Multitracer experiment to evaluate the attenuation of selected organic micropollutants in a karst aquifer

A modified and rapid method for the single-well push-pull (SWPP) test using SF6, Kr, and uranine tracers

In the present study, a single-well push-pull (SWPP) test was conducted with multi-component tracers, including inert gas (SF₆ and Kr) and uranine (conservative), to understand the volatile/semi-volatile component transport characteristics in the groundwater system. In an SWPP test, it is essential to obtain an initial breakthrough curve (BTC) of the inert gas concentration at the beginning of the pulling stage to analyze the hydraulic properties of the groundwater system. As a result of the SWPP test using a proposed method in this study, physicochemical parameters of the groundwater and BTC of gas tracers and uranine were acquired simultaneously and successfully. In addition, on-site measurements of uranine, pCO₂, and water quality data, such as electrical conductivity (EC), temperature, pH, and dissolved oxygen, were undertaken. Modification of an existing pCO₂ measuring system allowed the gas samples to be collected, transported, and analyzed for inert gas components within a few hours. As a result, reliable and interpretable data with a recovery ratio of 26%, 85%, and 95% for SF_6, Kr, and uranine, respectively, were obtained. The differences in the recovery ratio were utilized to identify the environmental system, whether it contains gas inside the isolated system (closed) or not (open), and to understand plume behavior characteristics in the experimental zone. By applying a two-dimensional advection-dispersion model to the acquired tracer test data and comparing the observed and computed tracer concentrations, helpful information was obtained on the hydraulic and transport characteristics of the targeted zone. This method can be extended to the design of dissolved CO₂ transport monitoring of an aquifer above a CCS site.

Acesulfame allows the tracing of multiple sources of wastewater and riverbank filtration

Aquifers providing drinking water are increasingly threatened by emerging contaminants due to wastewater inputs from multiple sources. These inputs have to be identified, differentiated, and characterized to allow an accurate risk assessment and thus ensure the safety of drinking water through appropriate management. We hypothesize, that in climates with seasonal temperature variations, the sweetener acesulfame potassium (ACE) provides new pathways to study wastewater inputs to aquifers. Specifically, this study investigates the temperature-driven seasonal oscillation of ACE to assess multiple sources of wastewater inputs at a riverbank filtration site. ACE concentrations in the river water varied from 0.2 to 1 μg L^-1 in the cold season (T < 10 °C) to 0-0.1 μg L^-1 in the warm season (T > 10 °C), due to temperature-dependent biodegradation during wastewater treatment. This oscillating signal could be traced throughout the aquifer over distances up to 3250 m from two different infiltration sources. A transient numerical model of groundwater flow and ACE transport was calibrated over hydraulic heads and ACE concentrations, allowing the accurate calculation of mixing ratios, travel times, and flow-path directions for each of the two infiltration sources. The calculated travel time from the distant infiltration source was of 67 days, while that from the near source was of 20 days. The difference in travel times leads to different potential degradation of contaminants flowing into the aquifer from the river, thus demonstrating the importance of individually assessing the locations of riverbank infiltration. The calibrated ACE transport model allowed calculating transient mixing ratios, which confirmed the impact of river stage and groundwater levels on the mixing ratio of the original groundwater and the bank filtrate. Therefore, continuous monitoring of ACE concentrations can help to optimize the management of the water works with the aim to avoid collection of water with very short travel times, which has important regulative aspects. Our findings demonstrate the suitability of ACE as a transient tracer for identifying multiple sources of wastewater, including riverbank filtration sites affected by wastewater treatment plant effluents. ACE seasonal oscillation tracking thus provides a new tool to be used in climates with pronounced seasonal temperature variations to assess the origins of contamination in aquifers, with time and cost advantages over multi-tracer approaches.

Mixing Controlled Adsorption at the Liquid-Solid Interfaces in Unsaturated Porous Media

The unsaturated zone, located between the soil surface and the phreatic level, plays an important role in defining the fate of any substance entering the subsoil. In addition to the processes of flow and transport taking place in the liquid phase, surface reactions such as adsorption to the solid phase may occur and increase the residence time of the substance entering the system. In this study, we aim to understand the pore-scale mechanisms that control adsorption in unsaturated systems. We combine 2D pore-scale experimental images with numerical simulations to analyze flow, transport, and adsorption under different liquid saturation degrees. We demonstrate the role of mixing on adsorption at the liquid-solid interfaces by analyzing the deformation in time of a pulse-injected surfactant. We also analyze the impact of the isotherm functional shape and the inclusion of the liquid-gas interfaces as adsorption sites on this surface reaction. The enhancement of mixing as saturation decreases is accompanied by a reduction in the amount of adsorbed mass, located mainly along preferential flow paths, where the solute is primarily transported. For the same isotherm, a nonlinear behavior of adsorption as a function of liquid saturation has been observed. This is explained by the nonlinear variation of the volume fraction of liquid behaving as preferential path or stagnation zone as liquid saturation decreases, despite the linear decrease in the surface area of solids accessible for adsorption.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11242-022-01747-x.

