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• A screening tool named Colloids-Enhanced Transport (CET) model is developed. • The CET model is based on the enhanced transport of organic pollutants by soil colloids. • The CET model can predict the leaching potential of organic pollutants into groundwater. • The CET model can be used to derive soil quality standards or cleanup target levels. Modeling the fate and transport of organic pollutants at contaminated sites is critical for risk assessment and management practices, such as establishing realistic cleanup standards or remediation endpoints. Against the conventional wisdom that highly hydrophobic persistent organic pollutants (POPs) (e.g., polybrominated diphenyl ethers and polycyclic aromatic hydrocarbons) in surface soils are essentially immobile, mounting evidence has demonstrated the potential of these contaminants leaching into the groundwater, due to enhanced transport by soil colloids. Here, we develop a Colloids-Enhanced Transport (CET) model, which can be used as a simple screening tool to predict the leaching potential of POPs into groundwater, as mediated by soil colloids. The CET model incorporates several processes, including the release of POPs-bearing colloids into the porewater, the vertical transport of colloids and associated POPs in the vadose zone, the mixing of POPs-containing soil leachate with groundwater, and the migration of POPs-bearing colloids in saturated zone. Thus, using parameters that can be easily obtained (e.g., annual rainfall, soil type, and common hydrogeological properties of the subsurface porous media), the CET model can estimate the concentrations of POPs in the saturated zone from the observed POPs concentrations in surface or shallow subsurface zones. The CET model can also be used to derive soil quality standards or cleanup endpoints by back-calculating soil concentrations based on groundwater protection limits. [Display omitted] [ABSTRACT FROM AUTHOR]

Greywater is an alternative water resource, having many favourable characteristics over stormwater or wastewater. In particular, it can be supplied consistently and generated close to desirable end-use applications. Although greywater is considered to contain a low level of contamination, treatment is still required before the end-use, and passive filtration such as biofiltration became a popular option due to its low maintenance and low energy consumption. To this end, a laboratory experiment was conducted with synthetic greywater over 12 months to test the influence of operational characteristics and design factors on pathogen removal from greywater. The role of plants types, saturated zone, and the absence/inclusion of antimicrobial material were tested in a total of 80 biofilter columns. The results showed that the biofilters obtained a median E. coli logarithmic removal of 3.0 across the tested configurations and produced quality of water that meets indoor non-potable use standard (NRMMC, 2006). Further, the infiltration rate and event size were found to significantly influence E. coli removal in greywater biofilters (ANOVA, p < 0.05). The presence of antimicrobial media also significantly improved E. coli removal (up to 1.4 log) compared to non-amended media (ANOVA, p < 0.05). Vegetation also played a significant role in removing E. coli (ANOVA < 0.05). This study successfully suggested the great potential for the application of biofilters to greywater treatment and identified key design factors for consideration prior to implementation. [ABSTRACT FROM AUTHOR]

Plants play a critical role in the nutrient removal performance of stormwater biofilters. However, the influence of biofilter design on plant growth and subsequent implications for treatment performance are not well understood. A 12 month, laboratory-scale biofilter column experiment was conducted to investigate the response of Carex appressa to variations in biofilter design and implications for nutrient removal performance. Plant growth in Skye sand, a natural iron-coated sand with a strong capacity to immobilize phosphorus, was evaluated against a typical loamy sand filter media in biofilters with and without a saturated zone. Plant biomass correlated strongly with nutrient removal and was significantly greater in biofilters with a saturated zone, suggesting that inclusion of a saturated zone facilitates nutrient uptake. In the presence of a saturated zone, plants grown in Skye sand had a significantly higher specific root length, surface area and volume than plants grown in loamy sand, illustrating C. appressa ’ s ability to adapt root morphology to maintain growth under nutrient limited conditions. These root traits also correlated strongly with nutrient removal, suggesting that use of Skye sand in biofilters rather than loamy sand would be advantageous for nutrient removal. However, root adaptations, in particular increased etiolation, can make plants vulnerable to stressful environments (e.g. prolonged drying). Therefore, it is critical that a saturated zone be included in stormwater biofilters to increase growth and protect against drying. [ABSTRACT FROM AUTHOR]

