Displays

Keywords: emerging contaminants, pharmaceuticals, groundwater, karst, boDEREC-CE

Pertaining to the technological advancement of laboratory instruments and analytical methods, an array of questions regarding the occurrence and fate of anthropogenic substances referred to as “Emerging Contaminants” (EC), are brought to light. The term is used not only to describe new compounds, but also for those not perceived as having detrimental effects on the environment and human health. EC such as a wide spectrum of pharmaceuticals and personal care products (PPCP), enter the soil and water mainly through excretion, disposal of waste and wastewater, where they are found in generally low concentrations (ng/I to μg/I). Owing to knowledge gaps on persistency, ecotoxicity, transport and fate, majority of EC are currently not part of a routine surface water/groundwater monitoring programmes on EU level. Interreg Central Europe project boDEREC-CE (Board for Detection and Assessment of Pharmaceutical Drug Residues in Drinking Water – Capacity Building for Water Management in Central Europe) recognized this as an issue that should be addressed by strong transnational cooperation of renowned experts and relevant stakeholders. Thus, the project offers an opportunity for integrated management of waterworks, recommendations for the enhancement of current legislation on drinking and wastewater standards as well as technical solutions. Subsequently, through eight preselected pilot areas across Central Europe grouped in three clusters (groundwater extraction sites, surface water extraction sites, extraction sites in karstic areas), behaviour of EC, natural attenuation and removal efficacy of different treatment techniques will be thoroughly studied via jointly developed monitoring methodology and common project’s EC database.

Jadro and Žrnovnica springs catchment is selected as a Croatian pilot area. This typical Dinaric karstic catchment (250-500 km²), located in the middle part of southern Croatia, supplies with water city of Split and its wider surroundings. Hydrogeological field investigation will be conducted on spring and surface water for analyses of EC, stable isotopes and major ions, including in situ field measurements of physio-chemical parameters. The aim of pilot activities is to identify main EC from the group of PPCP, their behaviour and fate, but also to gain better insight into the complex hydrogeological properties of this karstic catchment, consequently helping to improve protection of drinking water resources and thus human health. Monitoring data gathered through project activities will be an input for testing of models in three pilot cluster, which will help to develop an implementation strategy of a model-based decision making tool for EC called “modePROCON”.

As HGI-CGS participates also in Horizon 2020 project GeoTwinn focused on EC in karst groundwater, a chance for synergy building will enable experts to exchange experience and knowledge gained in the field of EC.

How to cite: Selak, A., Lukač Reberski, J., Terzić, J., Boljat, I., Čapalija, B., Leontić, M., Bulović, B., Patekar, M., and Filipović, M.: Emerging contaminants in water resources of Croatian karst - boDEREC-CE project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-575, https://doi.org/10.5194/egusphere-egu2020-575, 2020.

Because of their environmental recalcitrance, high mobility, and toxicity, poly- and perfluoroalkyl substances (PFASs) are a growing and significant threat to groundwater throughout the world.  There has been progress in the detection and treatment of PFASs, however their transport behavior in the subsurface are still not well understood.  Despite the relative mobility in the subsurface, PFASs have been found in source-zone soils at significant levels even decades after their application ceased. This observation has largely been attributed to both the presence of highly sorptive polyfluorinated precursors to perfluoroalkyl acids (PFAAs) as well as the retention of PFASs at the air-water (A-W) interface.

This paper discusses the general behavior of PFASs in the unsaturated zone and identifies several shortcomings related traditional contaminant transport experimentation and modeling methods when applied to PFASs. To address these issues, significant gaps in understanding related to the conceptualization, testing, and modeling of PFAS behavior in unsaturated zone have to be investigated.  Our preliminary work confirms that PFASs are highly retarded and retained at the A-W interface.  However, when PFAS-based aqueous film forming foams (AFFFs) are used, the mixture of PFASs introduced to the environment is significantly more complex: AFFF formulations can contain hundreds of PFASs in varying concentrations.  Three key findings of our research with respect to PFAS transport in the unsaturated zone are:

1. Current methods of breakthrough curve (BTC) analysis make simplifying assumptions which are likely insufficient for quantifying PFAS retention at the A-W interface. Both the residual air trapping and dead volume impacts are assumed to be negligible in traditional BTC methods. These assumptions are likely ill-suited for PFAS analysis. A more sophisticated understanding and analysis of equilibrium BTCs is proposed for PFASs.
2. Most BTC analysis in past studies is often conducted using short (less than 100 cm) columns, on one compound at a time with gravimetric calculations of the degree of saturation of the whole soil sample. End effects create non-uniform saturation along the length of columns. Furthermore, conducting BTC analysis one compound at a time is time consuming. By combining non-targeted chemical analysis with high resolution mass spectrometry (HRMS), BTC analysis can be performed on field-relevant complex mixtures with high accuracy saturation measurements.
3. Equilibrium partitioning is often assumed to describe retention of multi-component compounds. Because unsaturated transport is controlled by capillarity that depends on interfacial tension at A-W interfaces and PFASs are surfactants with unusual transport behavior, it is unlikely that equilibrium transport models will sufficiently describe PFASs transport.  Conceptual models of physical and chemical non-equilibrium transport have been developed and are undergoing field and laboratory verification.

How to cite: Higgins, C., Stults, J., and Illangasekare, T.: Unsaturated Zone Transport and Mobility of PFAS: Experimental Study for New Insights, Conceptualization, and Modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9306, https://doi.org/10.5194/egusphere-egu2020-9306, 2020.

Remediation of sites contaminated with per- and polyfluorinated alkyl substances (PFAS) is key to reduce the contamination of drinking water sources and human exposure. PFAS use is increasingly being restricted worldwide resulting in reduction of point sources; however, legacy plumes are still posing a threat due to the persistence of these chemicals against degradation. One of the most widely studied soil remediation techniques for PFAS is stabilisation (fixation) which results in the long-term entrapment of the contaminants with the addition of activated carbons in the subsurface, aiming to restrict their leaching from soil to groundwater. In relation to this, the aim of this study was to identify the leaching behaviour of various PFAS in a treatment scenario using activated carbons. Silt loam soil sampled from central Sweden was tested, as well as a mixture of the soil with powdered activated carbon (PAC) and colloidal activated carbon (CAC) at 4% w/w concentration. Spiked groundwater was prepared with 21 PFAS, at a concentration of 2.4 μg mL^-1 for each individual compound. The leaching of PFAS from the solid phase was simulated using column experiments in saturated conditions. Additionally, the partitioning behaviour of the substances with increasing concentration was studied through the definition of sorption isotherms for each matrix. For this purpose, batch-shaking tests were performed, and sorption isotherms were defined by fitting the data with the Freundlich and Langmuir models, using five concentration points in the range of 0.1-100 μg mL^-1 for the sum of PFAS. Analysis of the compounds was conducted using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Preliminary results from the batch tests show significantly increased sorption in soil amended with activated carbons compared to the untreated soil and a better overall performance of CAC compared to PAC. The study is expected to provide essential information on the efficiency and longevity of stabilisation with activated carbons as a remediation strategy for PFAS-contaminated soils.

How to cite: Niarchos, G., Georgii, L., Berggren Kleja, D., Ahrens, L., and Fagerlund, F.: Column experiments to investigate the fate of per- and polyfluorinated alkyl substances (PFAS) in the subsurface during soil stabilisation with activated carbons., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-774, https://doi.org/10.5194/egusphere-egu2020-774, 2020.

The presence of ultraviolet filters (UV) in personal and care products, like cosmetics or sunscreens, is quite common. Consequently, they have been found most of water systems (e.g. ocean, river, aquifers). In porous media, the two main processes governing their fate are sorption and degradation. In the case of degradation, it is mainly governed by co-metabolism processes, which means that these molecules are broken due to the presence of more labile organic carbon which facilitate an enzymatic activity in the system. On the other hand, most of UVs are characterized by high . Thus, sorption plays a central role in their fate. In dynamic biological systems, like hyporheic zones, bioremediation sites or Managed Aquifer Recharge facilities, a high amount of microorganisms, forming biofilms, can be found. In this work, we have evaluated the role of biomass as a sorbent of UV-filters. Furthermore, we have also evaluated the importance of redox conditions in the co-metabolic degradation, and thus, the production of biomass. To achieve this general objective, a conceptual and a numerical model were developed. The results of the models were compared with previous published data by Liu et al. (2013), which performed a set of batch experiments to evaluate the fate of UV under different redox conditions. The compounds evaluated were common UV filters: Benzophenone-3, the benzotriazoles (UV-326 and UV-329)), octyl 4-methoxycinnamatte and octocrylene.

How to cite: Sanchez-Vila, X. and Rodriguez-Escales, P.: Evaluating the role of biomass in the sorption of four UV-Filters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19874, https://doi.org/10.5194/egusphere-egu2020-19874, 2020.