Transport-based source tracking of contaminants in a karst aquifer: Model implementation, proof of concept, and application to event-based field data

Identification and location of contamination sources is crucial for water resource protection - especially in karst aquifers which provide 25% of the world´s population with water but are highly vulnerable to contamination. Transport-based source tracking is proposed and verified here as a complementary approach to microbial and chemical source tracking in karst aquifers for identifying and locating such sources of contamination and for avoiding ambiguities that might arise from using one method alone. The transport distance is inversely modelled from contaminant breakthrough curves (BTC), based on analytical solutions of the 1D two-region non-equilibrium advection dispersion equation using GNU Octave. Besides the BTC, the model requires reliable estimates of transport velocity and input time. The model is shown to be robust, allows scripted based, automated 2D sensitivity analyses (interplay of two parameters), and can be favourable when distributed numerical models are inappropriate due to insufficient data. Sensitivity analyses illustrate that the model is highly sensitive to the input time, the flow velocity, and the fraction of the mobile fluid region. A conclusive verification approach was performed by applying the method to synthetic data, tracer tests, and event-based field data. Transport distances were correctly modelled for a set of artificial tracer tests using a discharge-velocity relationship that could be established for the respective karst catchment. For the first time such an approach was shown to be applicable to estimate the maximum distance to the contamination source for coliform bacteria in karst spring water combined with microbial source tracking. However, prediction intervals for the transport distance can be large even in well-studied karst catchments mainly related to uncertainties in the flow velocity and the input time. Using a maximum transport distance is proposed to account for less permeable, "slower" pathways. In general, transport-based source tracking might be used wherever transport can be described by the 1D two-region non-equilibrium model, e.g. rivers and fractured or porous aquifers.

Hydrochemical environment of a fractured karst aquifer influenced by petroleum hydrocarbons

A fractured karst aquifer polluted by petroleum hydrocarbons (PH) for several decades was selected to study the influences of PH on the hydrochemical environment. The research was implemented using the hydrochemical indicators (Ca2+, Mg2+, Na++K+, HCO3-, NO3-, Cl-, F-, and SO42-) and PH with the help of GIS and origin platforms, statistical analyses, and graphical methods. Results showed that PH had significant influences on the hydrochemical environment over the last several decades. The main principle elements influencing the evolution processes of hydrochemical environment were carbonates dissolution, leaking wastewater, and biodegradation processes from 1977 to 2019, and hydrochemistry types changed from HCO3-Ca-Mg and HCO3-Ca to HCO3-Cl-Ca-Mg and HCO3-Cl-Ca. The contribution rate of PH biodegradation to the representative ion increased at first, then decreased over time, which has a close relationship with the variation characteristics of PH. The dynamic evolution processes of hydrochemical environment have significances for indentifying the influencing mechanisms of hydrogeochemical reactions, which could provide valuable scientific suggestions for the local administrators to take effective efforts to optimize and protect the karst groundwater environment.

Contamination characteristics of chlorinated hydrocarbons in a fractured karst aquifer using TMVOC and hydro-chemical techniques

In this study, we investigated a fractured karst aquifer polluted by chlorinated hydrocarbons to determine the contamination characteristics of the main hydrocarbon components. The natural attenuation processes of representative components were simulated and forecasted using TMVOC and hydro-chemical components (NO₃^-, SO₄^2-, HCO₃^- Cl^- and δ¹³C_DIC). The impact of hydrocarbon compounds on the hydro-chemical ions were estimated, and their historical contamination characteristics were also reconstructed. Results showed that the dynamic characteristics of Trichloromethane and 1,1,2-Trichlorethane can indicate those of chlorinated hydrocarbons, where the rate of natural attenuation was observed to decrease with decreasing concentrations of hydrocarbon compounds. Additionally, the long-term variation characteristics in groundwater levels showed that the relatively stable hydrodynamic field conditions enabled the simulation of the natural attenuation processes of chlorinated hydrocarbons. The simulation which also considered the biodegradation processes showed that the use of TMVOC and hydro-chemical parameters may better describe natural attenuation processes. Over 3 years (from 2017 to 2019), the average percentage of biodegradation in the total natural attenuation was estimated to be 88.35%. Similarly, Trichloromethane and 1,1,2-Trichlorethane are forecasted to have no health hazards in 10 and 15 years, respectively. The contribution rates of biodegradation to HCO₃^- and Cl^- in the fractured karst aquifer varied with the concentrations of chlorinated hydrocarbons. Overall, the findings and methods in this work have significant contributions for advancing remediation developments of petroleum hydrocarbons, especially in karst environments that are highly susceptible to contamination.

