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International audience; The remediation of a polluted site relies, as a first stage, on the proper delineation of the contamination sources. In classical investigations, soil and water samples are collected throughout the field. These measurements allow a quantitative characterization of the gathered materials but only provide information about the medium in the vicinity of the points where they were collected. On the other hand, geophysical techniques can provide a quasi-continuous coverage of the investigated field. This paper describes a geophysical survey that was performed on an industrial site impacted by a chlorinated DNAPL. The precise location of the contamination was needed for the treatment of the saturated zone, while the unsaturated zone was remediated by general excavation of the sediments, followed by separate treatment. As this excavation allowed to get closer to the saturated zone, geophysical measurements were conducted at the bottom of the pit. Whereas Electrical Resistivity Tomography measurements only brought little information, Ground Penetrating Radar drew the remediation operations towards an area that preliminary point measurements had not identified as a possible source location.

Foam propagation and stability in highly permeable porous media , encountered in soil pollution applications, are still challenging. Here, we investigated the application of foam for blocking the aquifer to divert the flow from a contaminated zone and, therefore, ease the remediation treatments. The main aim was to better understand the critical parameters when the foam is injected into a highly permeable aquifer with high groundwater flow velocity (up to 10 m/day). A decimetric-scale 2D tank experimental setup filled with 1 mm glass beads was used. The front part of the 2D tank was made of transparent glass to photograph the foam flow using the light-reflected method. The water flow was generated horizontally through injection and pumping points on the sides of the tank. The pre-generated foam was injected at the bottom center of the tank. Water streamlines (using dye tracing) and water saturation were investigated using image interpretation. Results show that 100% of the water flow was diverted during the injection of the foam. Foam stability in porous media depends significantly on the horizontal water flow rate. Recirculating water containing the surfactant increases foam stability. The main mechanism of destruction was identified as the dilution of the surfactant in water. However, the head-loss measurements showed that despite foam destruction, the relative permeability of the water phase in the media remained quite low. Injection of foam increases the radius of gas propagation, thanks to foam's high viscosity, compared to a pure gas injection case. These results are new highlights on the efficiency of foam as a blocking agent, showing that it can also serve as a means for gas transport more efficiently in porous media, especially for soil remediation applications.

In the management of radionuclide release in the environment, the unsaturated zone could be a natural barrier to delay or to stop the radionuclide migration through the environment and to protect the groundwater from radiological risks. Thus, a suitable scientific evaluation of any radionuclide transport problems related to groundwater may to take into account the processes affecting flow through the unsaturated zone. In this work, an approach that involves the interactions between unsaturated zone and saturated zone both from hydrogeological and radionuclide transport point of view is proposed. This approach was tested developing a case study on an Italian nuclear site. The behavior of unsaturated zone as protective barrier for the groundwater was highlighted and identified as a fundamental aspect in the development of environmental analysis concerning the radionuclide transport into the environment. Promising results were found to improve the design of a radiological monitoring network.

The Propopis tamarugo Phil, also known as Tamarugo, is an endemic and protected tree that survives in the Atacama Desert&mdash, a hyper arid and highly saline environment. The Tamarugo is threatened because of groundwater overexploitation, and its preservation depends on the soil moisture in the vadose zone, as many of the tree roots do not reach the current water table levels. To improve the estimation of soil moisture available for the Tamarugo trees, we applied a hydrogeological model that couples the unsaturated and saturated zones. The model was used to represent different groundwater exploitation and recharge scenarios between February 2006 and September 2030 to predict simultaneously groundwater levels and soil moisture. The model results show that even at locations where water table depletion is relatively small (~1&ndash, 1.5 m), soil moisture can drastically decrease (0.25&ndash, 0.30 m3/m3). Therefore, Tamarugo survival can be better addressed, as the applied model provides a management tool to estimate response of Tamarugo trees to changing soil moisture. To further improve the model and its use to assess Tamarugo survival, more field data, such as soil hydrodynamic properties and soil moisture, should be collected. Additionally, relationships between the state of the Tamarugo trees and soil moisture should be further constructed. In this way, the developed model will be able to predict future conditions associated to the Tamarugo&rsquo, s health state.