Dissolved organic matter (DOM) plays an important role in affecting the environmental behaviors of organic contaminants. Effects of two representative DOMs (dissolved humic acid (HA) and tannic acid (TA)) on sorption of benzotriazole (BTA) to a reference soil were investigated by batch experiments. The results indicated that TA had stronger sorption to soil than HA (initial solution pH=6.0±0.1). This is because that TA contains more carboxylic and phenolic groups than those of HA. In the solution with DOM, the enhanced sorption of BTA was caused by cumulative sorption resulting from sorbed DOM. Hydrogen bonding was proposed as the main binding mechanism between BTA and the sorbed DOM. When the solution pH at sorption equilibrium increased from 6.5 to 10.5, the electrostatic repulsion inhibited the sorption of BTA in solution with/without HA. In addition, less hydrogren bonds made the effect of HA in promoting BTA sorption decrease when solution pH changed from 6.5 to 10.5. Higher molecular weight fractions of HA could be preferentially sorbed by the soil, its enhancement on BTA sorption was more obvious than that of the low molecular weight fractions. These findings are conducive to a better understanding of environmental behaviors of BTA as well as other organic compounds with similar structure in the unsaturated zones.

How to cite: Wu, L., Dai, J., and Bi, E.: Effects of dissolved organic matter on sorption of benzotriazole to soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6229, https://doi.org/10.5194/egusphere-egu2020-6229, 2020.

Permeable reactive barrier (PRB) technology is being introduced as an alternative method for controlling and treating the groundwater, contaminated with heavy metals, chlorinated organics and radionuclides, etc. To regulate the cost of PRB technology to minimum in line with regulatory decontamination requirements for the contaminants, reactive media should be readily available at a low level of moderate cost. The proposed media included Zeolite (Clinoptilolite) and Sepiolite both as natural raw materials. In this work, we propose to investigate an alternative permeable barrier system for controlling and preventing the migration of radio cesium into the groundwater. It is understood that the falling head type vertical permeability tests performed on the reconstituted raw materials in a special odeometer test device under several vertical pressures might be inadequate to model the natural horizontal flow without mechanical assistance through the barrier in the aquifer. The bench- scale PRB demonstration system were also designed to investigate the horizontal 2D flow of groundwater by supplying a constant difference in between total heads of upstream and downstream. The hydraulic conductivity of the saturated media was studied by a flow net analysis. The effect of the simulated continuous release of contaminant solution in the upstream was observed in the soil media not only at the downstream both also in the upstream and PRBs. Remediation process over time can lead to changes in the hydraulic conductivity of a PRB. The bench-scale PRB system will be used to approximate the operating conditions for the information on the transport behavior of the radio cesium andchange in the hydraulic conductivity in PRB system.

How to cite: Cevikbilen, G. and Camtakan, Z.: Bench-scale studies of a permeable reactive barrier system for radiocesium removal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13162, https://doi.org/10.5194/egusphere-egu2020-13162, 2020.

A large number of sites worldwide are subjected to contamination by dense non-aqueous phase liquids (DNAPLs). This group of typically highly persistent chemicals arise tremendous threats to ecosystems and humankind, especially for groundwater abstraction and usage. In particular, chlorinated solvents have great risk profiles due to their toxic and carcinogenic properties, posing essential needs for appropriate risk assessment and site management strategies. Once released into the subsurface, DNAPLs form so-called source zone geometries (SZGs), i.e., physical shapes containing multiple phases, which represent long-term sources for contamination of downstream groundwater. The complex geometrical and chemical properties of such sources are, together with subsurface characteristics and hydraulic conditions of the aquifer, the most sensitive factors in controlling contaminant plume propagation. As locations of DNAPL sources are widely unknown and subsurface phase exploration methods are limited by technical and financial constraints, in most site assessments, dissolved contaminant plumes are detected only. This fact has led to numerous sites where remediation efforts have been inefficient or even failed, or exceeded economical pre-calculations. Here, improved knowledge on factors controlling source zone formation would lead to better predictions for corresponding SZGs and, therefore, better estimations of contaminant plume evolution and prediction.