Stormwater runoff greatly contributes to surface water pollution and deterioration of aquatic environment in urban areas. Biofilter, as low impact development (LID) technology, has been widely applied in controlling urban runoff pollution in recent years. A multi-layered biofilter with a saturated zone was employed in this study to test its removal efficiency of pollutants and the effect of saturation time on its performance with the real road runoff. Two groups of columns were built with different vegetations ( Zoysia matrella , ZM and a combination of Iris pseudacorus and Z. matrella , IZ). During a 2.5-month duration, five times of runoff dosing trials with collected stormwater were conducted at a load of 20–25 L day −1 . All filter systems had effective retention of particulate matters, with the turbidity removals of over 95%. The IZ group performed more efficiently than ZM systems in the removal of total phosphorus (TP), ammonia (NH 4 -N), nitrate (NO 3 -N) and turbidity. The mean removal of total nitrogen (TN) and TP was 49.8 ± 23.8% and 74.8 ± 9.9% in IZ group, and 42.6 ± 22.0% and 66.4 ± 12.2% in ZM group. Saturation time had significant effect on the removal of TN, TP and turbidity, whose concentrations declined with the saturation duration. The performances of biofilters were dynamic, as a function of media depth and retention time. The configuration of saturated zone and optimized depth of media layers (at least 0.75 m) can provide a favorable condition for nitrogen removal under random inflow condition. [ABSTRACT FROM AUTHOR]

Biochar has demonstrated promising performance as an amendment to biofilter soil media in removing fecal indicator bacteria (FIB) from simulated stormwater. However, there is no study that investigates its efficacy in treating natural stormwater runoff. Additional information, including the effects of antecedent dry period, microbial biofilm, and presence of a saturation zone on the performance of biochar-augmented biofilters are needed to inform their field implementation. This study uses laboratory column experiments to monitor FIB (enterococci and Escherichia coli ) and nutrient removal capacity of biochar-amended biofilters for 140 days using natural stormwater. Our study also investigates the effects of antecedent dry days (ADD) and the presence of a saturation zone (SZ) on the performance of lab-scale biochar-amended biofilters. The results suggest insignificant influence of the ADD and SZ on FIB removal performance, however biofilters with a SZ perform significantly better in removing nitrate-nitrogen compared to those without a SZ. In addition, it appears that the presence of biofilm augments nutrient removal capacity but reduces FIB removal capacity. Our observations indicate that biochar-amended biofilters are able to treat (to comply with recreational water quality standard for FIB) urban stormwater runoff for the duration of the experiment. Nitrate- and ammonium-nitrogen removal in the biologically aged biofilters is found to be 50–60% while the total dissolved phosphorus and the organic nitrogen removal is 20–30%. Our results inform full-scale design of biochar-amended biofilters in order to meet the total maximum daily load (TMDL) and municipal separate storm sewer system (MS4) permitting requirement for FIB and nutrients. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Nitrate water pollution, which is mainly caused by agricultural activities, remains an international problem. It can cause serious long-term environmental and human health issues due to nitrate time-lag in the groundwater system. However, the nitrate subsurface legacy issue has rarely been considered in environmental water management. We have developed a simple catchment-scale approach to investigate the impact of historical nitrate loading from agricultural land on the nitrate-concentration trends in sandstones, which represent major aquifers in the Eden Valley, UK. The model developed considers the spatio-temporal nitrate loading, low permeability superficial deposits, dual-porosity unsaturated zones, and nitrate dilution in aquifers. Monte Carlo simulations were undertaken to analyse parameter sensitivity and calibrate the model using observed datasets. Time series of annual average nitrate concentrations from 1925 to 2150 were generated for four aquifer zones in the study area. The results show that the nitrate concentrations in ‘St Bees Sandstones’, ‘silicified Penrith Sandstones’, and ‘non-silicified Penrith Sandstones’ keep rising or stay high before declining to stable levels, whilst that in ‘interbedded Brockram Penrith Sandstones’ will level off after a slight decrease. This study can help policymakers better understand local nitrate-legacy issues. It also provides a framework for informing the long-term impact and timescale of different scenarios introduced to deliver water-quality compliance. This model requires relatively modest parameterisation and is readily transferable to other areas. [ABSTRACT FROM AUTHOR]

