Tobias Geyer

Caffeine as an indicator for the quantification of untreated wastewater in karst systems.

Contamination from untreated wastewater leakage and related bacterial contamination poses a threat to drinking water quality. However, a quantification of the magnitude of leakage is difficult. The objective of this work is to provide a highly sensitive methodology for the estimation of the mass of untreated wastewater entering karst aquifers with rapid recharge. For this purpose a balance approach is adapted. It is based on the mass flow of caffeine in spring water, the load of caffeine in untreated wastewater and the daily water consumption per person in a spring catchment area. Caffeine is a source-specific indicator for wastewater, consumed and discharged in quantities allowing detection in a karst spring. The methodology was applied to estimate the amount of leaking and infiltrating wastewater to a well investigated karst aquifer on a daily basis. The calculated mean volume of untreated wastewater entering the aquifer was found to be 2.2 ± 0.5 m(3) d(-1) (undiluted wastewater). It corresponds to approximately 0.4% of the total amount of wastewater within the spring catchment.

Occurrence and spatial distribution of organic micro-pollutants in a complex hydrogeological karst system during low flow and high flow periods, results of a two-year study

Fifty-four different organic micro-pollutants (OMPs) including pharmaceuticals, pesticides, corrosion inhibitors and other typical wastewater compounds such as caffeine are repeatedly analyzed in approximately fifty groundwater observation points in a complex faulted and fractured carbonate aquifer system consisting of three spring catchment areas. With the applied HPLC-MS/MS method, achieving method quantification limits (MQL) of 1.2-28 ng L(-1), forty-four of the OMPs are detected in groundwater. Regarding the vertical distribution in the aquifer system the highest variety of OMPs occurs in the shallow aquifer. Most frequently detected compounds are atrazine together with the metabolites of several triazines, desethylatrazine (DEA) and desisopropylatrazine (DIA), the corrosion inhibitors 1H-benzotriazole and tolytriazoles and as pharmaceutical residues the anti-epileptic drug carbamazepine as well as the analgesic drug phenazone. Median OMP concentrations are in the range of 20-40 ng L(-1) with occasionally and locally higher concentrations of up to 6000 ng L(-1). Defined combinations of OMPs occur repeatedly in the same observation wells and allow to distinguish different input functions. The comparison of detection frequency with the number of prescribed doses gives information about the specific persistence of pharmaceuticals. The analgesic phenazone exhibits a peculiar high detection frequency, although it is recently not prescribed in significant amounts. The detection of the estrogen antagonist tamoxifen (6-17 ng L(-1)) in a groundwater flow system is reported for the first time.

Identification of the attenuation potential of a karst aquifer by an artificial dualtracer experiment with caffeine.

Little is known with respect to the attenuation capacity of karst aquifers. Even less is known about the risk posed by emerging micropollutants in these systems. In order to identify the attenuation potential of karst aquifers in-situ and to estimate the risk posed by micropollutants, a dualtracer test was conducted in this study in order to investigate differential transport in the subsurface: The reactive compound caffeine was used as a tracer to indicate the attenuation capacity within the aquifer in-situ. Due to the low limit of quantification, only small amounts of caffeine needed to be injected. To calibrate a model and to visualize the attenuation of caffeine a conservative reference tracer (uranine) is injected simultaneously. The methodology is tested in a well-characterised karst system in southwest Germany. The results indicate a significantly higher attenuation rate than was expected for karst aquifers. The attenuation is decribed as a first-order process. The corresponding half-life is 104 h. This low half-life suggests that a generally assumed low natural attenuation capacity of karst aquifers is unjustified. The observed mass loss of caffeine illustrates the potential of caffeine to be used as reactive tracer for indicating in-situ attenuation capacity within highly hydraulically conductive systems, such as karst aquifers. Due to the high attenuation rate of caffeine it does not pose a threat as a long-time contaminant. In combination with a conservative reference tracer an economical and environmentally benign method is presented in this manuscript for the in-situ determination of the attenuation capacity of highly conductive aquifer systems.

Investigating the dynamics of two herbicides at a karst spring in Germany: Consequences for sustainable raw water management.

