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Health issues related to aquifer contamination with perchlorate are a growing concern in drinking water management. This study describes perchlorate transport and degradation processes from a contaminated stream toward drinking water pumping wells. Investigations are based on laboratory experiments and field measurements conducted at a well field near Bordeaux (France) in a heterogeneous carbonate aquifer interacting with a stream. Field measurements facilitated the characterization of perchlorate contamination and stream-to-aquifer flow. Experiments on columns of streambed sediments conducted in the laboratory confirmed that perchlorate had been degraded in the hyporheic zone. A one-dimensional reactive transport model was implemented to estimate Monod kinetic rates, which account for the inhibition of perchlorate degradation by nitrate. The estimated half-saturation constant for perchlorate $$ \Big({k}_{1/2}^{\mathrm{Pcl}} $$ ) is 6.93 10−9 mol L−1 and the estimated maximum specific degradation rate ( $$ {k}_{\mathrm{max}}^{\mathrm{Pcl}} $$ ) ranges between 10−5 and 4.0 10−3 mol L−1 day−1. Despite degradation in the hyporheic zone, perchlorate-contaminated stream water reaches drinking-water-production units. Such contamination highlights the effects of preferential flow paths between the stream and the pumping wells and significant hydraulic gradients caused by drawdowns. In such contexts, in spite of a good potential for degradation, riverbank filtration may not be effective for the protection of drinking water wells. Lessons from this study also reveal that contamination monitoring can be misleading: low concentrations can be reported in monitoring wells between the contaminant source and the production wells, but the latter may yet be contaminated.

Analytical and numerical models describing the evolution of contaminant concentrations in the plume associated with the dissolution of NAPL source and degradation processes were presented in the literature. At real sites and particularly in complex aquifers like chalk, it is difficult to understand how the sources of contaminants evolve with time. 1,1,1-Trichloroethane (1,1,1-TCA) is one of the few compounds with a well-known hydrolysis constant, that can help to improve knowledge of the contaminant sources and transport rates of dissolved contaminants in groundwater by dating the spill. In this work, different scenarios that could explain the evolution of the concentrations of 1,1,1-TCA and its degradation product 1,1-Dichloroethene (1,1-DCE) at a real contaminated site were investigated by analytical and numerical modelling. The results show that (1) the peaks of concentration time series do not correspond to a single contamination event even in the case of a complex medium, (2) the multiphasic behavior of the concentration time series is dictated by the dissolution in a heterogeneous medium, and (3) the persistence of the concentrations can arise from a small residual organic phase or transport in dual domain medium.

International audience; Soils and groundwater are often contaminated by complex organic mixtures also called Non Aqueous Phase Liquids (NAPLs). Several techniques such as drilling, monitoring of soil gas or injection of tracers are traditionally used to quantify NAPLs in aquifers but are complex to perform. The use of natural soil gas such as 222Rn could be an easy and cheap alternative. This method requires the knowledge of the radon NAPL-water partitioning coefficients (Kn-w.). Once spilled on soil, NAPL will undergo degradation (evaporation, effects of sun light among others) and this degradation could impact the Kn-w. This study aims at investigating the partitioning coefficients of complex NAPLs such as commercial diesel fuel and gasoline in relation to degradation such as evaporation and UV-degradation. For that purpose, batch experiments and GCMS investigations were carried out. The results show different Kn-w for the commercial diesel fuel (60.7 ± 6.1) and gasoline (37.4 ± 5.6). The results also show different Kn-w behaviors in relation with degradation. Degraded diesel fuel display opposite Kn-w values (74.8 ± 7.5 and 25.1 ± 2.5 for UV degraded and evaporated diesel fuel, respectively), compared to fresh one. Degraded gasoline shows no significant variations of the Kn-w compared to fresh one. The molecular investigation reveals the removal of the most volatile fraction for the evaporation treatment, whereas UV-degradation do not have pronounced effects on the chromatogram pattern. For the gasoline molecular investigation, no difference is observed between the treatments excepted a very slight removal of the lightest compounds under evaporation. These results show that NAPL degradation have effects on the Kn-w for diesel fuel and no significant effects for gasoline, at least with these degradation paths. This Kn-w variation will have in fine effects on 222Rn activity interpretation and NAPL subsurface quantification.

In this paper, the behavior of foam in a porous medium is studied in order to understand the effect of the fluid velocity on foam properties. This aspect is crucial during foam injection, as due to radial effects the foam velocity largely decreases around the injection well. The foam properties are detailed through the use of a new local equilibrium foam model parameter estimation approach using an improved new shear function and based on the most widely used STARS model developed by the Computer Modeling Group (CMG). A new mode of calculation of the STARS model parameters is then presented in order to allow both a semiautomated fitting of several quality scan pressure curves and a consideration of the role of the total velocity. The approach is tested through column experiments done at various velocities and gas fractions. Furthermore, the proposed model is also tested on literature results in order to validate it for very different experimental conditions. This study and the fitted results are then used to understand, on both our column experiments and the literature data, the existence of two shear effects and their origins.

Since the fifties, organochlorine pesticides (OCPs) had been used in agriculture to protect vegetables. Two decades after their ban by the Stockholm convention in 2001, OCPs are still present in agricultural soils inducing vegetable contamination with concentrations above Maximum Residue Level (MRL). This is a major concern for a 5 km

Soils and groundwater are often contaminated by complex organic mixtures also called Non Aqueous Phase Liquids (NAPLs). Several techniques such as drilling, monitoring of soil gas or injection of tracers are traditionally used to quantify NAPLs in aquifers but are complex to perform. The use of natural soil gas such as

Large sedimentary basins represent major groundwater resources vital in sustaining terrestrial ecosystems and the various socio-economic activities essential to modern day society (drinking water supply, health, agriculture, energy, and industry). To address the ongoing and future impacts of climate change and anthropogenic activities on groundwater sustainability a better understanding of groundwater storage and flow dynamics in these multi-aquifer systems is crucial. Groundwater ages in this respect serve as an effective tool, providing valuable insight into rates and sources of groundwater recharge and subsurface heterogeneity. In this study we investigated the well-studied Aquitaine Basin located in Southwest France, the 2nd largest sedimentary basin in the country, with an extensive repository of hydrologic and geochemical data spanning several decades. A 3D regional numerical flow model was developed and extended to simulate reactive transport of radiogenic, 14C. An inverse modeling approach using available 14C activity data is implemented to infer groundwater ages and constrain modern and historic recharge sources and aquifer response times. Preliminary findings from spatial variations in 14C concentrations and groundwater ages point to the role of aquitards as important sources of recharge in regional scale, multi-aquifer systems.