BIOCHLOR is a well-known simple tool for evaluating the transport of dissolved chlorinated solvents in groundwater, ideal for rapid screening and teaching. This work extends the BIOCHLOR model for the calculation of stable isotope ratios of carbon and chlorine isotopes in chloroethenes. An exact solution for the three-dimensional reactive transport of a chain of degrading compounds including sorption is provided in a spreadsheet and applied for modeling the transport of individual isotopes 12 C, 13 C, 35 Cl, 37 Cl from a constant source. The model can consider secondary isotope effects that can occur in the breaking of C Cl bonds. The model is correctly reproducing results for δ 13 C and δ 37 Cl modeled by a previously published 1-D numerical model without secondary isotope effects, and is also reproducing results from a microcosm experiment with secondary chlorine isotope effects. Two applications of the model using field data from literature are further given and discussed. The new BIOCHLOR-ISO model is distributed as a spreadsheet (MS EXCEL) along with this publication. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary Riparian zones are considered potential hotspots of denitrification because they allow for the confluence of necessary electron acceptors (nitrate) and donors (carbon) via hydrologic flowpaths in low oxygen (reducing) conditions. While riparian areas have received considerable research attention, other soils prone to saturation have similar physicochemical characteristics but are less frequently studied. We quantified in situ denitrification rates in the shallow saturated zone, a dynamic portion of the landscape, across a range of hydroperiodicities, i.e., frequencies and durations of saturated conditions, as characterized by a topographic index in a small mixed land-use headwater catchment in central New York State. We found a strong positive relationship between topographic index and denitrification, indicating that the highest rates of denitrification occur in the relatively small portion of the landscape prone to saturation. We used the resulting relationship to distribute denitrification rates across the catchment and estimate denitrification fluxes from the shallow saturated zone. While the highest rates of denitrification were observed in wetter portions of the landscape, including riparian zones, we found that the shallow saturated zone beneath drier upland soils contributed to a larger portion of whole-catchment denitrification due to a larger areal extent. A topographic index-denitrification model is a promising and simple tool that allows for scaling of in situ denitrification rates across the landscape and provides insight into the spatial organization of denitrification at the catchment scale. [ABSTRACT FROM AUTHOR]

Highlights: [•] Denitrification rates were highly correlated to soil saturation frequency as described by the soil topographic index. [•] Denitrification from seasonally saturated soils accounted for about half of the total nitrogen imbalance in this headwater catchment. [•] Denitrification rates from riparian areas were high but only accounted for about 10% of the total nitrogen imbalance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rainfall-runoff experiments and simulations were conducted on a hillslope system. [•] A saturated area formed at the slope toe, rose to the surface and expanded upslope. [•] Rainfall intensity affected surface runoff but not the maximum subsurface discharge. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen excess is a key trigger for eutrophication of water bodies. Stormwater can be an important N source in urban environments and thus requires effective treatment. Stormwater biofilters can remove a wide range of pollutants. However, removal of N is often insufficient due to a lack of denitrification in freely drained biofilters. We tested whether existing stormwater biofilters with poor N removal could be enhanced if a saturated zone is retrofitted to create anaerobic conditions for effective denitrification. We evaluated this by measuring removal of nitrogen, phosphorus and metals in retrofitted biofilters using laboratory mesocosms. For over 18 months five replicates of typical biofiltration configurations, that include freely draining 690mm deep loamy sand media above a 140mm deep transition layer and a 70mm gravel layer planted with popular plant species (Dianella revoluta, Microlaena stipoides and Carex appressa), were tested for typical operational conditions. The biofilter columns planted with D. revoluta and M. stipoides showed poor N removal, while biofilters planted with C. appressa were performing well. All columns were then retrofitted with a 450mm deep saturated zone, and testing continued using the same operational conditions. After retrofitting the saturated zone, NO x removal was significantly increased (mean increase: 370% for Dianella and 180% for Microlaena) which enhanced overall N removal. TP removal was less efficient after retrofitting the saturated zone due to presence of organic matter in the filter media within the saturated zone. The removal of metals was not affected in practical terms, despite some statistically significant effects. The results of this study suggest that retrofitting a saturated zone in existing standard biofilters should be recommended if the existing filter has inadequate N removal and if N discharges pose a potential threat to the receiving environment. [Copyright &y& Elsevier]