Contamination and natural attenuation characteristics of petroleum hydrocarbons in a fractured karst aquifer, North China

A rare super-large fractured karst aquifer located in Zibo city, Shandong Province of Northern China was polluted by petroleum hydrocarbons from a petrochemical company. Over the last 30 years, it has been the focus of several remediation efforts. In this study, the contamination and natural attenuation characteristics of the petroleum hydrocarbons were elucidated using hydrogeochemical indicators (DO, DOC, Cl^-, HCO₃^-, pH, NO₃^-, and SO₄^2-), petroleum hydrocarbons elements and environmental isotopes (δ¹⁵N_NO3, δ¹⁸O_NO3, δ¹³C_DIC, and δ¹³C_DOC). With the aid of GIS, statistical analyses, as well as first-order decay model and electron-acceptor-limited kinetic model, the spatio-temporal evolution characteristics of the petroleum hydrocarbons were modeled. Results showed a positive natural attenuation trend over the last 3 decades where intrinsic biodegradation mechanism was found to be the most important factor driving the degradation of hydrocarbons in the aquifer system. The hydrogeochemical association between the indicators and petroleum hydrocarbons provided the evidences of biodegradation and also served as markers, highlighting the occurrence of anaerobic respiration without methanogenic activities within the heterogenous karst media. Furthermore, the mean natural attenuation rate of petroleum hydrocarbons was calculated to be 3.76 × 10^-3/day whereby the current highest petroleum hydrocarbons concentration (361.13 μg/L) is estimated to be degraded completely in 6 years under the present hydrogeological and environmental conditions.

Solute Reactive Tracers for Hydrogeological Applications: A Short Review and Future Prospects

Tracer testing is a mature technology used for characterizing aquatic flow systems. To gain more insights from tracer tests a combination of conservative (non-reactive) tracers together with at least one reactive tracer is commonly applied. The reactive tracers can provide unique information about physical, chemical, and/or biological properties of aquatic systems. Although, previous review papers provide a wide coverage on conservative tracer compounds there is no systematic review on reactive tracers yet, despite their extensive development during the past decades. This review paper summarizes the recent development in compounds and compound classes that are exploitable and/or have been used as reactive tracers, including their systematization based on the underlying process types to be investigated. Reactive tracers can generally be categorized into three groups: (1) partitioning tracers, (2) kinetic tracers, and (3) reactive tracers for partitioning. The work also highlights the potential for future research directions. The recent advances from the development of new tailor-made tracers might overcome existing limitations.

Qualitative and quantitative use of micropollutants as source and process indicators. A review

Nowadays, micropollutants such as pharmaceuticals, pesticides and personal care products can be found ubiquitously in the anthropogenically influenced water cycle. As micropollutants have virtually no natural background concentrations they are significantly more sensitive in detecting processes and flow paths than classic inorganic tracers and indicators and at the same time they are often highly source specific. Therefore, using micropollutants as environmental indicators for anthropogenic activities is a common and frequently applied method today. As they interact in many ways with environmental matrices they can be used for source apportionment as well as to estimate flow paths and residence times in waterbodies. This review gives a systematic overview over the large variety of micropollutants used as indicators in the aquatic environment over the last decades together with the prerequisites on their use. Their application is subdivided into their qualitative (compound presence or absence) and quantitative (volume flows) use and shows the numerous possibilities from gaining basic information on the water regime up to advanced applications such as wastewater-based epidemiology.

Antibiotics in a typical karst river system in China: Spatiotemporal variation and environmental risks

Karst aquifers are highly susceptible to contamination because compounds in water from the land surface are able to enter aquifers directly through sinkholes and travel rapidly through conduits. To investigate the occurrence and profiles of antibiotics in the typical karst river system in Kaiyang, southwest China, 34 aqueous samples were collected periodically to delineate seasonal trends in antibiotic levels. Thirty-five antibiotics, including nine sulfonamides, four tetracyclines, five macrolides, 16 quinolones and chloramphenicol, were analysed via solid phase extraction combined with ultra-performance liquid chromatography-tandem mass spectrometry. A total of 25 antibiotics were detected with the highest detection frequency reaching 94.1%, indicating the ubiquity of antibiotics in the study area. The total concentration of antibiotics ranged from 0.37 to 508.6 ng/L, with the dominating proportion including macrolides and quinolones based on the distribution profiles and seasonal variation. Due to the natural attenuation, the total concentration of antibiotics gradually decreased with the flow direction in the southern part of the river. The total concentrations of antibiotics in the mainstream were significantly higher in the dry season than in the rainy seasons. However, the distribution profiles were susceptible to anthropogenic activities, such as the leakage of septic tank wastewater. The dendrogram and heatmap revealed that three clusters of sample sites represented tributaries and the upstream areas, the downstream areas, and the potential pollutant source, and three clusters of antibiotics represented different concentration patterns. The high ecological risks of tetracycline, erythromycin and ciprofloxacin for algae and ofloxacin for plants were determined. These findings contributed to the establishment of a database for future monitoring and control of antibiotics in karst areas.