International audience; In order to observe the relationships between the temporal variations of CO2 surface fluxes and the CO2 soil gas transport in soil profile before and during rainfall events, two experiments were conducted in a controlled natural environment at different time periods. These experiments consisted in injecting pure CO2 in a lysimeter at 160 cm depth and simulating heavy rainfall event at its surface for 2 weeks. During the whole experiments, CO2 soil gas concentrations and surface fluxes were continuously monitored. These measurements showed that the flux measured through the flux chamber were consistent with the concentration profiles. During simulated rainfall events, the concentrations and fluxes showed a clear change linked to the presence of water on the top of the water profile. The results clearly show a significant decrease of CO2 flux to atmosphere induced by rainfall infiltration and consequential wash-out of the CO2 present in the soil.

Bail-down testing is commonly used to determine the LNAPL transmissivity, volume and initial recovery rate for LNAPL contamination in soil. In this study, a non-compositional three-phase LNAPL/water/air bail-down test model is simulated on the multiphase simulator $$\hbox {DuM}u^x$$ (DUNE for Multiphase, Component, Scale, Physics flow and transport in porous media). Field observation data validate the model. Then, different scenarios were simulated to compare the estimated transmissivity using the modified Bouwer and Rice (Huntley in Groundwater 38:46–52, 2000) approach for different soil properties and fluid viscosity. The results show that (1) estimates are reliable for subsurface layers of variable permeability ranges and yield accurate results for low-permeable soil; (2) estimates are sensitive to the Van Genuchten $$\alpha $$ . Results show poor estimation using low $$\alpha $$ values. Employing the modified Bouwer and Rice approach for bail-down test interpretation at sites where the capillary fringe is thick is not recommended; (3) estimates are sensitive to the initial LNAPL thickness $$h_{n}$$ . Results show that interpretation is not possible if the initial thickness of the contamination is below 1 m for selected parameters; (4) estimates were flawed for low-viscosity fluid and improved as the viscosity of fluid increased; and (5) for scenarios where contamination exists in multilayer soil, the modified Bouwer and Rice approach yields reliable estimates. However, this study tested only one arrangement of this type, wherein the bottom layer consisted of coarse soil.

Foam is to be used as a blocking agent for confining a pollutant source zone and avoid spreading in an aquifer. To this end, it is necessary to determine where injected foam flows and stays inside a porous medium. This study examines the use of electrical resistivity tomography for this purpose. Foam is injected in a large-scale 3D heterogeneous porous medium (0.84 × 0.84 × 0.84 m). During the injection, electrical resistivity tomography measurements are performed. We show that combining a large number of measurements with inversion techniques allows for the monitoring of a foam front in 3D during the injection process.

Managed aquifer recharge (MAR) is increasingly used as a water management tool to enhance water availability and to improve water quality. Until now, however, the risk of fluoride release during MAR with low ionic strength injectate has not been recognised or examined. In this study we analyse and report the mobilisation of fluoride (up to 58 µM) and filterable reactive phosphorus (FRP) (up to 55 µM) during a field groundwater replenishment experiment in which highly treated, deionised wastewater (average TDS 33 mg/L) was injected into a siliciclastic Cretaceous aquifer. In the field experiment, maximum concentrations, which coincided with a rise in pH, exceeded background groundwater concentrations by an average factor of 3.6 for fluoride and 24 for FRP. The combined results from the field experiment, a detailed mineralogical characterisation and geochemical modelling suggested carbonate-rich fluorapatite (CFA: Ca10(PO4)5(CO3,F)F2) to be the most likely source of fluoride and phosphate release. An anoxic batch experiment with powdered CFA-rich nodules sourced from the target aquifer and aqueous solutions of successively decreasing ionic strength closely replicated the field-observed fluoride and phosphate behaviour. Based on the laboratory experiment and geochemical modelling, we hypothesise that the release of fluoride and phosphate results from the incongruent dissolution of CFA and the simultaneous formation of a depleted layer that has hydrated di-basic calcium phosphate (CaHPO4·nH2O) composition at the CFA-water interface. Disequilibrium caused by calcium removal following breakthrough of the deionised injectate triggered the release of fluoride and phosphate. Given the increasing use of highly treated, deionised water for MAR and the ubiquitous presence of CFA and fluorapatite (Ca10(PO4)6F2) in aquifer settings worldwide, the risk of fluoride and phosphate release needs to be considered in the MAR design process.

International audience; The inverse problem of groundwater models is often ill-posed and model parameters are likely to be poorly constrained. Identifiability is improved if diverse data types are used for parameter estimation. However, some models, including detailed solute transport models, are further limited by prohibitive computation times. This often precludes the use of concentration data for parameter estimation, even if those data are available. In the case of surface water-groundwater (SW-GW) models, concentration data can provide SW-GW mixing ratios, which efficiently constrain the estimate of exchange flow, but are rarely used. We propose to reduce computational limits by simulating SW-GW exchange at a sink (well or drain) based on particle tracking under steady state flow conditions. Particle tracking is used to simulate advective transport. A comparison between the particle tracking surrogate model and an advective–dispersive model shows that dispersion can often be neglected when the mixing ratio is computed for a sink, allowing for use of the particle tracking surrogate model. The surrogate model was implemented to solve the inverse problem for a real SW-GW transport problem with heads and concentrations combined in a weighted hybrid objective function. The resulting inversion showed markedly reduced uncertainty in the transmissivity field compared to calibration on head data alone.