Bioretention is considered one of the best management practices (BMPS) for managing stormwater quality and quantity. The bioretention system has proven good performance in removing total suspended solids, oil, and heavy metals. The nitrogen (N) removal efficiency of the bioretention system is insufficient, however, due to the complex forms of nitrogen. Therefore, this paper aims to review recent enhancement approaches to nitrogen (N) removal and to discuss the factors influencing bioretention efficiency. To improve bioretention efficiency, several factors should be considered when designing bioretention systems, including nitrogen concentration, climate factors, and hydrological factors. Further, soil and plant selection should be appropriate for environmental conditions. Three design improvement approaches have been reviewed. The first is the inclusion of a saturated zone (SZ), which has been used widely. The SZ is shown to have the best performance in nitrogen removal. The second approach (which is less popular) is the usage of additives in the form of a mixture with soil media or as a separated layer. This concept is intended to be applied in tropical regions with wet soil conditions and a short dry period. The third approach combines the previous two approaches (enhanced filter media and applying a SZ). This approach is more efficient and has recently attracted more attention. This study suggests that further studies on the third approach should be carried out. Applying amendment material through filter media and integrating it with SZ provides appropriate conditions to complete the nitrogen cycle. This approach is considered a promising method to enhance nitrogen removal. In general, the bioretention system offers a promising tool for improving stormwater quality.

The introduction of a saturated zone (SZ) has been recommended to address the issue of nitrogen removal fluctuation in the bioretention system, which is one of the most versatile low-impact development facilities for urban stormwater management. Nine experimental columns were used to characterize the nitrogen concentration variations over the outflow during wetting periods and in SZ during the antecedent drying periods (ADPs), as well as compare removal efficiencies of various nitrogen species in systems with different SZ depths under alternate drying and wetting conditions. Results indicated that NO3−-N concentrations in the outflow showed quasi-logistic curve-shaped variations over time: being low (

International audience; Ground penetrating radar (GPR) is a non-destructive method which, over the past 10 years, has been successfully used not only to estimate the water content of soil, but also to detect and monitor the infiltration of pollutants on sites contaminated by light non-aqueous phase liquids (LNAPL). We represented a model water table aquifer (72 cm depth) by injecting water into a sandbox that also contains several buried objects. The GPR measurements were carried out with shielded antennae of 900 and 1200 MHz, respectively, for common mid point (CMP) and constant offset (CO) profiles. We extended the work reported by Loeffler and Bano by injecting 100 L of diesel fuel (LNAPL) from the top of the sandbox. We used the same acquisition procedure and the same profile configuration as before fuel injection. The GPR data acquired on the polluted sand did not show any clear reflections from the plume pollution; nevertheless, travel times are very strongly affected by the presence of the fuel and the main changes are on the velocity anomalies. We can notice that the reflection from the bottom of the sandbox, which is recorded at a constant time when no fuel is present, is deformed by the pollution. The area close to the fuel injection point is characterized by a higher velocity than the area situated further away. The area farther away from the injection point shows a low velocity anomaly which indicates an increase in travel time. It seems that pore water has been replaced by fuel as a result of a lateral flow. We also use finite-difference time-domain (FDTD) numerical GPR modelling in combination with dielectric property mixing models to estimate the volume and the physical characteristics of the contaminated sand.

International audience; Environmental management such as recommended by the European Water Framework Directive requires actions regarding diffuse pollution. However, the efficiency of these actions depends on the reaction time of the hydrosystem. In order to predict future groundwater-quality trends, especially after implementation of environmental measures such as substitution of pesticides or reduction of nitrogen loads, the response time has to be determined. In the case of diffuse pollution, the response time between fertilizer or pesticide application and the subsequent contamination of a spring or well may depend on the distance between the area where the products are spread and the point where water quality is measured. However, some aquifer systems may appear particularly slow, independently of the size of the catchment. At Montreuil-sur-Epte (Val d'Oise, France), no significant change in groundwater quality can be related to the suppression of atrazine application over the small agricultural catchment (4 sq km) of the Brévilles spring, 8 years ago (4 years before the national ban of atrazine). Besides the 8 year monitoring of groundwater quality at the spring and in several observation wells in its catchment, a particular attention was paid to the characterization of water and solute-infiltration rates at different scales. The role of each compartment (soil, and unsaturated and saturated zones) in the slowing down of flow and the transfer of solutes (pesticides and nitrate) from top soil to aquifer, and then to the spring, was determined by a multidisciplinary approach involving mainly soil science, hydrogeology and geochemistry. Detailed investigations aimed at identifying and quantifying the parameters that contribute to the inertia of the system, resulting in a long-term transfer of diffuse pollution. Data covering the monitoring of pesticide transfer in soil, the physico-chemical characteristics of soils, profiles of water contents, tritium activities, and nitrate concentrations measured on rock samples collected by drilling, were compared in order to describe the transfer time in soil and within several meters of unsaturated zone. Tracer tests in groundwater completed the understanding of transport in the saturated zone near the spring. Geochemical measurements and pumping tests confirmed the stratification of the saturated sandy aquifer leading to heterogeneous groundwater contamination. Finally, the inertia of the system results from several factors linked to the hydraulic properties of each underground compartment combined to intrinsic properties of the contaminants, partially explaining the limited improvement of groundwater quality 8 years after a major change in agricultural practice. The observations and results obtained by applying various tools and methods in this catchment led to a reflexion on sampling frequency, methodology and metrology to be adapted to this particular, but not unique, hydrogeological context in order to assess the groundwater-quality evolution and to understand the fate of solutes. The results of this study also raise questions on how efficient and how fast will the positive impact of product substitution or environmental regulations be.