Comprehensive micropollutant screening using LC-HRMS/MS at three riverbank filtration sites to assess natural attenuation and potential implications for human health

Riverbank filtration (RBF) is used worldwide to produce high quality drinking water. With river water often contaminated by micropollutants (MPs) from various sources, this study addresses the occurrence and fate of such MPs at three different RBF sites with oxic alluvial sediments and short travel times to the drinking water well down to hours. A broad range of MPs with various physico-chemical properties were analysed with detection limits in the low ng L-1 range using solid phase extraction followed by liquid chromatography coupled to tandem high resolution mass spectrometry. Out of the 526 MPs targeted, a total of 123 different MPs were detected above the limit of quantification at the three different RBF sites. Of the 75-96 MPs detected in each river, 43-59% were attenuated during RBF. The remaining total concentrations of the MPs in the raw drinking water accounted to 0.6-1.6 μgL-1 with only a few compounds exceeding 0.1 μgL-1, an often used threshold value. The attenuation was most pronounced in the first meters of infiltration with a full elimination of 17 compounds at all three sites. However, a mixing with groundwater related to regional groundwater flow complicated the characterisation of natural attenuation potentials along the transects. Additional non-target screening at one site revealed similar trends for further non-target components. Overall, a risk assessment of the target and estimated non-target compound concentrations finally indicated during the sampling period no health risk of the drinking water according to current guidelines. Our results demonstrate that monitoring of contamination sources within a catchment and the affected water quality remains important in such vulnerable systems with partially short residence times.

Prevalent fecal contamination in drinking water resources and potential health risks in Swat, Pakistan

Fecal bacteria contaminate water resources and result in associated waterborne diseases. This study assessed drinking water quality and evaluated their potential health risks in Swat, Pakistan. Ground and surface drinking water were randomly collected from upstream to downstream in the River Swat watershed and analyzed for fecal contamination using fecal indicator bacteria (Escherichia coli) and physiochemical parameters (potential of hydrogen, turbidity, temperature, electrical conductivity, total dissolved solid, color, odor and taste). The physiochemical parameters were within their safe limits except in a few locations, whereas, the fecal contaminations in drinking water resources exceeded the drinking water quality standards of Pakistan Environmental Protection Agency (Pak-EPA), 2008 and World Health Organization (WHO), 2011. Multivariate and univariate analyses revealed that downstream urbanization trend, minimum distance between water sources and pit latrines/sewerage systems, raw sewage deep well injection and amplified urban, pastures and agricultural runoffs having human and animal excreta were the possible sources of contamination. The questionnaire survey revealed that majority of the local people using 10-20years old drinking water supply schemes at the rate of 73% well supply, 13% hand pump supply, 11% spring supply and 3% river/streams supply, which spreads high prevalence of water borne diseases including hepatitis, intestinal infections and diarrhea, dysentery, cholera, typhoid fever, jaundice and skin diseases in children followed by older and younger adults.

Modeling solute reactivity in a phreatic solution conduit penetrating a karst aquifer

A two-dimensional model for solute migration, transformation, and deposition in a phreatic solution conduit penetrating a karst aquifer is presented in which the solute is anthropogenic to the natural system. Transformation of a reacting solute in a solution conduit has generally been accepted as likely occurring but actual physical measurements and mathematical analyses of the suspected process have been generally minimally investigated, primarily because of the logistical difficulties and complexities associated with solute transport through solution conduits. The model demonstrates how a reacting solute might decay or be transformed to a product solute some of which then migrates via radial dispersion to the conduit wall where it may become adsorbed. Model effects vary for laminar flow and turbulent flow in the axial direction. Dispersion in the radial direction also exhibits marked differences for both laminar flow and turbulent flow. Reaction zones may enhance subsequent reactions due to some overlap resulting from the longitudinal dispersion caused by flow in the axial direction. Simulations showed that varying the reaction rate coefficient strongly affects solute reactions, but that varying deposition coefficients had only minimal impacts. The model was applied to a well-known tracer test that used the tracer dye, Rhodamine WT, which readily converts to deaminoalkylated Rhodamine WT after release, to illustrate how the model may be used to suggest one possible cause, in addition to other possible causes, for less than 100 tracer-mass recovery. In terms of pollutants in a karst aquifer the model also suggests one possible mechanism for pollutant transformation in a solution conduit.