In water-scarce areas, the reclamation of wastewater through advanced water treatment and subsequent reinjection into depleted aquifers is an increasingly attractive water management option. However, such injection can trigger a range of water-sediment interactions which need to be well understood and quantified to ensure sustainable operations. In this study, reactive transport modeling was used to analyze and quantify the interacting hydrogeochemical processes controlling the mobilization of fluoride and phosphate during injection of highly treated recycled water into a siliciclastic aquifer. The reactive transport model explained the field-observed fluoride and phosphate transport behavior as a result of the incongruent dissolution of carbonate-rich fluorapatite where (i) a rapid proton exchange reaction primarily released fluoride and calcium, and (ii) equilibrium with a mineral-water interface layer of hydrated dibasic calcium phosphate released phosphate. The modeling results illustrated that net exchange of calcium on cation exchange sites in the sediments postbreakthrough of the injectant was responsible for incongruent mineral dissolution and the associated fluoride and phosphate release. Accordingly, amending calcium chloride into the injectant could potentially reduce fluoride and phosphate mobilization at the study site. Insights from this study are broadly applicable to understanding and preventing geogenic fluoride mobilization from fluoride-bearing apatite minerals in many other aquifers worldwide.

International audience; Foams can be used to remediate aquifer pollution due to industrial leaks. However, when in contact with oily pollutants, foams may collapse and thus have a very limited life-time. A suitable formulation of biodegradable foam that resists oil contact is therefore needed. Hence, the ability of xanthan polymer and silica colloidal particles to stabilise foam against oil was investigated. Their performance in terms of stabilisation was evaluated via foam generation experiments in columns of porous medium, conducted with and without oil. The results show that the addition of xanthan polymer led to an increase in the viscosity of the solution, which thwarted the formation of foam. It did not improve the resistance of foam to oil, but increased altogether the resistance factor up to more than twice the original value. Concerning silica particles, it was demonstrated that they both noticeably increased resistance factor and moderately stabilised foam against oil by 20% at optimum concentration. As such, this study presents a new way to reinforce foam against oil for soil remediation issues.

Several remediation techniques are available to treat source zones with Non-Aqueous Phase Liquids (NAPLs). Despite hundreds of treated sites, it is still quite difficult to estimate the potential efficiency of a treatment technique under a given context. In the literature, numerous papers deal with the potential limitations of one remediation technique at a laboratory scale or in the field, but only a few studies compared two or more different techniques. Thus, the objective of this chapter is to compare different treatment techniques in the same solid matrix and under the same conditions at three different experimental scales: batch, columns, and metric pilot tank experiments. The chosen techniques are among the most common ones, i.e., oxidation, sparging, surfactant flushing, and low-temperature thermal treatment. These four techniques were applied first at the batch and column scale in order to assess their potential efficiency under well-controlled conditions. These experiments are mandatory for choosing the best oxidant, the activating agents for this oxidant, the best concentration, and the determination of the limiting factors which can be encountered. All these lab experiments allowed a selection of favorable conditions for testing four techniques at the pilot scale. These treatment techniques were tested in the same configuration, in tanks of one cubic meter volume, filled with sand and emplaced sources containing a toluene/decane mixture as representative of a NAPL phase. The major findings of this study are: (1) Thermal treatment was the most efficient remediation technique; (2) Dissolution issues reduced the efficiency of the three other techniques; (3) Heterogeneity in the tanks caused a decrease in the removal efficiency for all treatments compared to efficiencies obtained at the column scale; (4) Density effects, which were not encountered at the column scale, caused problems for oxidant injection in the tanks; (5) Removal techniques that are equal for mass-based removal goal were quite different in lowering the dissolved contaminant flux from the system. Therefore, the ranking of techniques based on mass removal may not be appropriate and be replaced by a flux reduction selection; and (6) A need to perform experiments at three experimental scales is evidenced: batch studies allow sufficient variations in experimental conditions, the column experiments permitted the optimization of surfactant and oxidant injection, whereas tank experiments allow studies under heterogeneous flow conditions.

International audience; The potential of LNAPL delineation by 222Rn soil-gas monitoring in a chemically heterogeneous vadose zone was investigated in this study based on laboratory (batch and columns) experiments and numerical modelling. An enhanced version of the MIN3P reactive transport code was used to simulate Rn transport in both uncontaminated and NAPL-contaminated vadose zones and results were validated against analytical solutions and laboratory experiments. Results show that 222Rn activity profiles are mainly controlled by porous media 222Rn production, vadose zone fluid saturations and especially the type and distribution of NAPL in contaminated areas. The results also show that decreases in 222Rn activity and variations in activity gradients provide evidence for the presence and saturation of NAPL. This study demonstrates that LNAPL delineation via 222Rn gas surveys at contaminated sites works best, if gas measurements extend as deep as possible and include regions where 222Rn activity decreases due to elevated NAPL content. In addition, collection and analysis of depth-discrete gas samples allows the characterization of vertical NAPL distribution based on the 222Rn activity gradient. The determination of 222Rn production in the unsaturated zone, as well as water capillary pressure curves are of key importance in enabling the discrimination of an uncontaminated from a NAPL-contaminated area.