A quasi-two-dimensional tank setup formed the basis for generating experimental measurement data of DNAPL migration and entrapment at a Darcy scale under defined laboratory conditions. Three different types of single-size fraction materials (glass beads, filtering glass, and natural sand) were used as homogeneous porous media. DNAPL release into the initially fully water-saturated tank was realized by means of a falling-head boundary condition. Both the aqueous and non-wetting phases were marked for better optical visibility using colorization tracers. All experimental scenarios were conducted under equal ambient conditions (e.g., constant temperature, homogeneous light source). Raw data collection was performed by serial image acquisition from one tank side. A set of customized image analysis and processing approaches was used for the automatized calculation of DNAPL saturation distributions, which served as experimental data for calibrating the base case model scenarios.

For each base case scenario, a representative numerical multiphase flow model was set up using the software codes TMVOC and OpenGeoSys. Starting parameters for calibration were selected based on the tank layout, technical data sheets and hydraulic characterization of the porous media. Each model setup was then run with a specified range of variation for each parameter after successful calibration, whereby parameter ranges were chosen to coincide with physically plausible values at laboratory scale. Through this semi-automatized parameter sensitivity analysis, controlling factors of source zone formation could be identified and ranked along their strength of impact on SZGs. Furthermore, the comparison between results of each software code could identify strengths and weaknesses of each one.

How to cite: Engelmann, C., Sookhak Lari, K., and Walther, M.: The Relevance of Fluid and Porous Media Properties for DNAPL Migration and Entrapment: A Numerical Evaluation of Laboratory Experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6347, https://doi.org/10.5194/egusphere-egu2020-6347, 2020.

Pharmaceutically active compounds have increasingly been detected in groundwater worldwide. Despite constituting a major risk for ecosystems and human health, their fate in the environment has still not been thoroughly investigated. This study characterizes the transport behavior of five selected pharmaceutically active compounds (antipyrine, atenolol, caffeine, carbamazepine and sulfamethoxazole) in two sediments (coarse quartzsand and sandy loam) using column experiments with long-term injection of spiked groundwater accompanied by monitoring of microbial activity in the columns. Transport parameters were estimated using an analytical reactive transport model. When five selected compounds were injected simultaneously, transport behavior of antipyrine, carbamazepine and the antibiotic sulfamethoxazole were similar to the conservative tracer in both sediments and under varying redox conditions. During the entire duration of the experiments of about two months no degradation was observed, thus showing the low potential for natural attenuation. Atenolol and caffeine were subject to retardation which was significantly stronger in the sandy loam sediment compared to the coarse quartzsand. This was attributed to higher contents in clay and organic carbon in sandy loam. Biodegradation of caffeine was observed in three out of four non-sterilized settings after an adaption period of 120 to 420 hours and was dependent on the presence of dissolved oxygen. Atenolol was biologically degraded in the coarse quartzsand while the type of degradation remained unclear in the sandy loam sediment. The identification of biodegradation processes was supported by monitoring of intracellular adenosine triphosphate (ATP_itc) as a measure for microbial activity. ATP_itc was present in varying concentrations in all sediments with higher concentrations when degradation of pharmaceuticals, especially caffeine, was observed. When only caffeine and sulfamethoxazole were injected simultaneously, sulfamethoxazole was degraded while caffeine was not. The latter seems to be influenced by low concentrations in dissolved oxygen rather than the presence of the antibiotic sulfamethoxazole. Results of these experiments emphasize the impact of sediment type and redox conditions on pharmaceutical transport as well as the effect of combination and variety of pharmaceuticals that are released together into the environment.

How to cite: Schübl, M., Kiecak, A., and Stumpp, C.: Sorption and Degradation of Selected Pharmaceuticals in Controlled Laboratory Column Experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5445, https://doi.org/10.5194/egusphere-egu2020-5445, 2020.

Recent investigations show presence of anthropogenic substances in surface and groundwater at relatively low concentrations, which nevertheless represent a potential risk to our environment and health. These substances are emerging contaminants, which are synthetic or of natural origin and include: pharmaceuticals, pesticides, industrial chemicals, surfactants and personal care products. Emerging contaminants are currently very rarely or not at all included in regular monitoring of water bodies.

The boDEREC-CE project deals with the problem of the presence of modern pollutants with the aim of establishing a management strategy for waterworks that guarantees increased quality of drinking water. The project is exploring innovative approaches for monitoring emerging contaminants in 8 pilot action areas in 7 Central European countries.

The Slovenian pilot action area is the Ljubljana Basin; with an area of 815 km² is the largest closed plane in the country. The basin with its central position represents the most important urban, economy and traffic area in Republic of Slovenia where the main roads and rail connection converge. A total of 40% of Slovenian population lives here.

