

In a study of water migration characteristics and organic contaminant transfer mechanisms in a freezing fine-grained saturated soil, a series of one-dimensional freezing tests were conducted on a clayey silt contaminated with a miscible, non-reactive organic compound, 1-propanol, at various concentrations. The experimental results indicate that the frost heave behaviour and solute rejection mechanisms of a soil contaminated with 1-propanol is similar to that of the same soil contaminated with sodium-chloride salt. It was found that 1-propanol is rejected from the pore for rates of cooling smaller than 4 ± 1°C/day. Diffusion appears to control contaminant redistribution in the unfrozen soil. Finally, there has been no contaminant redistribution in the frozen soil for periods up to 245 hours.     

Influence of temporally variable groundwater flow conditions on point measurements and contaminant mass flux estimations

Monitoring of contaminant concentrations, e.g., for the estimation of mass discharge or contaminant degradation rates, often is based on point measurements at observation wells. In addition to the problem, that point measurements may not be spatially representative, a further complication may arise due to the temporal dynamics of groundwater flow, which may cause a concentration measurement to be not temporally representative. This paper presents results from a numerical modeling study focusing on temporal variations of the groundwater flow direction. “Measurements” are obtained from point information representing observation wells installed along control planes using different well frequencies and configurations. Results of the scenario simulations show that temporally variable flow conditions can lead to significant temporal fluctuations of the concentration and thus are a substantial source of uncertainty for point measurements. Temporal variation of point concentration measurements may be as high as the average concentration determined, especially near the plume fringe, even when assuming a homogeneous distribution of the hydraulic conductivity. If a heterogeneous hydraulic conductivity field is present, the concentration variability due to a fluctuating groundwater flow direction varies significantly within the control plane and between the different realizations. Determination of contaminant mass fluxes is also influenced by the temporal variability of the concentration measurement, especially for large spacings of the observation wells. Passive dosimeter sampling is found to be appropriate for evaluating the stationarity of contaminant plumes as well as for estimating average concentrations over time when the plume has fully developed. Representative sampling has to be performed over several periods of groundwater flow fluctuation. For the determination of mass fluxes at heterogeneous sites, however, local fluxes, which may vary considerably along a control plane, have to be accounted for. Here, dosimeter sampling in combination with time integrated local water flux measurements can improve mass flux estimates under dynamic flow conditions.