In situ remediation techniques for groundwater pollution are quite diverse. However, the success of these is often random. The first part of the article will focus, from a literature review and some examples, to determine the parameters that unfortunately lead to a low efficacy of treatment. This point will be supplemented by an analysis of the feedback on treatments at the pilot scale. The limits are generally related to the heterogeneity of the geological formations but also to a poor targeting of the laboratory analyses or to a poor monitoring of the rehabilitation. In a second part we will examine recent progress to maximize the effectiveness of in situ treatments. At first, we emphasize diagnostic techniques that make it possible to target the flow of pollutants. Following a general presentation of innovative techniques, we will particularly present an original technique : the injection of foam to block the porosity of around a source area. Les techniques de réhabilitation in situ des pollutions en nappes souterraines (source ou panache) sont très variées. Cependant le succès de celles-ci est souvent aléatoire. La première partie de la présentation s’attachera, à partir d’une revue bibliographique et de quelques exemples, à déterminer les paramètres qui conduisent souvent à une faible efficacité du traitement. Ce point sera complété d’une analyse du retour d’expérience sur des pilotes de traitement. Les limites sont généralement liées à l’hétérogénéité des formations géologiques mais aussi à un mauvais ciblage des analyses préparatoires ou à des faiblesses dans le suivi de la réhabilitation. Dans une deuxième partie nous examinerons les progrès récents visant à maximiser l’efficacité des traitements in situ. En premier lieu il s’agit de techniques de diagnostic qui permettent de cibler les flux de polluants. Et dans le cadre des techniques innovantes, nous présenterons particulièrement une technique originale : l’injection de mousse permettant de bloquer la porosité du milieu autour d’une zone source.

Intrinsic molecular parameters (solubility, chemical structure, etc.) as well as physico-chemical properties of the medium (lithology, permeability, organic matter content, etc.) and hydrological specificities (rainfall regimes) are usually put forward to characterize the mobility of polycyclic aromatic hydrocarbons (PAHs). Here, we study the role of aggregate mechanical redesigning on the ability of anciently impacted soils to release polycyclic hydrocarbons. Soil columns were collected in a heavily impacted wasteland (Villeneuve la Garenne, France) for this purpose and submitted to continuous and sequential leaching regimes. The soil’s organo-mineral properties were characterized with suited techniques (Rock Eval, FT/IR) prior to the leaching experiments. The release of 18 PAHs (naphthalene, 1 methyl naphthalene, 2 methyl naphthalene, acenaphtylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benz(b)fluoranthene, benz(k)fluoranthene; benzo(a)pyrene, indeno[1,2,3-cd]pyrene, dibenz(a,h)anthracene, benzo(g,h,i) perylene) was assayed under non-disturbed configuration of the columns, then under reshuffled (10 mm), and finely sieved (4 mm) states in order to evaluate the impact of grain redistribution on the mobilization of the aromatic molecules. For both sequential and continuous leaching regimes, results showed a substantial increase of released amounts when the systems were disturbed. Significant increases of PAH concentrations were indeed observed when the columns were reshuffled (10 mm). The release was more intense when the mechanical reworking was performed with a smaller threshold (4 mm). Greater accessibility of the molecules drove very likely PAH release during the mechanical reworking operations.

The potential of LNAPL delineation by

Foam can be used to achieve environmental remediation in case of contamination caused by light non aqueous phase spills. However, when it comes in contact with oily pollutants, foam becomes weaker and its life time is greatly reduced. Such weakening can be dampened by using silica particles -together with saponin surfactant- which were shown to reinforce foam in bulk and 1D sandpack experiments. Here is addressed both foam propagation in a 2D porous media when buoyancy and gravity interfere, and foam behaviour when in contact with floating oil. Therefore, macroscopic foam displacement, and specific liquid and gas phases behaviours were studied in a 2D-tank. A piston-like displacement was observed during foam propagation in the absence of oil, while foam liquid phase was influenced by gravity and did not propagate homogeneously on entire tank height. In the presence of oil, foam was partly destroyed, which increased the local permeability of gas and created new preferential paths for gas flow. This effect was partially avoided via a surfactant concentration increase, but solid colloidal particles turned out to be a more efficient stabilizing agent, by significantly increasing foam strength and its oil-tolerance.

This paper presents a comparison of hydraulic oil conductivity obtained from interpreting bail-down test data to values calculated from theory. The bail-down tests were performed at laboratory scale, on a radial portion of a circular domain filled with calibrated sand allowing hydraulic oil conductivity to be calculated using Parker’s theoretical model (Parker et al. in Water Resour Res 23(4):618–624, 1987). The bail-down tests were interpreted using the modified Bouwer and Rice (Huntley in Ground Water 38(1):46–52, 2000) and the modified Cooper methods (Beckett and Lyverse in API Interact LNAPL Guide 2:1–27, 2002). The results show that (1) both interpretation methods from bail-down test data give similar hydraulic oil conductivities, and (2) the hydraulic oil conductivities estimated from bail-down test data agree well with the hydraulic oil conductivity predicted when using the Parker theoretical model. Overall, this paper confirms that the modified Bouwer and Rice (Huntley 2000) and the modified Cooper methods (Beckett and Lyverse 2002) are valid to estimate hydraulic oil conductivity, giving realistic values despite test conditions not meeting all the assumptions and boundary conditions of each analytical solution.

This paper evaluates the results from three methods commonly used to estimate oil transmissivity: the modified Cooper solution (Beckett and Lyverse 2002), the modified Bouwer and Rice method (Kirkman 2013), and the modified Jacob and Lohman method (Huntley 2000). Determining the validity of oil transmissivity values is important (e.g., when used in extraction system design and operation) and not straightforward as these methods are based on different assumptions and boundary conditions and introduce different simplifying assumptions to allow for estimating oil drawdown. Data from 289 bail-down tests performed during an oil remediation project were used in this evaluation. Analysis of these tests produced realistic transmissivity values and good correlation between these three methods, giving the authors confidence in the oil transmissivity values as this correlation is reflected across a significant number of data sets. Secondly, the nature of oil and water recharge to the wells interpreted from Kirkman's J-ratio values largely validates the Huntley (2000) simplifying assumption that the potentiometric surface will be relatively constant during the test, allowing the use of the modified Bouwer and Rice method. Finally, the impact of oil extraction on measured oil thickness and estimated oil transmissivity was also assessed. The study showed a clear general decrease in both measured oil thicknesses and estimated oil transmissivity during the oil recovery project. However, measured oil thickness and estimated oil transmissivity are not clearly correlated, and, as a consequence, the range of decrease in one parameter does not allow any prediction of the range of decrease in the second parameter.