Assessment of the origin and transport of four selected emerging micropollutants sucralose, Acesulfame-K, gemfibrozil, and iohexol in a karst spring during a multi-event spring response

The assessment of vulnerability in karst systems reveals to be extremely challenging since it varies significantly with time and highly depends on the identification of diffuse and concentrated infiltration from surface karst features. The origin, consumed loads, and transport mode of selected micropollutants (MPs) including two artificial sweeteners (ASWs) Sucralose (SUC) and Acesulfame-K (ACE-K), in addition to other less investigated pharmaceuticals such as the lipid regulator Gemfibrozil (GEM), and the contrast media Iohexol (IOX) were investigated in a karst system under dynamic conditions. A detailed analysis of selected spring responses' chemograph and hydrograph following a multi precipitation event shows that three of the tracked MPs, especially ACE-K, and to the exception of IOX, can be used as specific indicators for point source domestic wastewater in karst systems. They have revealed to be persistent, source specific, conservative, and highly correlated with in-situ parameters easily measurable at the spring (chloride and turbidity). Even if the selected MPs are found in the system during low flow periods, they are mostly transported to the spring through fast flow pathways from flushed wastewater with surface water or flood rainwater. The highest mass inflow of ACE-K, IOX and GEM originated from a sinking stream, while SUC infiltrated exclusively through fast infiltration points (dolines). Their breakthrough curves coincide with the arrival of new waters and turbidity peaks. Unlike IOX, the mass fluxes of ASWs, and GEM to a lesser extent, can be linearly correlated with chloride mass fluxes and turbidity flux. Moreover, the variance of the normalized breakthrough curves of the MPs with respect to a mean transit time, increases in that order IOX<GEM<Turbidity<SUC<ACE-K indicating a higher restitution time for ACE-K with respect to other spring signals.

Spatiotemporal scales of river-groundwater interaction - The role of local interaction processes and regional groundwater regimes

Drinking water production in the vicinity of rivers not only requires the consideration of different spatiotemporal scales and settings of river-groundwater interaction processes, but also of local and regional scale groundwater regimes. Selected case studies in combination with field-experiments and the setup of high-resolution groundwater flow models enabled the investigation of the spatiotemporal development of microbial (classical fecal indicator bacteria and total cell counts) and selected organic micropollutants in riverine and regional groundwater for different hydrological settings, including low and high flow conditions. Proxy indicators suitable as surrogates for the diverse contaminations in alluvial aquifers with different settings could be identified. Based on the study results, the basic elements for both groundwater management and river restoration concepts are derived, which include the: (1) compilation and evaluation of the "current state" concerning hydrogeology, microbiology and contamination by organic micropollutants, (2) definition of field-experiments to qualitatively assess variability related to the "current state", and (3) quantitative assessment of groundwater regimes, including variability of groundwater components and inflow areas, by application of high-resolution groundwater flow models. The validity and transferability of the concept and inferred controls (specifically drivers and controls of river-groundwater interaction) are tested by evaluations derived from hydraulic relationships to river sections with comparable settings and regional groundwater flow regimes in general. The results of our investigations illustrate the influence of dynamic hydrologic boundary conditions on river-groundwater interaction and of regional scale groundwater flow regimes on the water composition of riverine groundwater systems. It is demonstrated how to identify river sections and their variations with intensified river-groundwater exchange processes and how to quantify the transient character of the different groundwater components that constitute the raw water quality of drinking water wells near rivers.

Use of Molecular Markers to Compare Escherichia coli Transport with Traditional Groundwater Tracers in Epikarst

Bacterial contamination of karst aquifers is a global concern as water quality deteriorates in the face of decreasing water security. Traditional abiotic groundwater tracers, which do not exhibit surface properties similar to bacteria, may not be good proxies for risk assessment of bacterial transport in karst environments. This study examined the transport and attenuation of two isolates of in relation to traditional groundwater tracers (rhodamine WT dye and 1-μm-diam. latex microspheres) through ∼30 m of epikarst in western Kentucky. Differential movement of the four tracers was observed, with tracer behavior dependent on flow conditions. Dye arrived at the sampling site prior to particulates. Molecular biology techniques successfully detected bacteria in the cave and showed attenuation was greater for a bacterial isolate with high attachment efficiency compared with an isolate known to have low attachment efficiency. Microspheres were first detected simultaneously with the low-attachment isolate but attained maximum concentrations during increases in discharge >11 d post-injection. Bacteria were remobilized by storm events >60 d after injection, illustrating the storage capacity of epikarst with regard to potential contaminants. The two bacterial strains were not transported at the same rate within the epikarst, showing breakthroughs during differing storm events and illustrating the importance of cell surface chemistry in the prediction of microorganism movement. Moreover, this study has shown that molecular analysis can be successfully used to target, quantify, and track introduced microbial tracers in karst terrains.