Abstract: Biofiltration is a technology applied to treat urban stormwater runoff that transports various pollutants, including pathogens. However, the pathogen removal performance of biofiltration systems remains unknown. A laboratory study was conducted to investigate the removal of three indicator organisms (Clostridium perfringens, Escherichia coli, and F-RNA coliphages) by biofilters. The influence of a range of factors was investigated: presence of vegetation, depth and types of filter media, presence of a saturated zone at the base of the biofilter, and intermittent wetting and drying conditions. The mean removal of C. perfringens and F-RNA coliphages by all biofilter designs exceeded 3log. E. coli removal during wet periods, however, was much lower (mean 2log). Furthermore, antecedent drying decreased the E. coli removal efficiency significantly (p <0.05). Drying might induce fine fissures or macropore formation in filter media thus reduced retention of microbes. This effect may be more obvious in vegetated designs due to evapotranspiration induced moisture loss. Introducing a saturated zone and carbon source at the base of the filter eliminated such negative effects of drying on E. coli removal. The effluent from biofilters with a saturated zone and carbon source met the recommended water quality for secondary contact recreational water use in relation to E. coli. [Copyright &y& Elsevier]

Abstract: Three-dimensional models of hydraulic conductivity and porosity are essential to understand and simulate groundwater flow in heterogeneous geological environments. However, considering the inherent limitations of traditional hydrogeological field methods in terms of resolution, alternative field approaches are needed to establish such 3-D models with sufficient accuracy. In this study, we developed a workflow combining 3-D structural information extracted from ground penetrating radar (GPR) images with 1-D in situ physical-property estimates from direct-push (DP) logging to construct a 3-D hydrostratigraphic model. To illustrate this workflow, we collected an ∼70m×90m 100MHz 3-D GPR data set over a shallow sedimentary aquifer system resolving six different GPR facies down to ∼15m depth. DP logs of the relative dielectric permittivity, the relative hydraulic conductivity, the cone resistance, the sleeve friction and the pore pressure provided crucial data (1) to establish a GPR velocity model for 3-D depth migration and to check the time-to-depth conversion of the GPR data, and (2) to construct a 3-D hydrostratigraphic model. This model was built by assigning porosity values, which were computed from the DP relative dielectric permittivity logs, and DP relative hydraulic conductivity estimates to the identified GPR facies. We conclude that the integration of 3-D GPR structural images and 1-D DP logs of target physical parameters provides an efficient way for detailed 3-D subsurface characterization as needed, for example, for groundwater flow simulations. [Copyright &y& Elsevier]

Summary: From analysis of the hydrodynamic and hydrochemical responses of karst springs, it is possible to know the behaviour of the aquifers they drain. This manuscript aims to contribute to the characterization of infiltration process, and to determine the relative importance of the saturated zone and of the unsaturated zone in the hydrogeological functioning of carbonate aquifers, using natural hydrochemical tracers. Thus, chemical components together with temperature and electrical conductivity (both punctual and continuous records) have been monitored in three springs which drain Alta Cadena carbonate aquifer, Southern Spain. An evaluation of the percentage of the electrical conductivity frequency peaks determined for each of the three springs is linked to the chemical parameters that comprise the conductivity signal. One of these springs responds rapidly to precipitation (conduit flow system), due to the existence of a high degree of karstification in the unsaturated zone and in the saturated zone, both of which play a similar role in the functioning of the spring. Another spring responds to precipitation with small increases in water flow, somewhat lagged, because the aquifer has a low degree of karstification, even in the unsaturated zone, which seems to influence its functioning more strongly than does the saturated zone. The third spring drains a sector of the aquifer with a moderately developed degree of karstification, one that is intermediate between the other two, in which both the unsaturated zone and the saturated zone participate in the functioning of the spring, but with the latter zone having a stronger influence. These three springs show different hydrogeological functioning although they are in similar geological and climatic contexts, which show the heterogeneity of karst media and the importance of an adequate investigation for groundwater management and protection in karst areas. [ABSTRACT FROM AUTHOR]

