This chapter highlights the complexity of water and chemical phenomena that control the behaviour of contaminants in the unsaturated zone (UZ). Numerous mechanisms are involved in fixing these elements in soils, and many are not fully understood. This area of study is characterised by their hierarchy, or the predominance of one mechanism over another, depending on the bio-physico-chemical conditions of the environment. Understanding this hierarchy requires site analysis and measurements which currently are not always carried out. Nevertheless, estimating the potential risk of a moderately contaminated site in the medium and long term, determining its future use, predicting groundwater quality and optimally managing contaminated excavated material (waste and polluted soil) all require a good understanding of pollutant behaviour in time and space.

Complexation with methyl groups produces the most toxic form of mercury, especially because of its capacity to bioconcentrate in living tissues. Understanding and integrating methylation and demethylation processes is of the utmost interest in providing geochemical models relevant for environmental assessment. In a first step, we investigated methylation at equilibrium, by selecting the thermodynamic properties of different complexes that form in the chemical system Hg-SO3-S-Cl-C-H2O. The selection included temperature dependencies of the equilibrium constants when available. We also considered adsorption and desorption reactions of both methylated and non-methylated mercury onto mineral surfaces. Then we assessed the kinetics of methylation by comparing a dedicated column experiment with the results of a geochemical model, including testing different methylation and demethylation kinetic rate laws. The column system was a simple medium: silicic sand and iron hydroxides spiked with a mercury nitrate solution. The modelling of methylmercury production with two different rate laws from the literature is bracketing the experimental results. Dissolved mercury, iron and sulfate concentrations were also correctly reproduced. The internal evolution of the column was also correctly modeled, including the precipitation of mackinawite (FeS) and the evolution of dissolved iron. The results validate the conceptual model and underline the capacity of geochemical models to reproduce some processes driven by bacterial activity.

We introduce the INSPIRATION bottom-up approach for the development of a strategic research agenda for spatial planning, land use and soil-sediment-water-system management in Europe. Research and innovation needs were identified by more than 500 European funders, endusers, scientists, policy makers, public administrators and consultants. We report both on the concept and on the implementation of the bottom-up approach, provide a critique of the process and draw key lessons for the development of research agendas in the future. Based on identified strengths and weaknesses we identified as key opportunities and threats 1) a high ranking and attentiveness for the research topics on the political agenda, in press and media or in public awareness, 2) availability of funding for research, 3) the resources available for creating the agenda itself, 4) the role of the sponsor of the agenda development, and 5) the continuity of stakeholder engagement as bases for identification of windows of opportunity, creating ownership for the agenda and facilitating its implementation. Our derived key recommendations are 1) a clear definition of the area for which the agenda is to be developed and for the targeted user, 2) a conceptual model to structure the agenda, 3) making clear the expected roles, tasks, input formats regarding the involvement and communication with the stakeholders and project partners, 4) a sufficient number of iterations and checks of the agenda with stakeholders to insure completeness, relevance and creation of co-ownership for the agenda, and 5) from the beginning prepare the infrastructure for the network to implement the agenda.

Due to difficulty of access and the roles of subsurface lithology and geochemistry in determining water behavior and quality, groundwater sampling involves a number of specialized methodologies in addition to those applicable to surface water sampling. This chapter focuses on the quality assurance/quality control-related aspects of groundwater-specific sampling methodologies. Appropriate protocols for well purging and options for sampling different layers of an aquifer are important factors in reducing uncertainties in groundwater sampling data. Similarly, since the use of pumps, piping and tubing is an intrinsic part of groundwater sampling, these introduce potential sources of contaminants, as well as potential for loss or modification of analytes of interest. Recommendations are provided on groundwater sampling issues including minimum well numbers and locations, sampling frequency and duration, and field measurements that can be made in association with the collection of groundwater samples to improve the quality and interpretation of groundwater data.

L’article presente une etude menee sur le devenir du polyacrylamide et de l’acrylamide. Les resultats obtenus ont permis d’etablir un etat des lieux de la consommation des flocculants a base de polyacrylamide dans les carrieres, de developper des methods d’analyses de l’acrylamide dans les eaux et dans les boues ainsi que celles du polyacrylamide, de developper une methodologie d’echantillonnage sur site pour le suivi de ces deux molecules, d’identifier les micro-organismes impliques dans leur degradation, et de determiner les cinetiques de degradation de l’acrylamide et ses interactions avec les fines particules. Les acquis du projet serviront a emettre des recommandations pour diminuer l’impact des floculants sur l’environnement.