Characterization of a managed aquifer recharge system using multiple tracers

Knowledge about the residence times of artificially infiltrated water into an aquifer and the resulting flow paths is essential to developing groundwater-management schemes. To obtain this knowledge, a variety of tracers can be used to study residence times and gain information about subsurface processes. Although a variety of tracers exists, their interpretation can differ considerably due to subsurface heterogeneity, underlying assumptions, and sampling and analysis limitations. The current study systematically assesses information gained from seven different tracers during a pumping experiment at a site where drinking water is extracted from an aquifer close to contaminated areas and where groundwater is artificially recharged by infiltrating surface water. We demonstrate that the groundwater residence times estimated using dye and heat tracers are comparable when the thermal retardation for the heat tracer is considered. Furthermore, major ions, acesulfame, and stable isotopes (δ²H and δ¹⁸O) show that mixing of infiltrated water and groundwater coming from the regional flow path occurred and a vertical stratification of the flow system exist. Based on the concentration patterns of dissolved gases (He, Ar, Kr, N₂, and O₂) and chlorinated solvents (e.g., tetrachloroethene), three temporal phases are observed in the ratio between infiltrated water and regional groundwater during the pumping experiment. Variability in this ratio is significantly related to changes in the pumping and infiltration rates. During constant pumping rates, more infiltrated water was extracted, which led to a higher dilution of the regional groundwater. An infiltration interruption caused however, the ratio to change and more regional groundwater is extracted, which led to an increase in all concentrations. The obtained results are discussed for each tracer considered and its strengths and limitations are illustrated. Overall, it is demonstrated that aquifer heterogeneity and various subsurface processes necessitate application of multiple tracers to quantify uncertainty when identifying flow processes.

Estimating the spatial distribution of artificial groundwater recharge using multiple tracers

Stable isotopes of water, organic micropollutants and hydrochemistry data are powerful tools for identifying different water types in areas where knowledge of the spatial distribution of different groundwater is critical for water resource management. An important question is how the assessments change if only one or a subset of these tracers is used. In this study, we estimate spatial artificial infiltration along an infiltration system with stage-discharge relationships and classify different water types based on the mentioned hydrochemistry data for a drinking water production area in Switzerland. Managed aquifer recharge via surface water that feeds into the aquifer creates a hydraulic barrier between contaminated groundwater and drinking water wells. We systematically compare the information from the aforementioned tracers and illustrate differences in distribution and mixing ratios. Despite uncertainties in the mixing ratios, we found that the overall spatial distribution of artificial infiltration is very similar for all the tracers. The highest infiltration occurred in the eastern part of the infiltration system, whereas infiltration in the western part was the lowest. More balanced infiltration within the infiltration system could cause the elevated groundwater mound to be distributed more evenly, preventing the natural inflow of contaminated groundwater. Dedicated to Professor Peter Fritz on the occasion of his 80th birthday.

Temporal variability of micro-organic contaminants in lowland chalk catchments: New insights into contaminant sources and hydrological processes

This paper explores the temporal variation of a broad suite of micro organic (MO) compounds within hydrologically linked compartments of a lowland Chalk catchment, the most important drinking water aquifer in the UK. It presents an assessment of results from relatively high frequency monitoring at a well-characterised site, including the type and concentrations of compounds detected and how they change under different hydrological conditions including exceptionally high groundwater levels and river flow conditions during 2014 and subsequent recovery. This study shows for the first time that within the Chalk groundwater there can be a greater diversity of the MOs compared to surface waters. Within the Chalk 26 different compounds were detected over the duration of the study compared to 17 in the surface water. Plasticisers (0.06-39μg/L) were found to dominate in the Chalk groundwater on 5 visits (38.4%) accounting for 14.5% of detections but contributing highest concentrations whilst other compounds dominated in the surface water. Trichloroethene and atrazine were among the most frequently detected compounds. The limit for the total pesticide concentration detected did not exceed EU/UK prescribed concentration values for drinking water. Emerging organic compounds such as caffeine, which currently do not have water quality limits, were also detected. The low numbers of compounds found within the hyporheic zone highlight the role of this transient interface in the attenuation and breakdown of the MOs, and provision of an important ecosystem service.