Over more than a century of intense industrial production and associated accidental release, petroleum products (e.g., gasoline, diesel, fuel oil) have contaminated a significant portion of the world's groundwater resources. Groundwater remediation is generally a complex task, especially where aquifers and the associated contaminant distribution are highly heterogeneous. The ability to predict the efficiency of such remediation is of crucial importance, as the costs are strongly linked to the treatment design and duration. In this study, a coupled simulation-optimization (S/O) framework, consisting of a process-based reactive transport simulation model linked with particle swarm optimization (PSO) was developed. It was subsequently applied for the design of a real-world in situ bio-treatment of a BTEX contaminated aquifer in France. In the application, the optimization framework was used to simultaneously determine optimal well locations and their optimal injection rates, both constituting key elements of the enhanced biodegradation design problem. The optimization of the treatment efficiency was examined in terms of three different regulatory objectives, (1) minimization of the residual NAPL mass of the key contaminant, i.e., benzene, in the source zone, (2) reduction of the maximum concentration of benzene in groundwater, and (3) minimization of the time required to reduce the benzene concentration in groundwater to below a threshold value. Our analysis of potential, optimal remediation strategies showed that: (i) the complexity of the biodegradation behavior at real sites may favor very different remediation options as a result of varying remediation targets, (ii) the long term behavior of the contaminants after the end of the active treatment period, which is often neglected, showed to have a significant influence on remediation design that requires increased attention, (iii) PSO has shown to be a very efficient algorithm in the context of the present study. The insights that can be gained from such a framework will provide decision support to select the most suitable remediation strategy while facing different regulatory objectives.

An innovative solution for groundwater velocity measurement in wells, the Direct Velocity Tool (DVT), is developed and tested. The DVT allows measurement of Darcy flux at centimeter scale vertical resolution requiring only a few minutes for each measurement (typically 5–10 min). Results are generated in real time through the use of an equation. The theoretical functional Darcy flux range is between 1 and 40 cm.day−1 for an aquifer with a hydraulic conductivity, K, less than 10−3 m.s−1. Laboratory tests showed a linear response between Darcy flux imposed and Darcy flux measured with the DVT, with a high correlation coefficient (R2 = 0.99). The DVT was tested for velocities ranging from 5 to 30 cm.day−1 where a higher standard deviation was observed for higher velocity (±6.46 cm.day−1 for 30 cm.day−1). At a hydraulically controlled field site, tracer tests, borehole dilutions, Passive Flux Meter (PFM) and DVT were tested under constant flow conditions. The PFM, tracer test and DVT technologies measured similar Darcy flux ranging from 10 to 17 cm.day−1. The DVT and PFM had uncertainties of 2.70 cm.day−1 and 2.50 cm.day−1, respectively. At a contaminated field site, velocities measured with the PFM range between 5 and 9 cm.day−1, while the DVT provided velocities of 4 to 8 cm.day−1. Velocity measurement showed similar results at the contaminated field site between PFM and DVT. The DVT offers an innovative solution for Darcy flux measurement and can be deployed easily. It provides the capability to characterize the vertical distribution of the horizontal velocity for a well in a period of 1–2 h. Keywords: Direct velocity tool, Darcy flux measurement, Laboratory and field comparison, Innovative

Development of organisms that live on contaminated soils depends on toxicity as well as several physical and chemical soil properties. We aimed to identify plant bioassays most responsive to contaminants and not to confounding factors due to soil type differences. We implemented a multi-site approach in seven contaminated sites and used different ordinary plant bioassays (fourteen-day-shoot biomass and five-day-root and shoot elongation). Most of the sites were contaminated with polycyclic aromatic hydrocarbons (PAHs), and soils were sampled from areas of both high and low contamination. Bioassays were performed on ninety soil samples and were carried out with six model species. We performed analyses of regulatory PAHs and their derivatives content in the samples. Fourteen-day-shoot biomass responses depended on the site's origin, with an intricate response of plants that faced contrasted soil pH and organic matter content and various contaminant levels. Five-day-shoot and root lengths were informative when considering the most heavily PAH-contaminated site, since both measures exhibited a close dose-dependent response to PAHs but not to soil pH or organic matter content. For the other sites, elongation tests revealed tenuous effects somehow related to the presence of PAHs or their derivatives. We propose that tests based on plant development during their autotrophic phase (the fourteen-day-shoot biomass test in this study) are likely more sensitive to environmental stressors but less specific for contaminant-induced effects. Comparatively, tests based on early and heterotrophic plant development could be particularly more specific for soil contaminants, but the associated responses may be of low sensitivity.

Foam injection is widely used in petroleum industry for enhanced oil recovery, but has received limited attention for the application of environmental remediation at the field scale. This study analyses the use of foam as a blocking agent, i.e. to confine a source zone of contaminant in groundwater. Laboratory experiments in 1D porous media with a commercially available biodegradable surfactant performed on columns using pre-generated foam show that the foam reduces the relative water permeability $$k_{\mathrm {rw}}$$ by a factor of 100–1000. $$k_{\mathrm {rw}}$$ was measured right after foam placement by injecting only water (drainage test) and corresponding to the relative permeability of water in presence of foam. A comparison to a theoretical two-phase flow in porous medium shows that the Van Genuchten equation can be used to estimate the $$k_{\mathrm {rw}}$$ value. In the field, experiments done on two different porous media and using three different injection techniques (co-injection, surfactant alternating gas, pre-generation) show a clear confining ability of the produced foam. A $$k_{\mathrm {rw}}$$ reduction by a factor of 1000 is observed very close to the well and close to 100 at 1 m of this well. These values were obtained with a much weaker foam than the laboratory one in order to allow the injection at shallow depth environmental compatible ssure ( $$\le $$ 4 bar). The reduction in water relative permeability can occur in the presence of a foam that does not cause an extreme reduction of the mobility, indicating that this reduction does not depend on resistance factor (RF) values. There is potential for improvement of the foam as it loses its efficiency with increasing distance from the injection well.