In comparison to forest and semi natural areas, which cover 22% of the basin, the Ljubljana Basin is mostly covered by areas with activities that may introduce new pollutants into the environment, such as agricultural areas, which cover 55% and artificial surfaces, which cover 20% of the basin. The latter present potential sources of emerging contaminants, such as: sewage network, emissions from industrial facilities, wastewater treatment plants and landfills.

The Ljubljana basin is an important drinking water resource for several cities and other settlements. Drinking water protection zones that protect drinking water sources cover almost a quarter (24%) of the Ljubljana Basin.

In order to develop an innovative approach for monitoring such pollutants in the pilot action area, sampling of surface water (8 sampling points) and groundwater (9 sampling points) is carried out in two phases. In the first phase, passive sampling is carried out with active carbon inserted into a stainless steel mesh, which is installed in a location for approximately 3 months. After collecting the passive samplers, active carbon is dried and the pollutants adsorbed are eluted with dichloromethane. Passive sampling is an analytical method for the qualitative determination of organic pollutants and serves as a preliminary step for the second phase, which represent active sampling by grab samples of surface and groundwater.

The boDEREC-CE project is not only focusing on the direct study of the behavior of emerging contaminants in the aquatic environment, but also on assessing the effectiveness of reducing the pollution. In addition, activities to inform the public about measures to reduce waste of emerging contaminants will be organized.

How to cite: Jelovčan, M., Auersperger, P., Brenčič, M., Bračič Železnik, B., Pucihar, B., Torkar, A., and Vidmar, I.: Detection and assessment of the emerging contaminants in the Ljubljana Basin, Slovenia – preliminary report, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8009, https://doi.org/10.5194/egusphere-egu2020-8009, 2020.

Determining the transport characteristics of pollutants in a gravel unsaturated zone is particularly difficult, owing to the heterogeneity of the geological media. Understanding the mechanisms and rates of movement of pollutants in the unsaturated zone is an important issue in the process of groundwater protection. One of the most valuable ways of investigating the characteristics, groundwater flow and solute transport in the unsaturated zone is by conducting experimental research, namely tracer experiments. Flow and transport parameters of propyphenazone, caffeine and carbamazepine have been studied with tracer experiments using a lysimeter facility in the Selniška Dobrava (NE Slovenia). The lysimeter site is designed as a field laboratory. The dimensions are 2x2 m, 5 m deep, with 0.2 m thick walls. There are 10 sampling and measuring points at different depths (from JV-1 to JV-10) with approximately equal distances in depth. For the purpose of sampling groundwater in the unsaturated zone, drainage samplers were installed and connected to a water sampling system. The tracer experiment lasted over a time period of approximately two years. The organic pollutants selected to determine the processes of migration and degradation through the aquifer were carbamazepine, propyphenazone and caffeine. Compounds differ in their physical and chemical properties, which results in different transport paths and velocities of individual pollutants through the aquifer. Due to its conservative behaviour, deuterated water was used as the conservative tracer. For the evaluation of flow and transport parameters the HYDRUS 1-D software was used. In the conference contribution, modelling and estimation of hydraulic properties of the soil and selected pharmaceuticals within a coarse gravel unsaturated zone will be presented.

How to cite: Koroša, A., Brenčič, M., and Mali, N.: Sorption and degradation of pharmaceuticals in the unsaturated zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22431, https://doi.org/10.5194/egusphere-egu2020-22431, 2020.

Micro-organic (MO) compounds have been recognized as an important factor in environmental pollution. Developments in a range of analytical techniques are expanding the number of MOs that can be detected in groundwater. They may not be new contaminants, but recently detected using improved sampling and analytical methods. Monitoring programmes for groundwater are largely based on the collection of grab (spot) samples. One of the methods to determine the presence of organic compounds in groundwater v can also be passive sampling. Contrary to grab sampling, passive sampling is less sensitive to accidental extreme variations of the organic compounds concentrations in groundwater and it also allows determination of a large range of contaminants at once. A passive sampler can cover a long sampling period, integrating the pollutant concentration over time. This paper presents the application of the passive sampling technique for monitoring organic pollutants within the four major alluvial aquifers in Slovenia used for water supply. Passive samples were analyzed by gas chromatography mass spectrometry (GC-MS). For the interpretation of chromatograms, the AMDIS deconvolution was used. The deconvolution was covered by the GC-MS library with retention times for 921 organic contaminants from Agilent USA, as well as by the NIST 2008 library of mass spectra. Most frequently detected MO substances were classified in different pollutant groups with respect to their origin (urban source, agriculture or industry). Based on the results, a comparison of the presence of MOs in the present aquifers was made. Passive sampling with active carbon fibres was proved to be an appropriate method for monitoring micro-organic pollutants in groundwater.