Aggregate quarries play a major role in land settlement. However, like all industrial operations, they can have impacts on the environment, notably due to the use of polyacrylamide (PAM)-based flocculants, which contain residual acrylamide (AMD), a carcinogenic, mutagenic, and reprotoxic monomer. In this study, the dissemination of AMD throughout the environment has been investigated in a French quarry. The presence of AMD has been determined in the process water and in the sludge, as well as in the surrounding surface water and groundwater. From the results of several sampling campaigns carried out on this case study, we can (a) confirm that the AMD contained in the commercial product is found in the quarry's water circuit (0.41 to 5.66 μg/l); (b) show that AMD is transported to the surrounding environment, as confirmed by the contamination of a pond near the installation (0.07 to 0.08 μg/l) and the presence of AMD in groundwater (0.01 to 0.02 μg/l); and (c) show that the sludge in both the current and former settling basins contains AMD (between 4 and 26 μg/kg of dry sludge). Therefore, we demonstrated in this case study that using PAM-based flocculants leads to the release of AMD to the environment beyond the treatment plant and creates a reserve of AMD in sludge basins.

Artificially synthetized chloride-based-oxyanions such as perchlorate (ClO4-) and chlorate (ClO3-), are used in a vast number of applications such as military and aerospace industry; they are also used as herbicides and in pyrotechnic applications. Due to their very high solubility, perchlorate and chlorate are readily transported in water systems and can thus end up in drinking water. Ingestion of perchlorate may affect iodine uptake by the human thyroid and thus thyroidal hormone production. Pollution by these oxyanions is an emerging problem in France and recent events of ground water contamination have increased concerns on the fate of these substances, thus encouraging research on its fate in the environment and effect on human health. As the transport of (liquid and gaseous) chloride is highly dangerous, it is generally transformed directly on site and thus other chloride molecules such as 1, 2 dichloroethane (DCA) which is a precursor of vinyl chloride (VC), can be found in the same locations. The work we present here involves a site that once produced perchlorate, chlorate, DCA and VC. Due to historical losses, all of these substances are present in the groundwater. Following groundwater characterisation, the aim of the present study was to identify a naturel attenuation potential on site by researching specific genes involved in chlorate and perchlorate reduction and DCA or VC dehalogenation and then linking gene presence to activity using laboratory batch cultures. After collecting biomass from 36 ground-water-samples, DNA was extracted and PCRs (polymerase chain reactions) were carried out to amplify genes coding for several enzymes; the pcaA gene coding for a alkane dehydrogenase, the dhLA gene coding for a haloalkanedehalogenase, the pcrA gene coding for a perchlorate reductase and the cld gene coding for a chlorite reductase. Moreover, global bacterial diversity was studied by amplifying the gene coding for RNA 16S and analysing diversity with an electrophoresis approach (DGGE, Denaturing Gel Gradient Electrophoresis). Bands of interest were purified and sequenced. The gene-screening-results closely recovered zones where the chemicals had been detected in concentrations over 10µg/l and were especially precise for DCA and CV whereas for perchlorate and chlorate it suggested that the pollution span was once larger that presently. Degradation potentials, in batchs incubated at 15°C, demonstrated first chlorate reduction then perchlorate reduction after a week's incubation in presence of an available carbon source (acetate and lactate) but no degradation in autotrophic conditions. DCA amounts also decreased in batchs but over a longer time span. Due to the pollution layout, where the perchlorate and chlorate plume encounters the DCA and VC one, experiments are presently being carried out to assess whether these organochlorides and/or their dechlorination metabolites can be used as a carbon source to fuel perchlorate and chlorate reduction, thus actively contributing to a naturel attenuation of this pollution. This potential could then be stimulated and used for in situ bioremediation. Indeed, total degradation of these molecules produces Cl-, CO2 and H2O and which are harmless for the environment.