Abstract: This work presents analytical models which are able to predict contours of concentrations and isotope ratios of organic pollutants in homogeneous aquifers. Four analytical solutions of the advective–dispersive transport equation for reactive transport from the literature differing in assumptions regarding biodegradation kinetics were used. Stable isotope ratios are computed after modelling the individual reactive transport of isotopic species in the aquifer, which respond differently to fractionation by biodegradation or sorption. The main finding of this study is that the isotope ratios in the plumes are very sensitive to the assumptions underlying the biodegradation kinetics in the models. When biodegradation occurs throughout the core of the plume as first-order reaction, the transversal gradients in isotope ratios are smooth. When biodegradation occurs in a bi-molecular reaction with an electron acceptor (modelled by double-Monod kinetics), steep transversal isotope gradients are predicted. When the reaction rates approach instantaneous reaction along the plume fringes, isotope shifts in the core of the plume disappear. A model incorporating plume and fringe degradation produces the most plausible predictions of isotope ratios in this study. It is shown furthermore that isotope fractionation by sorption causes an even different pattern of isotope ratios, with positive shifts restricted to near the forerunning front of an expanding plume. The models developed in this work can serve for the validation of numerical models and may be incorporated in natural attenuation support systems such as e.g. BIOSCREEN. [Copyright &y& Elsevier]

Summary: 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 (4sqkm) 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. [Copyright &y& Elsevier]

Abstract: Many long-lived radionuclides are present in groundwater at the Nevada Test Site (NTS) as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. In conjunction with a comprehensive geochemical review of radionuclides (3H, 14C, 36Cl, 99Tc and 129I) that are presumably mobile in the subsurface, we synthesized a body of radionuclide activity data measured from groundwater samples collected at 18 monitoring wells, to qualitatively assess their migration at the NTS over distances of hundreds of meters and over timescales of decades. Tritium and 36Cl showed little evidence of retardation, while the transport of 14C may have been retarded by its isotopic exchange with carbonate minerals in the aquifer. Observed local reducing conditions (either natural or test-induced) will impact the mobility of certain redox-sensitive radionuclides (especially 99Tc) that were otherwise soluble and readily transported under oxidizing conditions. Conversely, strongly oxidizing conditions may impact the mobility of 129I which is mobile under reducing conditions. The effect of iodine speciation on its transport deserves further attention. Indication of delayed transport of some “mobile” radionuclides (especially 99Tc) in the groundwater at the NTS suggested the importance of redox conditions of the natural system in controlling the fate and transport of radionuclides, which has implications in the enhanced performance of the potential Yucca Mountain repository, located adjacent to the NTS, to store high-level nuclear wastes as well as management of radionuclide contamination in legacy nuclear operations facilities. [Copyright &y& Elsevier]

Abstract: The first three, successive Editors-in-Chief of Agricultural Water Management, Jans Wesseling, Jan van Schilfgaarde, and Herman Bouwer, were of Dutch origin, received their early training immediately after World War II, and started their careers in the early 1950s: Jans in The Netherlands and Jan and Herman in the USA. In this paper we review the circumstances and the highlights of their contributions to responsible management of water in agriculture. Following a sketch of the state of agricultural water management research around 1950, both in The Netherlands and in the USA, we describe their training, document their early scientific contributions, especially in the realm of agricultural drainage, and highlight their later service as research managers. The three careers reflect the great progress in the second half of the 20th century: the scope of water management research widened, computational capabilities became more powerful, experimental methods became more sophisticated. With increasing attention for environmental implications of water management, the focus of research changed from mainly water quantity to both water quantity and quality. The review of the careers of the first three Editors-in-Chief shows that the journal Agricultural Water Management from its inception and throughout its first quarter century was in very good hands. [Copyright &y& Elsevier]