Transport and Attenuation of Particles of Different Density and Surface Charge: A Karst Aquifer Field Study

Although karst aquifers are far more susceptible to contamination than porous aquifers, with the transport of particulate matter being an important factor, little is known about the attenuation of solutes within karst aquifers and even less about the attenuation of particulate matter. These in situ investigations have therefore aimed to systematically identify the processes that influence the transport and attenuation of particles within a karst aquifer through multitracer testing, using four different types of 1 μm fluorescent particles and the fluorescent dye uranine. Each of the types of particles used were detected at the observed spring, which drains the investigated aquifer. However, the transport behavior varied significantly between the various particles and the uranine dye, with the breakthrough of particles occurring slightly earlier than that of uranine. Attenuation was determined from the tracer recovery and attributed to filtration processes. These processes were affected by the hydrophobicity and surface charge of the particles. Carboxylated polystyrene particles with a density and surface charge comparable to pathogenic microorganisms were found to be mobile in groundwater over a distance of about 3 km. No attenuation was observed for plain silica particles. Particles with these characteristics thus pose a major threat to karst spring water as they might occur as contaminants themselves or facilitate the transport of other contaminants.

Compound-Specific Stable Isotope Fractionation of Pesticides and Pharmaceuticals in a Mesoscale Aquifer Model

Compound-specific isotope analysis (CSIA) receives increasing interest for its ability to detect natural degradation of pesticides and pharmaceuticals. Despite recent laboratory studies, CSIA investigations of such micropollutants in the environment are still rare. To explore the certainty of information obtainable by CSIA in a near-environmental setting, a pulse of the pesticide bentazone, the pesticide metabolite 2,6-dichlorobenzamide (BAM), and the pharmaceuticals diclofenac and ibuprofen was released into a mesoscale aquifer with quasi-two-dimensional flow. Concentration breakthrough curves (BTC) of BAM and ibuprofen demonstrated neither degradation nor sorption. Bentazone was transformed but did not sorb significantly, whereas diclofenac showed both degradation and sorption. Carbon and nitrogen CSIA could be accomplished in similar concentrations as for "traditional" priority pollutants (low μg/L range), however, at the cost of uncertainties (0.4-0.5‰ (carbon), 1‰ (nitrogen)). Nonetheless, invariant carbon and nitrogen isotope values confirmed that BAM was neither degraded nor sorbed, while significant enrichment of (13)C and in particular (15)N corroborated transformation of diclofenac and bentazone. Retardation of diclofenac was reflected in additional (15)N sorption isotope effects, whereas isotope fractionation of transverse dispersion could not be identified. These results provide a benchmark on the performance of CSIA to monitor the reactivity of micropollutants in aquifers and may guide future efforts to accomplish CSIA at even lower concentrations (ng/L range).

Evaluation of polar organic micropollutants as indicators for wastewater-related coastal water quality impairment

Results from coastal water pollution monitoring (Lesvos Island, Greece) are presented. In total, 53 samples were analyzed for 58 polar organic micropollutants such as selected herbicides, biocides, corrosion inhibitors, stimulants, artificial sweeteners, and pharmaceuticals. Main focus is the application of a proposed wastewater indicator quartet (acesulfame, caffeine, valsartan, and valsartan acid) to detect point sources and contamination hot-spots with untreated and treated wastewater. The derived conclusions are compared with the state of knowledge regarding local land use and infrastructure. The artificial sweetener acesulfame and the stimulant caffeine were used as indicators for treated and untreated wastewater, respectively. In case of a contamination with untreated wastewater the concentration ratio of the antihypertensive valsartan and its transformation product valsartan acid was used to further refine the estimation of the residence time of the contamination. The median/maximum concentrations of acesulfame and caffeine were 5.3/178 ng L(-1) and 6.1/522 ng L(-1), respectively. Their detection frequency was 100%. Highest concentrations were detected within the urban area of the capital of the island (Mytilene). The indicator quartet in the gulfs of Gera and Kalloni (two semi-enclosed embayments on the island) demonstrated different concentration patterns. A comparatively higher proportion of untreated wastewater was detected in the gulf of Gera, which is in agreement with data on the wastewater infrastructure. The indicator quality of the micropollutants to detect wastewater was compared with electrical conductivity (EC) data. Due to their anthropogenic nature and low detection limits, the micropollutants are superior to EC regarding both sensitivity and selectivity. The concentrations of atrazine, diuron, and isoproturon did not exceed the annual average of their environmental quality standards (EQS) defined by the European Commission. At two sampling locations irgarol 1051 exceeded its annual average EQS value but not the maximum allowable concentration of 16 ng L(-1).