How to cite: Mali, N., Koroša, A., and Auersperger, P.: Passive sampling as a tool for determination of micro-organic compounds in groundwater resources , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22436, https://doi.org/10.5194/egusphere-egu2020-22436, 2020.

Landfill leachate, a highly contaminated percolating effluent can cause a considerable threat to human as well as environmental health. We developed a novel nano composite using the polymer encapsulated magnetic geopolymer for efficient removal of multi contaminants (As, Zn, Fe, Co, Cu, Ni, Pb, F, NO 3 - , and PO 4 3- ) present in the landfill leachate and groundwater of the Pirana solid waste dumping site, Ahmedabad, Gujarat. A series of batch and column sorption experiments were carried out to find the best-operating conditions for optimum removal efficiency. Results revealed that in the range of 50-60% of multi-contaminant removal is possible using the newly developed adsorbent which has high surface area as well as mixed functional groups for the removal of both cationic (Zn, Fe, Co, Cu, Ni, and Pb) and anionic (F, NO 3 - , and PO 4 3- ) contaminants present in the leachate. Batch study shows that both physical and chemical sorption are equally operational and multilayer removal following the Freundlich isotherms predominantly. The batch test mimics the equilibrium condition only. The study recommends column study under different follow conditions using leachate and groundwater, followed by a regeneration study for its reusability and development of the field implementation schemes. The future research is required to address the decontamination of emerging contaminants like pharmaceuticals, pesticides and fertilizers, industrial additives and antibacterial agents.

How to cite: Pradhan, N. and Kumar, M.: Development of magnetic nano-geocomposite for groundwater and leachate treatment: A Landfill Management Perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22425, https://doi.org/10.5194/egusphere-egu2020-22425, 2020.

Per- and polyfluorinated alkyl substances (PFASs) are extremely recalcitrant contaminants that pose a challenge for remediation in soil and groundwater due to their chemical stability and resistance to degradation. They are used in numerous consumer products and their use in firefighting aqueous-film-forming foams has led to worldwide contamination of groundwater resources associated with airports and firefighting training areas. One of the currently most promising in-situ treatment techniques is stabilization using activated carbon (AC) sorbents that can immobilize PFASs in the soil and prevent further spreading from a contaminated site. However, few documented field studies exist.

In this study we investigated in-situ stabilization of PFASs by injection of colloidal activated carbon (CAC, PlumeStop®) at a PFAS contaminated site in Arboga, Sweden. Prior to the design of the pilot-scale test and CAC injection, the geology and state of contamination were carefully characterized and PFAS concentrations and groundwater levels were monitored continuously for almost one year. CAC was injected to create a defined zone of PFAS-sorption where PFASs from the contaminant plume would be sorbed to CAC and removed from the flowing groundwater, similar to a permeable reactive barrier. The effect of the injected CAC was studied by monitoring PFAS concentrations in the groundwater up- and down-gradient as well as within the CAC barrier both before and after injection. General water chemistry and groundwater levels were also monitored.

The site characterization showed that there are two distinct source zones of PFAS contamination with different contamination signatures. Continuous baseline monitoring prior to CAC injection did not show any major changes in PFAS concentrations, but revealed seasonal variations in the groundwater levels and flow patterns, leading to seasonal changes also in the direction of contaminant transport. The CAC injection pilot-scale test was therefore designed to shield the down-gradient evaluation wells in small part of the plume accounting for seasonal changes. The geological setting of the site mainly is clayey till soil of relatively low hydraulic conductivity on top of crystalline bedrock, but there are also high permeability flow paths. The low-pressure CAC injections were hence designed and adapted to avoid excessive preferential flow of CAC and achieve a good distribution of CAC in the intended treatment zone (barrier).

Preliminary results from the monitoring showed strong reduction of all measured PFASs within and directly down-gradient of the CAC barrier. These results indicate that the installation of the CAC barrier was successful despite a relatively complex geological setting where fast preferential flow paths exist. The continuing monitoring will show how the CAC performs over time.

How to cite: Fagerlund, F., Niarchos, G., Ahrens, L., Berggren Kleja, D., Bergman, J., Larsson, A., Leonard, G., Forde, J., Edvinsson, J., Holmström, K., Persson, H., and Gottby, L.: Pilot-scale injection of colloidal activated carbon for PFAS immobilization at a contaminated field site, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17615, https://doi.org/10.5194/egusphere-egu2020-17615, 2020.