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed. [Copyright &y& Elsevier]

Evaluation of radionuclide transport in the saturated zone (SZ) to the accessible environment is an important component of performance assessment for the proposed radioactive waste repository at Yucca Mountain. Simulations of radionuclide migration in the SZ have been performed using the calibrated three-dimensional (3-D) SZ site-scale flow and transport model. An innovative particle-tracking method was used to simulate transport that includes the processes of advection, dispersion, matrix diffusion, and sorption. The uncertainties in groundwater flow and radionuclide transport were quantitatively evaluated to develop uncertainty distributions for key model parameters, and multiple realizations of the SZ system were simulated using the SZ site-scale model. The results of multiple realizations of radionuclide transport indicate significant aggregate uncertainty in transport times through the SZ. The simulated radionuclide mass breakthrough curves in the SZ have been coupled with other components of the repository system in Total System Performance Assessment (TSPA) analyses and constitute the means by which uncertainty in the SZ is incorporated into regulatory analyses. Regression analysis has been used to determine the sensitivity of radionuclide transport simulation results to the uncertainty of individual model input parameters. Results of the sensitivity analysis indicate that median radionuclide transport times were dominantly controlled by uncertainty in the specific discharge in the SZ, with sorption and retardation in the alluvium playing important roles for some radionuclides. [Copyright &y& Elsevier]

The US Department of Energy is pursuing Yucca Mountain, Nevada, for the development of a geologic repository for the disposal of spent nuclear fuel and high-level radioactive waste, if the repository is able to meet applicable radiation protection standards established by the US Nuclear Regulatory Commission and the US Environmental Protection Agency (EPA). Effective performance of such a repository would rely on a number of natural and engineered barriers to isolate radioactive waste from the accessible environment. Groundwater beneath Yucca Mountain is the primary medium through which most radionuclides might move away from the potential repository. The saturated zone (SZ) system is expected to act as a natural barrier to this possible movement of radionuclides both by delaying their transport and by reducing their concentration before they reach the accessible environment. Information obtained from Yucca Mountain Site Characterization Project activities is used to estimate groundwater flow rates through the site-scale SZ flow and transport model area and to constrain general conceptual models of groundwater flow in the site-scale area. The site-scale conceptual model is a synthesis of what is known about flow and transport processes at the scale required for total system performance assessment of the site. This knowledge builds on and is consistent with knowledge that has accumulated at the regional scale but is more detailed because more data are available at the site-scale level. The mathematical basis of the site-scale model and the associated numerical approaches are designed to assist in quantifying the uncertainty in the permeability of rocks in the geologic framework model and to represent accurately the flow and transport processes included in the site-scale conceptual model. Confidence in the results of the mathematical model was obtained by comparing calculated to observed hydraulic heads, estimated to measured permeabilities, and lateral flow rates calculated by the site-scale model to those calculated by the regional-scale flow model. In addition, it was confirmed that the flow paths leaving the region of the potential repository are consistent with those inferred from gradients of measured head and those independently inferred from water-chemistry data. The general approach of the site-scale SZ flow and transport model analysis is to calculate unit breakthrough curves for radionuclides at the interface between the SZ and the biosphere using the three-dimensional site-scale SZ flow and transport model. Uncertainties are explicitly incorporated into the site-scale SZ flow and transport abstractions through key parameters and conceptual models. [Copyright &y& Elsevier]