While karst aquifers are considered as rapid flow and transport systems, their high potential for long-term storage is often ignored. However, to achieve a sustainable raw water quality for drinking water production, the understanding of this potential is highly essential. In this study, the transport dynamics of the two herbicides metazachlor and atrazine as well as a degradation product of the latter (desethylatrazine) were investigated at a karst spring over 1 year. Even 20 years after its ban in Germany, atrazine and its degradation product were almost always detectable in the spring water in the low ng L(-1) range (up to 5.2ng L(-1)). Metazachlor could only be detected after precipitation events, and the observed concentrations (up to 82.9ng L(-1)) are significantly higher than atrazine or desethylatrazine. Comparing the dynamics of the herbicides with the inorganic ions Ca(2+), Mg(2+) and electrical conductivity, a positive correlation of atrazine with these parameters could be observed. From this observation, atrazine is concluded to be located within the aquifer matrix. To achieve a sustainable raw water management at karst springs, the rapidness of these systems needs to be highlighted as well as their long-term storage potential. Persistent substances or transformation products are prone to deteriorate the raw water quality for decades.

Differentiated characterization of karst aquifers: some contributions

Because of the small radius of investigation of hydrogeological standard testing methods, the characterization of karst aquifers is still a challenge. The development of a karst conduit system introduces an element of large contrast in hydraulic conductivity in the hydraulic parameter field of a karst aquifer. It leads to complex flow patterns and transport phenomena that differ significantly from those observed in porous and fissured media. While on a local, i.e., borehole scale, the fissured matrix of karst aquifers can be regarded as a continuum, on a regional, i.e., catchment scale, the drainage of the aquifer system is controlled by the conduit system, which may have a highly anisotropic geometry. Therefore, characterization of karst aquifers requires a differentiated approach by the combination of various hydrogeological field methods or the application of large-scale tests, which cover the scale of dominant aquifer heterogeneities. Existing numerical modeling approaches can be applied for integral data interpretation on catchment scale.

Evaluation and application of organic micro-pollutants (OMPs) as indicators in karst system characterization.

This study presents chances and challenges associated with the application of organic micro-pollutants (OMPs) as indicators in karst system characterization. The methodology and options of possible indications were evaluated based on the interpretation of the spatial distribution of 54 compounds in groundwater in combination with a complex geological setting consisting of multiple aquifer horizons and tectonic faults. A high variety of OMPs are released mainly in an urban area leading to concentrations of several nanograms per liter up to micrograms per liter, which are detectable using a high-performance liquid chromatography with subsequent tandem mass spectrometry (HPLC-MS/MS) method. Since characteristic patterns of spatial distribution were repeatedly observed during a 2-year observation period, important criteria of the aforementioned indicator application are fulfilled. Triazoles, compounds with recent high emission rates, could be successfully applied for the identification of flow directions and the delineation of catchment areas. Concentrations and the number of OMPs are believed to be dependent on properties of covering rock layers. Therefore, OMPs can also be used as a validation tool for vulnerability mapping. Compounds, such as triazines, persistent in the system for more than two decades, demonstrate the interaction between different parts of the aquifer system and the hydraulic characteristics of a tectonic fault zone. Such indicator potentials complement those of artificial tracer tests. Point sources of OMPs and their impact on groundwater could be identified qualitatively. In combination with the interpretation of the geological setting, the distribution of OMPs provides essential information for the development of a conceptual hydrogeological model.

Turbulent and Laminar Flow in Karst Conduits Under Unsteady Flow Conditions: Interpretation of Pumping Tests by Discrete Conduit-Continuum Modeling