This study was performed to understand dense non-aqueous phase liquid (DNAPL) persistence by the back diffusion from the three types of clay using one-dimensional analytical solutions. The conceptual model was designed with 5 m thickness of an aquifer underlain by 0.7 m thickness of an aquitard. The aquitard was considered to be a finite domain boundary at the bottom of bentonite (B), kaolinite (K), and montmorillonite (M) layers. The tortuosity of each clay was assumed to be 0.95 (B), 0.55 (K), and 0.05 (M). A diffusion model scenario assumed a step change in concentration boundary condition representing complete removal of trichloroethylene (TCE) and tetrachloroethylene (PCE) at the source zone, after 10 years of source loading. Total accumulated mass in the aquitard during the forward diffusion showed that PCE was 57.3 (B), 44.3 (K), 13.3 (M) g/m², and TCE was 329.2 (B), 256.2 (K), 76.8 (M) g/m². The calculated tailing concentration of PCE at the aquifer during the back diffusion maintained higher concentrations than the maximum contaminant level (MCL, PCE = 5 μg/L) for 22 (B), 16 (K), and 11 (M) years, respectively, in the same order as the tortuosity of clays. The calculated tailing concentration of TCE above MCL (TCE = 5 μg/L) was maintained for 38 (B), 43 (K), and 19 (M) years. These results showed that the total accumulated mass of TCE was higher in the bentonite layer than the kaolinite layer, but the TCE tailing concentrations caused by back diffusion from the kaolinite layer maintained 5 years longer above MCL than those caused by back diffusion from the bentonite layer due to different values of tortuosity for bentonite and kaolinite. The results of this study indicate that the tortuosity of clays has a significant influence on plume persistence caused by back diffusion.

How to cite: Jang, S. and Yang, M.: TCE and PCE plume persistence based on different clay types, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21205, https://doi.org/10.5194/egusphere-egu2020-21205, 2020.

The presence of contaminated aquitards has been recognized as one of the main obstacles that hamper the successful aquifer restoration and the forward and back diffusion processes were known as the primary mechanism of solute exchange between the aquifer-aquitard system. In this study, a series of 2-D flow chamber experiments were conducted using 1 g/L of bromide solution as a non-reactive tracer to evaluate back diffusion phenomenon and plume tailing behavior based on different clay types (kaolinite, montmorillonite, and bentonite). In order to determine appropriate values for clay tortuosity, simulated effluent concentrations using 1-D analytical solutions were compared to the measured effluent concentrations. The best fits were found with for bentonite, for kaolinite, and The bentonite tortuosity value close to 1 indicates that the solute flowpath is similar to the aquitard straight-line distance under the saturated condition. Simulation results using the calculated tortuosity showed that bromide effluent concentration due to back diffusion from the montmorillonite layer decreased to 3 orders of magnitude below the initial concentration after 60 days of back diffusion. For bentonite, calculated effluent concentrations decreased to 3 orders of magnitude below the initial concentration after 230 days of back diffusion. These results suggest that the aquitard with higher tortuosity has more capability to sustain long-term plume persistence for non-reactive contaminants and more potential risks as secondary contaminant sources.

How to cite: kim, C. and yang, M.: The effect of clay tortuosity on contaminant plume persistence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21203, https://doi.org/10.5194/egusphere-egu2020-21203, 2020.

Batch adsorption experiments were performed to investigate influences of experimental conditions such as initial uranium concentrations (0, 1 x 10^-3, 1 x 10^-2, 0.1, 0.5, 1 mg/L) and pHs of solution (4, 7 and 9.5) on uranium adsorption in three types of clay (kaolinite, montmorillonite, and bentonite). For all experiments, the adsorption of uranium could be described by the linear isotherm model at solution concentrations less than 1 mg/L, showing high values of correlation coefficient (R2 > 0.98). The adsorption efficiencies of montmorillonite and kaolinite for all pHs are more than 91% and 87%, respectively. The effect of pH on the adsorption of uranium was not found in kaolinite and montmorillonite for all initial concentrations. However, the adsorption efficiency of bentonite was lower than other clay types (< 75%). Solutions with low initial concentrations (< 1 x 10^-2 mg/L) achieved high efficiencies for adsorption of uranium (> 99%) at all pHs, while low efficiencies were observed in solutions with high initial concentrations (> 0.1 mg/L) at pH 4 (47%), pH 7 (59%) and pH 9.5 (43%). It is concluded that montmorillonite and kaolinite can be used as an effective adsorbent for removing uranium from aqueous solutions.