Use of two artificial sweeteners, cyclamate and acesulfame, to identify and quantify wastewater contributions in a karst spring

The identification and differentiation of different sources of contamination are crucial aspects of risk assessment in water resource protection. This is especially challenging in karst environments due to their highly heterogeneous flow fields. We have investigated the use of two artificial sweeteners, cyclamate and acesulfame, as an indicator set for contamination by wastewater within the rural catchment of a karst spring. The catchment was investigated in detail to identify the sources of artificial sweeteners and quantify their impact. Spring water was analysed following two different but typical recharge events: (1) a rain-on-snow event in winter, when no wastewater overflow from the sewer system was observed, and (2) an intense rainfall event in summer triggering an overflow from a stormwater detention basin. Acesulfame, which is known to be persistent, was quantified in all spring water samples. Its concentrations decreased after the winter event with no associated wastewater spillage but increased during the summer event following a recent input of untreated wastewater. Cyclamate, which is known to be degradable, was only detected following the wastewater inflow incident. The cyclamate signal matched very well the breakthrough of faecal indicator bacteria, indicating a common origin. Knowing the input function, cyclamate was used quantitatively as a tracer in transport modelling and the impact of 'combined sewer overflow' on spring water quality was quantified. Signals from artificial sweeteners were compared to those from bulk parameters (discharge, electrical conductivity and turbidity) and also to those from the herbicides atrazine and isoproturon, which indicate 'old' and 'fresh' flow components, respectively, both originating from croplands. High concentration levels of the artificial sweeteners in untreated wastewater (cyclamate and acesulfame) and in treated wastewater (acesulfame only) make them powerful indicators, especially in rural settings where wastewater input is relatively low, and in karst systems where dilution is often high.

Fecal pollution source tracking toolbox for identification, evaluation and characterization of fecal contamination in receiving urban surface waters and groundwater

The quality of surface waters/groundwater of a geographical region can be affected by anthropogenic activities, land use patterns and fecal pollution sources from humans and animals. Therefore, the development of an efficient fecal pollution source tracking toolbox for identifying the origin of the fecal pollution sources in surface waters/groundwater is especially helpful for improving management efforts and remediation actions of water resources in a more cost-effective and efficient manner. This review summarizes the updated knowledge on the use of fecal pollution source tracking markers for detecting, evaluating and characterizing fecal pollution sources in receiving surface waters and groundwater. The suitability of using chemical markers (i.e. fecal sterols, fluorescent whitening agents, pharmaceuticals and personal care products, and artificial sweeteners) and/or microbial markers (e.g. F+RNA coliphages, enteric viruses, and host-specific anaerobic bacterial 16S rDNA genetic markers) for tracking fecal pollution sources in receiving water bodies is discussed. In addition, this review also provides a comprehensive approach, which is based on the detection ratios (DR), detection frequencies (DF), and fate of potential microbial and chemical markers. DR and DF are considered as the key criteria for selecting appropriate markers for identifying and evaluating the impacts of fecal contamination in surface waters/groundwater.

Relationship between organic micropollutants and hydro-sedimentary processes at a karst spring in south-west Germany

Karst aquifers are known to be highly vulnerable to contamination due to their particular hydraulic characteristics. A number of parameters (such as turbidity, dissolved organic matter concentration, particle size distribution) have been proposed as proxies that can be used to detect changes in water quality or contamination of karst springs. However, most of these are not very specific concerning the source of any contamination. Organic micropollutants (OMPs) such as artificial sweeteners or herbicides are possible source-specific indicators that can be used in karst catchment areas, but real time monitoring is not as yet possible for these compounds. We have investigated the possibility of combining the source-specific features of OMPs with real-time measurements of electrical conductivity (EC) and turbidity by means of ECturbidity hysteresis plots. These plots allow for identifying different hydro-sedimentary processes. Our investigations were carried out at the Gallusquelle karst spring in south-west Germany, during high flow conditions that occurred in 2013 after heavy precipitation. The herbicide atrazine, which derives from the aquifer matrix, was detectable in the spring water until resuspended particles appeared at the spring. The herbicide metazachlor, which is present in recharge from cropland, was found to be associated with periods of direct transfer of particles originating from the land surface. The artificial sweetener cyclamate was used as a wastewater indicator, but neither hysteresis plots of EC and turbidity nor any other real-time parameters were able to detect the presence of cyclamate following a wastewater spill. Since EC and turbidity are easily measurable parameters, the systematic relationships of ECturbidity hysteresis behavior to OMPs might assist in the sustainable management of raw water within karst catchments.

A framework for assessing the retardation of organic molecules in groundwater: Implications of the species distribution for the sorption-influenced transport

The pH-dependent molecule speciation (charge state) in solution strongly influences the transport of ionizable organic compounds in the aquatic environment. Therefore, the sorption behavior is complex and reliable predictions only based on physico-chemical sorbate, sorbent and solution properties are challenging. A short overview of underlying sorption processes causing retardation during the solute transport in aquifers is completed by a description of approaches for estimating respective sorption coefficients/retardation factors and discussed together with their limitations. Based on these initial considerations, a systematic framework is proposed, which allows the assessment of transport properties of organic molecule species by their chemical nature (neutral, acidic, basic, ampholytic). As a result, the transport properties of many (ionizable) organic molecules of interest can be assessed and even first presumptions for the sorption behavior of new and not yet investigated molecules can be derived.