The injection of steam is a well-established technique for the thermally enhanced remediation of both unsaturated and saturated soils. Under saturated conditions, there is a limitation related to the thermal radius of influence (TRI) which results from the balance between viscous forces due to injection and buoyant forces due to the density difference between steam and water. Targeted preheating of the soil reduces the required time for a gaseous (steam) flow to be established after the beginning of a steam injection into the soil. Compared to non-preheated zones, the region where steam exists reaches a larger lateral extent before buoyancy eventually leads to a vertical breakthrough of the steam. This study investigates the impacts of preheating on the thermal radius of influence by considering different preheating scenarios with a full-complexity, 3D, non-isothermal numerical model including phase change. The achievable benefits of preheating are discussed; the potential costs of preheating are also considered. It is shown that preheating increases the TRI by more than 10 %. This is not much, but it suggests that preheating is an interesting option in cases where the increased TRI leads to a reduced number of injection wells required.

Contamination of soil and groundwater with nonaqueous phase liquid represents a major environmental concern because of the negative effect on human health. Traditional soil flushing techniques have been proved ineffective in heterogeneous aquifers, since liquids for remediation flow preferentially through the most permeable layers and residual oil remains trapped in the low-permeability sediments. To improve the sweep efficiency, fluids with lower mobility than resident liquids can be injected, such as polymers or in situ generated foam. In addition, foam has the potential of selectively reducing mobility in higher-permeability layers compared to lower-permeability layers. The use of foams has not been popular because foam mobility is difficult to predict. In this paper, a series of 1D column experiments were conducted to investigate the variation of the resistance factor RF as a function of the permeability. Five types of sand and calibrated glass beads were used to obtain porous media of permeabilities ranging from 250 millidarcy to 100 Darcy. Two commercial nonionic surfactants, \(\hbox {Triton}^{{\circledR }}\) X-100 (commonly used but toxic) and sucrose laurate (environmentally friendly surfactant, biodegradable), were used at a concentration equal to 10 critical micelle concentration. Columns were first saturated with water and then flushed with 1.5 PV (pore volumes) of surfactant solution in order to achieve the adsorption of molecules into the soil matrix. Then, co-injection of air and surfactant solution was performed at a constant total rate to generate in situ foam. The quality of the foam was varied from 85 to 99 % to investigate the effect of this parameter on the resistance factor. A graphic showing the dependence of RF and the permeability is presented. Results suggest that for the same total flow rate, the RF decreases as permeability increases, but for permeabilities smaller than 1 Darcy, the RF is weak, probably due to the difficulty to generate stable foam under high capillary pressures. Variations in foam quality and surfactant type do not seem to have an important effect on the results regarding RF. The presented results are assistance for predicting foam behavior in porous media of different permeabilities.

Qualité des Milieux Naturels

A novel approach using foam to manage hazardous waste was successfully demonstrated under active site conditions. The purpose of the foam was to divert groundwater flow, that would normally enter the source zone area, to reduce dissolved contaminant release to the aquifer . During the demonstration, foam was pre generated and directly injected surrounding the chlorinated solvent source zone. Despite the constraints related to the industrial activities and non-optimal position of the injection points, the applicability and effectiveness of the approach have been highlighted using multiple metrics. A combination of measurements and modelling allowed definition of the foam extent surrounding each injection point, and this appears to be the critical metric to define the success of the foam injection approach. Information on the transport of chlorinated solvents in groundwater showed a decrease of contaminant flux by a factor of 4.4 downstream of the confined area. The effective permeability reduction was maintained over a period of three months. The successful containment provides evidence for consideration of the use of foam to improve traditional flushing techniques, by increasing the targeting of contaminants by remedial agents.

In this paper we present an experimental study of foam flow in porous media dealing with 1D sandpacks columns and 2D laboratory pilot. 1D porous column were dedicated to the study of foam generation and propagation in porous media of different permeabilities. We show that the resistance factor (RF) to flow, that is the ratio between pressure drop in presence of foam and pressure drop in absence of foam, is a non-monotonous function of permeability. A 2D transparent laboratory pilot (1 × 0.5 × 0.02 m3), made of two water saturated sand layers of different permeabilities has been used to visualize foam flow. We clearly see that foam remains in high permeability layer and does not enter in the low permeability one. Moreover when we inject a liquid tracer we see that fluid velocities are quite similar in both layers showing the front straightened up.

In this paper, four treatment techniques commonly applied to Volatile Organic Compounds (VOC) removal from soil are compared in column experiments with pure sand containing a residual Light Non-Aqueous Phase Liquid (L-NAPL) contamination. Oxidation is tested through the injection of Fenton reagent, with persulfate, and combined with sparging with the injection of ozone. Surfactant treatment was conducted at low flow rates with Tween®80. Sparging was conducted by air injection but at a low flow rate of 1 mL min−1. Finally several columns were thermally treated at a temperature of 80 °C. The results showed high removal (>90%) for all techniques used, although only thermal treatment on BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) reached 100% efficiency. The main limiting factors of each technique were: (i) for oxidation, the solubility of the substance limited the removal; (ii) for surfactant both the solubility in the surfactant and the type of surfactant are important; (iii) for sparging, the main factors are contaminant vapor pressure and porous media grain size; (iv) for thermal treatment, the limitation arises from the contaminant vapor pressure and the medium hydraulic conductivity. A comparison with literature data shows that the results are consistent with most of the studies conducted on one technique.