Nitrate is necessary for agricultural productivity, but can cause considerable problems if released into aquatic systems. Agricultural land is the major source of nitrates in UK groundwater. Due to the long time-lag in the groundwater system, it could take decades for leached nitrate from the soil to discharge into freshwaters. However, this nitrate time-lag has rarely been considered in environmental water management. Against this background, this paper presents an approach to modelling groundwater nitrate at the national scale, to simulate the impacts of historical nitrate loading from agricultural land on the evolution of groundwater nitrate concentrations. An additional process-based component was constructed for the saturated zone of significant aquifers in England and Wales. This uses a simple flow model which requires modelled recharge values, together with published aquifer properties and thickness data. A spatially distributed and temporally variable nitrate input function was also introduced. The sensitivity of parameters was analysed using Monte Carlo simulations. The model was calibrated using national nitrate monitoring data. Time series of annual average nitrate concentrations along with annual spatially distributed nitrate concentration maps from 1925 to 2150 were generated for 28 selected aquifer zones. The results show that 16 aquifer zones have an increasing trend in nitrate concentration, while average nitrate concentrations in the remaining 12 are declining. The results are also indicative of the trend in the flux of groundwater nitrate entering rivers through baseflow. The model thus enables the magnitude and timescale of groundwater nitrate response to be factored into source apportionment tools and to be taken into account alongside current planning of land-management options for reducing nitrate losses.

International audience; The hydrochemical response at springs in the drainage area of the Sierra del Rey--Los Tajos carbonate aquifer (province of Ma'laga, southern Spain) was monitored in order to determine the hydrogeological functioning of this aquifer. Analysis of the most important chemical parameters, using methodologies such as the temporal evolution of chemical components, principal component analysis and discriminant factorial analysis revealed that the high level of hydrochemical heterogeneity to be found in this discharge zone, in addition to particular spatial and temporal factors, is responsible for the mineralisation of the spring water. Sampling in karst systems where discharge occurs by several springs should take into account the hydrochemical variability of them; otherwise conclusions about the hydrological functioning of aquifers deduced from mixture of spring waters can be inaccurate.

Transport modalities in karst aquifers are complex. Current methods do not allow quantification and identification of transport processes occurring over very short time scales. Resuspension and deposition of sediment occurring during flood conditions must be analysed at a high temporal resolution. These phenomena, occurring over very short time scales, can affect the water balance at the scale of the hydrologic year. This paper presents the application of univariate clustering for a hydrologic year at a karst spring. The results are consistent with those obtained by usual methods at the flood time scale. Moreover, this new method allows decomposition of the annual volume of spring water into its various transport modalities. For this example, the discharge of water from the spring over the course of a year was decomposed into four components: groundwater (47.7%), surface storm-derived water accompanied by the direct transfer of particles (23.7%), whereas 28.6% of the annual water balance is associated with periods of deposition (February to May, 13.2%) or resuspension (June to August, 15.4%).

The total dissolved inorganic carbon (TDIC) and 13CTDIC have been used as chemical and isotopic tracers to evaluate the contribution of different water components discharging at the Fontaine de Vaucluse karst spring near Avignon. At the same time they have been used to separate its flood hydrograph. Waters flowing from unsaturated zone (UZ) and saturated zone (SZ) show similar concentration in TDIC. In UZ and SZ water rock interactions do not obey to the same kinetic. The mixing rate between water coming from the UZ characterised by a short residence time and water from the SZ with a longer residence time has been evaluated in the spring discharge. In a hydrodynamic system, which is rather complex as it is open to the soil CO2 in UZ and closed to the same CO2 in the SZ, 13CTDIC has excellent characteristics as an environmental tracer. In order to better describe the inwardness of mass movements within the aquifer, the apparent contrasting information obtained using two different isotopes (18O of water molecules and 13C of TDIC) must be combined. 18O informs whether the hydrodynamic system acts as piston flow (PF) or follows a well mixing model (WMM). Conversely, 13C gives more complete information on the UZ contributes to the total discharge.