Due to the duality in terms of (1) the groundwater flow field and (2) the discharge conditions, flow patterns of karst aquifer systems are complex. Estimated aquifer parameters may differ by several orders of magnitude from local (borehole) to regional (catchment) scale because of the large contrast in hydraulic parameters between matrix and conduit, their heterogeneity and anisotropy. One approach to deal with the scale effect problem in the estimation of hydraulic parameters of karst aquifers is the application of large-scale experiments such as long-term high-abstraction conduit pumping tests, stimulating measurable groundwater drawdown in both, the karst conduit system as well as the fractured matrix. The numerical discrete conduit-continuum modeling approach MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is employed to simulate laminar and nonlaminar conduit flow, induced by large-scale experiments, in combination with Darcian matrix flow. Effects of large-scale experiments were simulated for idealized settings. Subsequently, diagnostic plots and analyses of different fluxes are applied to interpret differences in the simulated conduit drawdown and general flow patterns. The main focus is set on the question to which extent different conduit flow regimes will affect the drawdown in conduit and matrix depending on the hydraulic properties of the conduit system, i.e., conduit diameter and relative roughness. In this context, CFPM1 is applied to investigate the importance of considering turbulent conditions for the simulation of karst conduit flow. This work quantifies the relative error that results from assuming laminar conduit flow for the interpretation of a synthetic large-scale pumping test in karst.

Effect of Unsaturated Flow Modes on Partitioning Dynamics of Gravity‐Driven Flow at a Simple Fracture Intersection: Laboratory Study and Three‐Dimensional Smoothed Particle Hydrodynamics Simulations

In this work, we study gravity-driven flow of water in the presence of air on a synthetic surface intersected by a horizontal fracture and investigate the importance of droplet and rivulet flow modes on the partitioning behavior at the fracture intersection. We present laboratory experiments, three-dimensional smoothed particle hydrodynamics (SPH) simulations using a heavily parallelized code, and a theoretical analysis. The flow-rate-dependent mode switching from droplets to rivulets is observed in experiments and reproduced by the SPH model, and the transition ranges agree in SPH simulations and laboratory experiments. We show that flow modes heavily influence the “bypass” behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), the flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency increases. For rivulet flows, the initial filling of the horizontal fracture is described by classical plug flow. Meanwhile, for droplet flows, a size-dependent partitioning behavior is observed, and the filling of the fracture takes longer. For the case of rivulet flow, we provide an analytical solution that demonstrates the existence of classical Washburn flow within the horizontal fracture.

Herausforderungen bei der Charakterisierung von Karstgrundwasserleitern

rung numerischer Modelle liefern. In den aktuellen Themenheften sind dazu verschiedene Beispiele dokumentiert. Zudem konnen neue Methoden im Bereich der Messtechnik und Analytik einen wichtigen Beitrag zur Charakterisierung der Systeme liefern. Die Anwendung von Datenloggern erlaubt z. B. die zeitlich hochaufgeloste Erfassung der Dynamik von Karstquellen als Resultat schneller Stromungsund Transportprozesse. Fur die Untersuchung der langsamen mobilen Flieskomponente wurde in der Vergangenheit haufig Tritium verwendet, dessen heutige Anwendung jedoch stark erschwert ist. Die Anwendung und Vergleichbarkeit alternativer Umwelttracer (z. B. Gastracer) in der Karsthydrogeologie ist deshalb zu prufen. Verschiedene aktuelle Studien zeigen zudem, dass andere Indikatoren im Quellwasser, wie z. B. organische Spurenstoffe und Partikel, einen wichtigen Beitrag fur die Bestimmung der Herkunft und Verweilzeit des Wassers leisten konnen. Die Verweilzeitenverteilung im Fliessystem wird neben der Interaktion von schnellen und langsamen Flieskomponenten auch von der zeitlichen und raumlichen Verteilung der Grundwasserneubildung gesteuert. Wahrend die Neubildungsmenge relativ genau und flachendeckend ermittelt werden kann, z. B. mit Bodenwasserhaushaltsmodellen, fehlen immer noch prozesstreue Ansatze zur Simulation der Wasserperkolation durch die ungesattigte Festgesteinszone. Die Charakterisierung und Modellierung von Karstgrundwasserleitern ist somit aufgrund ihrer komplexen Strukturund Prozessvielfalt immer noch eine grose Herausforderung und wird auch in Zukunft ein spannendes Feld der Hydrogeologie bleiben. Das vorliegende und das vorherige Themenheft prasentieren Beitrage zur Karsthydrogeologie aus dem deutschsprachigen Raum (D-A-CH). Es sind aber auch internationale Autoren und Studien vertreten. Die Themenhefte sind daher auch ein Beitrag zu den Aktivitaten der IAH Karstkommission (www.iah.org/karst). Die nachhaltige Bewirtschaftung von Karstwasserressourcen erfordert systembeschreibende Charakterisierungsansatze und Vorhersagewerkzeuge. Traditionelle hydrogeologische Gelandeuntersuchungen und Modelltechniken sind haufig auf porose Medien fokussiert und vernachlassigen stark anisotrope Strukturelemente, die neben nichtlinearen Stromungsregimes auch uber grose Skalenbereiche zu komplexen hydraulischen Parameterfeldern fuhren. Die Parametrisierung numerischer Modelle in der Karsthydrogeologie erfordert deshalb eine differenzierte Herangehensweise. Wahrend die hydraulischen Kennwerte der geklufteten Matrix auf der lokalen Skala relativ einfach durch Bohrlochversuche bestimmt werden konnen, ist es fast unmoglich, reprasentative hydraulische Kennwerte durch kontrollierte Experimente auf der Einzugsgebietsskala zu ermitteln. Dies liegt darin begrundet, dass Karstrohren eine entscheidende Funktion fur die einzugsgebietsweite Entwasserung des Untergrundes besitzen, aufgrund ihres geringen Volumenanteils am Gesamtsystem jedoch nur selten durch Bohrungen erfasst werden. Markierungsversuche sind bewahrte Werkzeuge fur die Charakterisierung des hochdurchlassigen Rohrensystems. Untersuchungen von Quellschuttung und von anderen Quellparametern erlauben zusatzlich die integrale einzugsgebietsweite Untersuchung der Grundwasserdynamik und konnen deshalb wichtige Informationen fur die Kalibrie-