A contaminant source localisation strategy was developed considering unknown heterogeneous hydraulic conductivity field, unknown dispersivity and unknown location of a continuous contaminant source. The Gauss-Levenberg-Marquardt algorithm is combined with a data worth analysis to estimate the unknown parameters and identify the best locations of additional measurements. The data collection strategy is iterative, based on the ability of the additional dataset to decrease the uncertainties on the contaminant source location. Two 2D synthetic models are considered. The method is first illustrated with a simple model and a more complex model is then considered to evaluate the ability of the approach to locate the contaminant source from hydraulic heads and concentration data. This approach is parsimonious in terms of model runs and applicable to real cases. The results give a good estimate of the source location and the dispersivity, with acceptable NRMSE for each case. New observations introduced at each iteration decrease the standard deviation of the source location and improve the NRMSE. The estimated hydraulic conductivity field presents the same features as the original field.

Soil flushing using aqueous solutions is employed to solubilise contaminants. As water solubility is the controlling mechanism of dissolution, additives (surfactants, cosolvents, etc.) are used to enhance efficiencies and reduce the treatment time compared to the use of water alone. The use of surfactant alone gives efficiencies of about 80–85 % in laboratory experiments, but the amounts of product to be injected are very important, which does not seem to be economically sustainable. Studies indicate that when soil flushing is applied in the field, efficiency is very variable; it can vary from almost 0 % to almost 100 %. This illustrates the importance of knowledge of the field (soil heterogeneities, type of contamination, etc.). Using only one product (surfactant, cosolvent, cyclodextrin) often gives moderate efficiencies and needs very large amounts of products, with a product:pollutant ratio higher than 100:1. On the other hand, the use of more complex methods involving micro emulsions or several products with polymer injection lead to high efficiencies at first and a product:pollutant ratio that can be lower than 5. The importance of the initial saturation of the non-aqueous phase liquid is highlighted: the higher the initial saturation, the higher the efficiency. For initial saturations lower than 1 %, soil flushing may not be a very efficient technique. This paper provides an overview of recent studies in the area of soil and groundwater remediation, from laboratory columns scale to pilot and real sites. The research has focused on chlorinated solvents as they are extremely difficult to treat.

A borehole is developed in a shallow multi-layered aquifer and used to derive the porosity, specific storage and hydraulic conductivity of the aquitard. Local values of hydrodynamical parameters are estimated from petrophysical analysis of core samples, and the empirical relationship between porosity and permeability. Vertical diffusivity is determined from the response of the aquitard to a loading cyclic signal using pressure records at different depths. Hydraulic conductivities deduced from the petrophysical analysis ranged from 10−8 to 10−10 m s−1 and are comparable with those of facies of marine/lacustrine clay observed in samples. The permeability values calculated based on diffusivity are within the range 10−9 to 10−11 m s−1 with a quasi-systematic bias of one order of magnitude. These values are average for a larger part of the aquitard and correspond to an integrated value. The methodology retained for the aquitard characterization is discussed with emphasis on the implications for the ma...

International audience; This study compared four treatment techniques for the removal of a toluene/n-decane as NAPL (Non Aqueous Phase Liquid) phase mixture in identical 1 cubic meter tanks filled with different kind of sand. These four treatment techniques were: oxidation with persulfate, surfactant washing with Tween80®, sparging with air followed by ozone, and thermal treatment at 80 °C. The sources were made with three lenses of 26 × 26 × 6.5 cm, one having a hydraulic conductivity similar to the whole tank and the two others a value 10 times smaller. The four techniques were studied after conditioning the tanks with tap water during approximately 80 days. The persulfate treatment tests showed average removal of the contaminants but significant flux decrease if density effects are considered. Surfactant flushing did not show a highly significant increase of the flux of toluene but allowed an increased removal rate that could lead to an almost complete removal with longer treatment time. Sparging removed a significant amount but suggest that air was passing through localized gas channels and that the removal was stagnating after removing half of the contamination. Thermal treatment reached 100% removal after the target temperature of 80 °C was kept during more than 10 d. The experiments emphasized the generation of a high-spatial heterogeneity in NAPL content. For all the treatments the overall removal was similar for both n-decane and toluene, suggesting that toluene was removed rapidly and n-decane more slowly in some zones, while no removal existed in other zones. The oxidation and surfactant results were also analyzed for the relation between contaminant fluxes at the outlet and mass removal. For the first time, this approach clearly allowed the differentiation of the treatments. As a conclusion, experiments showed that the most important differences between the tested treatment techniques were not the global mass removal rates but the time required to reach 99% decrease in the contaminant fluxes, which were different for each technique.; This study compared four treatment techniques for the removal of a toluene/n-decane as NAPL (Non Aqueous Phase Liquid) phase mixture in identical 1 cubic meter tanks filled with different kind of sand. These four treatment techniques were: oxidation with persulfate, surfactant washing with Tween80®, sparging with air followed by ozone, and thermal treatment at 80 °C. The sources were made with three lenses of 26 × 26 × 6.5 cm, one having a hydraulic conductivity similar to the whole tank and the two others a value 10 times smaller. The four techniques were studied after conditioning the tanks with tap water during approximately 80 days.The persulfate treatment tests showed average removal of the contaminants but significant flux decrease if density effects are considered. Surfactant flushing did not show a highly significant increase of the flux of toluene but allowed an increased removal rate that could lead to an almost complete removal with longer treatment time. Sparging removed a significant amount but suggests that air was passing through localized gas channels and that the removal was stagnating after removing half of the contamination. Thermal treatment reached 100% removal after the target temperature of 80 °C was kept during more than 10 d.The experiments emphasized the generation of a high-spatial heterogeneity in NAPL content. For all the treatments the overall removal was similar for both n-decane and toluene, suggesting that toluene was removed rapidly and n-decane more slowly in some zones, while no removal existed in other zones.The oxidation and surfactant results were also analyzed for the relation between contaminant fluxes at the outlet and mass removal. For the first time, this approach clearly allowed the differentiation of the treatments. As a conclusion, experiments showed that the most important differences between the tested treatment techniques were not the global mass removal rates but the time required to reach 99% decrease in the contaminant fluxes, which were different for each technique.