How to cite: Kim, S. and Yang, M.: Influence of initial concentrations and pH conditions on uranium adsorption in clays, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21163, https://doi.org/10.5194/egusphere-egu2020-21163, 2020.

Uranium (U) is a naturally occurring radionuclide that poses serious health risk owing to its chemical and radiological toxicity. The main route of U exposure towards humans is drinking (ground)water. The mobility of U is essentially driven by its speciation, where U(VI) is present as relatively mobile species and U(IV) as largely immobile in the environment. Hence, many U remediation strategies are targeted towards biotic or abiotic reduction of U(VI) to immobile U(IV) species. However, success of such remediation processes is dependent on biogeochemical conditions caused by interactions between dissolved species, mineral surfaces, and microbial activities. Protecting water quality thus requires better understanding of the geochemical factors that control U stability in the subsurface environment; one such factor is the presence of organic ligands.

            The role of naturally occurring organic ligands in affecting nutrient and contaminant mobility is well established in subsurface environments. We tested the hypothesis that these organic ligands have the potential to effectively remobilize the reduced uranium and bring it to a concentration that exceeds the WHO safety guideline for U in drinking water (30µg L^-1). We utilized aquifer sediment from Retz, Austria in which uranium bioreduction is known to occur. Bioreduction and accumulation of dissolved U was observed in a flow through column experiment. These reduced U containing sediments were then treated with various organic ligands (e.g., citrate, oxalate, EDTA, DTPA, and DFO-B) in varying concentrations in batch and column experiments to elucidate the mechanism and extent of ligand-induced mobilization of U. We also used geochemical modelling with PhreeqC to generate a conceptual model for ligand-induced mobilization of U.

            The results of this study provide insights in the extent of ligand-induced mobilization of U in the environment. This information is essential in planning future aquifer management and U remediation strategies

How to cite: Alvarez Salas, M. A., Chardi, K., Schenkeveld, W., Kumar, N., Giammar, D., and Kraemer, S. M.: Immobilization and ligand-induced remobilization of uranium in anoxic aquifer environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15654, https://doi.org/10.5194/egusphere-egu2020-15654, 2020.

Oil refinery industry historically has been related with groundwater pollution. According to WHO, contaminants may reach groundwater most easily as a result of discharge to the ground surface and subsequent infiltration through the soils, or releases from the ponds. Environmental Performance Review for Kazakhstan from UNECE states that oil refinery factories in Kazakhstan are one of the biggest sources of groundwater contamination despite of existing governmental and industry environmental monitoring systems. Recent studies showed that more than 50% of the people in rural Kazakhstan use groundwater for domestic purposes, consequently, many people potentially drink unsafe water. Despite this, oil refineries in Kazakhstan continue to discharge wastewater with high concentrations of different pollutants and these contaminants reach the groundwater very easily. The aim of this paper is to analyse and interpret a dataset obtained during a 6-year (2014–2019) monitoring program of the control of groundwater quality surrounding recipient of poorly treated wastewater discharges in one of the Kazakhstani industrial clusters. Multivariate statistical techniques and Heckman selection model were used for assessment of loading of natural and anthropogenic contribution to contamination, including separated evaluation of the impact of toxic substances.

The results show that PCAs have high loading of anthropogenic contamination to groundwater from the oil refinery industry coupled with natural geochemical processes. High concentrations of several parameters, such as total petroleum hydrocarbons, phenols, sodium, chlorides, sulphates, total dissolved solids and total hardness were identified. Water containing such exceeding concentrations of substances affects human body significantly and normally is considered to be rejected by consumers. By means of cluster analysis, the examined wells were combined in three groups according to the concentrations of chemicals and their locations. The results enable a prediction of the groundwater flow in the region studied as well as an estimation of which sites would be most severely affected by contamination. According to obtained data from Heckman analysis, focus of further research should be paid to the distribution of toxic contaminants. The industry is continuing to pollute the environment, which means that assessment of existent and future hazards is needed through improved monitoring system. Thus, the next step of the research considers contamination transport modelling for definite identification of groundwater flow and potentially affected rural areas.

How to cite: Radelyuk, I., Tussupova, K., and Zhapargazinova, K.: Impact of oily wastewater for public health in rural area: a case study of Kazakhstan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11235, https://doi.org/10.5194/egusphere-egu2020-11235, 2020.