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. • Foam can efficiently divert lateral water flow in highly permeable porous media. • High gas saturation after foam destruction leads to reduce the mobility. • Lateral flow velocity significantly affects foam stability. • Recirculation of water containing the surfactant increases foam stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sufficient removal of pollutants was achieved despite the salinity varied. • Removal of COD, NH 4 +-N, TIN and TP occurred mainly within the unsaturated zone. • Microbial community exhibited succession with salinity elevated. • Unsaturated zone benefited the enrichment of functional group for nutrient removal. This study investigated the influence of salinity on pollutant removal and bacterial community within a partially saturated vertical flow constructed wetland (PS-VFCW). High removal rates of NH 4 +-N (88.29 ± 4.97–100 ± 0%), total inorganic nitrogen (TIN) (50.00 ± 7.21–62.81 ± 7.21%) and COD (91.08 ± 2.66–100 ± 0%) were achieved at 0.4–2.4% salinity levels. The removal of ammonia, TIN and organic matter occurred mainly in unsaturated zone. Salt-adaptable microbes became the dominant bacteria with salinity elevated. The proportion of ammonia-oxidizing bacteria (AOB) in the 0–5 cm depth layer (unsaturated zone) decreased obviously as the salinity increased to 2.4%. Nitrite-oxidizing bacteria (NOB) in the 0–5 cm depth layer showed a decreasing trend with elevated salinity. Denitrifying bacteria (DNB) in the 0–5 cm depth layer maintained high abundance (27.70–53.60%) at 0.4–2.4% salinity levels. At 2.4% salinity, AOB, NOB and DNB were observed in the unsaturated zones and saturated zones, and showed higher abundance in the unsaturated zone. [ABSTRACT FROM AUTHOR]

• Carbon dioxide CO 2 migration in carbonated aquifers within the context of Carbon Capture and Storage (CCS): pre-modelling of a CO 2 injection experiment in Saint Emilion, France. • Fluid flow model to simulate the migration of the following injected dissolved species: CO 2 , krypton, fluorescent molecule. • Sensitivity analysis of the uncertain model parameters in order to assess the working assumptions: assessment of the species concentration uncertainty. The objective of the Aquifer-CO 2 Leak project is to get insights into carbon dioxide CO 2 migration in aquifers within the context of Carbon Capture and Storage (CCS) and to test the different equipment necessary for CO 2 monitoring. The underlying idea is to develop an experiment in the saturated zone (phreatic) of the underground limestone quarry located at Gironde department (France). It consists in injecting water, carrying dissolved gases (CO 2 and krypton) and a fluorescent molecule, under controlled conditions. In this paper, we present the dimensioning study of the experiment by numerical simulations carried out using the simulator CooresFlow (IFPEN's in-house simulator for reactive transport in porous media). The important experiment parameters (injection flow rate, injected volume, the time to return in system equilibrium and wells location) were successfully estimated. In particular, the variation of species concentration in time and space was simulated and analyzed to define an experimental measurement schedule for the planned survey. Finally, a sensitivity analysis of the uncertain model parameters is presented. We found that the water table level and the dispersivity of the porous medium appear to be the most "sensitive" parameters. [ABSTRACT FROM AUTHOR]

• Sufficient removal of pollutants was achieved despite the temperature varied. • Removal of COD, NH 4 +-N, TIN and TP mainly occurred within the unsaturated zone. • Microbial community exhibited great succession with season as well as depth. • Unsaturated zone benefited the enrichment of functional group for nutrient removal. • Diverse mechanism of nitrogen removal existed in VFCW while varied along the depth. In this study, a partially-saturated vertical-flow constructed wetland (VFCW) with continuous-feed was operated to investigate nutrients transformation and possible pathways in unsaturated and saturated zones. Effect of temperature on nutrients removal and microbial community was also evaluated. The variation of temperature barely affected removal of NH 4 +-N and COD, achieving removal efficiencies of 99.5–100.0% and 96.8–100.0% at effluent temperature of 14.9–27.7 °C. The removal of COD, NH 4 +-N, total inorganic nitrogen (TIN) and total phosphorus mainly occurred in unsaturated zone, achieving much higher removal rates than saturated zone. Nitrification process in the VFCW was associated with autotrophic/heterotrophic ammonia oxidizing bacteria and nitrite oxidizing bacteria. Denitrification process relied on both autotrophic and heterotrophic denitrifiers. Anaerobic ammonium oxidizing bacteria was also detected, contributing to TIN removal. All of the groups for nutrients removal exhibited higher abundance in unsaturated zone. Diverse pathways co-existed for nitrogen removal, while the main metabolic pathways were different along the depth. [ABSTRACT FROM AUTHOR]