This article presents field tests comparing two methods of treatment of chlorinated solvents undertaken at the same site. The site is an automobile factory where two chlorinated solvents (CS) plumes were identified. At the first source, in situ chemical reduction (ISCR) was applied, while at the second one, enhanced natural attenuation (ENA) was used. A set of specific multilevel sampling wells were installed approximately 20 m downgradient of the sources to estimate the efficiency of the treatments. The presence of a low-permeability layer (source 1) or a thick oil lens (source 2) in the top part of the aquifer prevented the CS from reaching the bottom of the aquifer. These layers led to difficulties treating the contamination. At the ISCR and ENA treatment zones, the concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) did not change significantly, while the concentration of metabolites (cis-1,2-DCE, vinyl chloride, and ethene) significantly increased 50 to 150 days after treatment. Due to high concentration of CS in the source zone, a mass balance calculation, including chlorine, was possible. It showed that around 1 to 2 percent of the injected products were used to reduce the CS. A detailed analysis and 1D analytical modeling of CS concentrations showed that the treatment led to a large (two to three times) increase in dissolution of the organic phase. This explains why, despite an efficient treatment, the PCE and TCE concentrations remained virtually unchanged. Degradation rates also increased due to the treatment. Due to some differences in the source-zone chemistry, it was not possible to differentiate between the ISCR and ENA efficiencies. © 2013 Wiley Periodicals, Inc.

Organic pollutants such as solvents or petroleum products are widespread contaminants in soil and groundwater systems. In-situ bioremediation is a commonly used remediation technology to clean up the subsurface to eliminate the risks of toxic substances to reach potential receptors in surface waters or drinking water wells. This study discusses the development of a subsurface model to analyse the performance of an actively operating field-scale enhanced bioremediation scheme. The study site was affected by a mixed toluene, dihydromyrcenol (DHM), methanol, and i-propanol plume. A high-resolution, time-series of data was used to constrain the model development and calibration. The analysis shows that the observed failure of the treatment system is linked to an inefficient oxygen injection pattern. Moreover, the model simulations also suggest that additional contaminant spillages have occurred in 2012. Those additional spillages and their associated additional oxygen demand resulted in a significant increase in contaminant fluxes that remained untreated. The study emphasises the important role that reactive transport modelling can play in data analyses and for enhancing remediation efficiency.

International audience; Source delineation of hydrocarbon contaminated sites is of high importance for remediation work. However, traditional methods like soil core extraction and analysis or recent Membrane Interface Probe methods are time consuming and costly. Therefore, the development of an in situ method based on soil gas analysis can be interesting. This includes the direct measurement of volatile organic compounds (VOCs) in soil gas taken from gas probes using a PID (Photo Ionization Detector) and the analysis of other soil gases related to VOC degradation distribution (CH4, O-2, CO2) or related to presence of Light Non-Aqueous Phase Liquid (LNAPL) as Rn-222. However, in widespread heterogeneous formations, delineation by gas measurements becomes more challenging. The objective of this study is twofold: (i) to analyse the potential of several in situ gas measurement techniques in comparison to soil coring for LNAPL source delineation at a heterogeneous contaminated site where the techniques might be limited by a low diffusion potential linked to the presence of fine sands and silts, and (ii) to analyse the effect of vertical sediment heterogeneities on the performance of these gas measurement methods. Thus, five types of gases were analysed: VOCs, their three related degradation products O-2, CO2 and CH4 and Rn-222. Gas measurements were compared to independent LNAPL analysis by coring. This work was conducted at an old industrial site frequently contaminated by a Diesel-Fuel mixture located in a heterogeneous fine-grained aquifer. Results show that in such heterogeneous media migration of reactive gases like VOCs occurs only across small distances and the VOC concentrations sampled with gas probes are mainly related to local conditions rather than the presence of LNAPL below the gas probe. Rn-222 is not well correlated with LNAPL because of sediment heterogeneity. Oxygen, CO2, and especially CH4, have larger lengths of diffusion and give the clearest picture for LNAPL presence at this site even when the gas probe is somewhat distant. (C) 2016 Elsevier B.V. All rights reserved.

A new method to calculate the transport of dissolved species in aquifers is presented. This approach is an extension of the stream tubes which are used for flow computation. The flux tubes defined here are conservative for solutes, but not for water mass. The flux tubes are first defined in a general domain and then calculated in a two-dimensional uniform flow field. The tubes’ computation is based on a parametric solution. The method is extended further in order to deal with heterogeneous media. A particle-tracking algorithm is used where the deviation of the flux-tube boundaries due to dispersion is accounted for. The approximate solution obtained by this approach is compared to classical numerical solutions given by a finite difference code (RT3D) and a finite element code (FEFLOW). This comparison was performed for several test cases with increasing complexity. The differences between the flux-tube approach and the other methods always remain small, even regarding mass conservation. The major advantage of the flux-tube approach is the ability to reach a solution quickly, as the method is hundreds to thousands of times faster than classical finite difference or finite element models.

In this comment, we revisit equations concerning the analytical solutions presented by Gutierrez-Neri and co-workers for reactive transport for a pollutant undergoing core and fringe degradations. We state that a correction needs to be made in Eq. (9) of the work of Gutierrez- Neri et al. in order that the equation follows closely previous work published by J. Bear (in 1-D) and P.A. Domenico (in 3-D). Furthermore we derive alternative solutions for Eqs. (13)–(16) which separate more clearly the first-order reaction and the instantaneous reaction. It is shown that the corrected solution agrees better with the results from the numerical model than the previous solution. An improvement is also made by giving a solution which avoids negative concentrations. Furthermore, the corresponding solution for the electron acceptor reacting with the pollutant is given.