CO2 capture and geological storage (CCS) is seen as a promising technology to achieve large reduction in atmospheric greenhouse gas emissions. But a prerequisite to its industrial scale implementation is demonstrating safety of deep reservoir storage. In this context, the need to know “what can be done” in case of abnormal behaviour of the reservoir has been outlined by the recent European directive on geological storage operations (directive 2009/31/EC, issued in April 2009). In the present article, we consider the remediation environmental problem of restoring the vadose zone from the potential impact associated with the CO2 leakage. In this view, we use an analogy-based approach. Considering the hydrodynamic impact, linked with the formation of a CO2 leakage plume and with the potential emission of the CO2 in the atmosphere, CO2 presents several similarities with Volatil Organic Compounds (VOC) for which remediation strategies have been developed for the last 20 years. These strategies can be divided into two main categories: (1) based on natural attenuation (i.e. concentration and global mass reduction) combined with active monitoring techniques; (2) based on active extraction techniques such as “Soil Vapour Extraction”. Generic modelling using the multiphase and multi-component TOUGH2/EOS7CA (Oldenburg et al., Transport in Porous Media, 2009) show good effectiveness of such strategies in case the CO2 leakage source is either of limited spatial extent or of moderate flux rate. Nevertheless, more complex strategies should be undertaken in case of large scale pollution (so-called « diffuse pollution »). Guidelines are proposed based on the lessons learned from diffuse pollution case studies with a special focus on Radon diffusion and pesticide contamination. Considering the geochemical impact, linked with the acidification owing to the CO2 dissolution and with the potential release of heavy metals, we define an intervention strategy based on the study of complex environmental remediation real cases in the fields of acidic mine drainage and industry contamination.

Two complementary approaches were used to characterize arsenic and metal mobilizations from a dredged-sediment disposal site: a detailed field study combined with hydrogeochemical modeling. Contaminants in sediments were found to be mainly present as sulfides subject to oxidation. Secondary phases (carbonates, sulfates, (hydr)oxides) were also observed. Oxidative processes occurred at different rates depending on physicochemical conditions and contaminant contents in the sediment. Two distinct areas were identified on the site, each corresponding to a specific contaminant mobility behavior. In a reducing area, Fe and As were highly soluble and illustrated anoxic behavior. In well-oxygenated material, groundwater was highly contaminated in Zn, Cd and Pb. A third zone in which sediments and groundwater were less contaminated was also characterized. This study enabled us to prioritize remediation work, which should aim to limit infiltration and long-term environmental impact.

La mise en depot de sediments de curage est une pratique courante dans certains bassins versants francais. Jusqu'a la fin des annees 80, celle-ci se faisait sans precaution particuliere et des materiaux parfois contamines en divers polluants organiques et inorganiques ont ete deposes sur des sols permeables. L'un de ces sites est a l'heure actuelle particulierement preoccupant en raison d'un niveau de contamination exceptionnel en divers elements inorganiques (de l'ordre du % en masse en Pb et Zn). L'alteration meteorique de ce sediment de curage depuis sa mise en depot en 1976 conduit a la formation d'un anthroposol au fonctionnement pedologique mal connu. Une premiere phase de caracterisation a l'echelle du profil (Bataillard et al., 2008) avait mis en evidence l'oxydation des sulfures comme le mecanisme preponderant a l'origine de la transformation geochimique du materiau. Cette alteration induit une forte mobilite du fer qui a egalement une incidence forte sur le devenir de la plupart des elements potentiellement toxiques (EPT) au cours de la pedogenese precoce. Cet article presente les resultats de caracterisation d'echantillons choisis le long du profil par des techniques spectroscopiques non destructives, permettant notamment de discuter des phases neoformees capables de fixer les EPT. La complementarite des techniques utilisees (microscopie electronique equipee d'une sonde d'analyse a energie dispersive, micro fluorescence X sur rayonnement synchrotron, emission de photons X induite par des particules chargees et analyse par reactions nucleaires), en mettant en evidence des associations majoritaires a l'echelle du micron, a confirme que les neoformations d'hydroxydes de fer sont des pieges pour les elements Zn, Pb, Se et As. Ces associations apparaissent localement dans le solum a la faveur d'une augmentation du potentiel redox. Dans le cas de Pb, cette association apparait quantitativement secondaire par rapport aux nombreux grains de carbonate de Pb observes dans les echantillons. De plus, dans la partie tres superficielle de l'horizon, probablement la plus alteree, apparait une association Pb, Se, As et P qui pourrait correspondre a un melange de phosphates, arseniate et selenate de Pb. Les observations ont egalement mis en evidence qu'une partie du stock de Zn et Pb se trouve dans des particules vitreuses, peu alterees, heritees du procede industriel de l'usine responsable de la contamination. Les resultats obtenus montrent l'absence de phase susceptible de pieger efficacement Cd au cours de la transformation geochimique du materiel mis en depot. Ce resultat est coherent avec un depart de l'ordre de 60% de cet element initialement present dans le sediment avant son alteration. La solubilite de certaines phases secondaires identifiees, comme le carbonate de plomb, et la stabilite des associations de surface, dependent des conditions physico-chimiques du milieu (force ionique, pH, Eh...). Ces neoformations constituent donc des pieges peu efficaces des elements traces et doivent etre considerees comme des sources potentielles de contaminants. Une synthese sur l'apport des techniques spectroscopiques pour l'etude de la speciation des ETM dans les sols est finalement proposee a l'issue de ce travail.