Charakterisierung zweier Karstsysteme mithilfe organischer Spurenstoffe

ZusammenfassungIn der vorliegenden Arbeit wird das Auftreten organischer Spurenstoffe in zwei hinsichtlich der geologischen Verhältnisse und der Flächennutzung unterschiedlichen Karstgebieten diskutiert.In einem urban geprägten, moderat verkarsteten Quelleinzugsgebiet mit einer hohen Anzahl lokaler Eintragsquellen (beispielsweise Altlasten, Kanalleckagen) ist gegenüber einem landwirtschaftlich dominierten Gebiet das Spektrum der gefundenen Stoffe breiter. Die Konzentrationen der meisten dieser Stoffe nehmen auf der Fließstrecke zu den Quellaustritten bis unter die Bestimmungsgrenzen ab und können daher nur über ein flächendeckendes Messstellennetz erfasst werden. In den Quellen finden sich vorwiegend Stoffe, die entweder durch eine weite rezente Anwendungsverbreitung oder hohe Persistenz charakterisiert sind.In der Quelle eines stärker verkarsteten und somit höher durchlässigen Grundwasserfließsystems werden zeitlich variierend auch biologisch leicht abbaubare Substanzen detektiert. Aufgrund hoher Fließgeschwindigkeiten erfordern Untersuchungen dieses Fließsystems ein zeitlich hochaufgelöstes Monitoring organischer Spurenstoffe.Somit haben neben den jeweiligen Stoffeigenschaften auch die hydrogeologischen Systemcharakteristika erheblichen Einfluss auf das Spektrum der nachweisbaren Stoffe.AbstractIn the presented work the occurrence of organic micro-pollutants is discussed for two karst areas with different geological characteristics and land-use patterns.Within an urban moderately karstified catchment with a large number of local input sources (e.g. contaminated sites, sewer leakages), a greater variety of micro-pollutants is found compared to a rural area. Mostly the concentrations of these compounds decrease below quantification limits before emerging at the spring and can therefore only be detected by a comprehensive network of sampling points. Springs show the presence of micro-pollutants, either recently applied in large amounts or characterized by high persistence.At the outlet of a highly karstified and consequently highly permeable aquifer readily biodegradable compounds are detected. Due to high groundwater flow velocities investigations of micro-pollutants require a highly resolved monitoring.Therefore, beside substance properties, also hydrogeological characteristics affect the spectrum of detectable micro-pollutants.