De nombreux acteurs se trouvent actuellement confrontes au probleme de la gestion de sites contamines et a leur rehabilitation. La mise en place de methodes de traitement dites classiques peut engendrer des investissements importants et se reveler difficile d'un point de vue technique, voire inefficace, notamment dans le cas de pollutions d'aquiferes ou de contamination etendue des sols. A partir de ce constat, la gestion des sites pollues peut etre abordee differemment en integrant une approche alternative privilegiant les mecanismes naturels de degradation et communement appelee attenuation naturelle surveillee (ANS).

Le maintien d'une profondeur d'eau suffisante des voies de navigation necessite leur curage regulier. Le devenir le plus frequent des materiaux dragues est la mise en depot a proximite du lieu d'extraction. Jusqu'a il y a une vingtaine d'annee celle-ci se faisait sans precaution particuliere et dans certaines regions industrialisees, des materiaux contamines en divers polluants organiques et inorganiques ont ete deposes sur des sols drainants. L'un de ces sites est a l'heure actuelle particulierement preoccupant en raison d'un niveau de contamination exceptionnel en divers elements inorganiques (Pb, Zn, Cd, As, Se...). L'alteration meteorique de ce sediment de curage depuis sa mise en depot en 1976 conduit a la formation d'un anthroposol au fonctionnement pedologique mal connu. Les potentialites de transfert des polluants vers la nappe de la craie ne sont donc pas apprehendees a l'heure actuelle. Au cours de ce travail, des observations de terrain, suivies de caracterisations au laboratoire, ont ete entreprises pour comprendre les processus pedogenetiques impliques dans la transformation du sediment et en deduire leur impact sur la mobilisation des polluants au cours du temps. Les observations de terrain jusqu'a un metre de profondeur environ ont montre que le materiau tres contamine constitue l'horizon de surface d'un profil pedologique complexe dont la structure generale est en grande partie due a la succession de phases de depot differees dans le temps. L'horizon de surface presente des fractures quasi verticales de largeur parfois centimetrique qui sont des passages preferentiels des eaux meteoriques. Il en decoule un gradient d'alteration a l'echelle du decimetre entre le materiau au contact de la fracture et celui plus eloigne des passages preferentiels des fluides oxydants. Une analyse fine des teneurs totales en elements de deux materiaux correspondant a des degres d'alteration differents, couplee a un traitement statistique des donnees obtenues, a permis de mettre en evidence un depart de pres de 60% du Cd et 20% du Zn du materiel initial apres environ 25 ans d'alteration. Ces deux elements ont migre et sont retrouves dans les horizons sous-jacents du profil etudie, a la difference de As et Pb. Aucune difference significative entre les teneurs des deux materiaux n'a ete mise en evidence pour Pb. Un enrichissement d'un facteur 3 en As a ete constate dans le materiau altere par rapport a son homologue peu altere. Il s'accompagne d'une augmentation des concentrations en fer de l'ordre de 25%. Les neoformations associant Fe et As, identifiees localement, sont des pieges efficaces pour As puisque cet element n'est que peu present dans les horizons sous-jacents. Les donnees recueillies indiquent finalement que le materiau est en cours d'alteration et constitue une source d'elements toxiques dont certains sont mobilisables par un simple echange ionique. L'incidence de la structure du profil sur son evolution geochimique est soulignee.

Landfill deposits of contaminated, dredged sediments are subject to chemical alteration and especially to oxidation processes. Accordingly, sulphides are gradually oxidized leading to the formation of secondary phases and associated metals could become mobile and redistributed among the sediment components, such as carbonates, clay and freshly precipitated (hydr)oxides. Once mobilised, metals could represent a hazard for the environment and especially for drinking water supply facilities.