Conference Agenda

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Session Overview
9.2 Groundwater quality: new developments on understanding transport and mobility of contaminants related to anthropogenic impacts
Tuesday, 21/Sept/2021:
4:15pm - 5:45pm

Session Chair: Tobias Licha, Ruhr Universität Bochum
Session Chair: Ferry Schiperski, TU Berlin

Session Abstract

Groundwater quality is widely compromised by anthropogenic impact. This becomes evident by the presence of numerous anthropogenic organic and inorganic contaminants in groundwater. Contaminants are of widespread origin. They enter the groundwater associated to different processes such as sewer failure, agricultural activities or contaminated industrial sites.Understanding the input mechanism, transport, attenuation and degradation processes in short and long term is crucial for sustainable groundwater development.Although unwanted, contaminants even in smallest quantities might provide information for locating their input or allow for understanding transport and attenuation processes within aquifers. In addition, microbial communities might not only be harmful but assist in the degradation of harmful substances.We call for contributions that deal with groundwater quality in all type of aquifers (e.g. alluvial, fractured, and karst aquifers). We welcome topics such as urban groundwater, new tools for water quality characterization, organic micropollutants in groundwater, microbial contaminants (such as bacteria, virus, and protozoans), groundwater remediation, and water quality monitoring.

4:15pm - 4:45pm
Session Keynote

Threats to groundwater quality in the Anthropocene

Christian Moeck1, Mario Schirmer1,2

1Eawag, Department of Water Resources and Drinking Water, Swiss Federal Institute of Aquatic Science and Technology, Switzerland; 2University of Neuchâtel, Centre of Hydrogeology and Geothermics (CHYN), Switzerland

Groundwater quality degradation is a well-recognized phenomenon and has received considerable attention since the industrial revolution. In spite of this, many aspects concerning the understanding and management of groundwater as a resource remain complex, and adequate information, in many cases, remains elusive. Strategies to protect and manage groundwater quality are often based on limited data and thus restricted system knowledge.

As questions remain about the behaviour and prediction of well-known groundwater contaminants, new concerns around emerging contaminants are on the increase. In urban, industrial and agricultural areas especially, groundwater quality is widely compromised by anthropogenic impacts. Water management in such areas is recognized as a very complex task, in terms of different spatial and temporal scales, as well as understanding the input mechanism, transport and attenuation processes: crucial for sustainable groundwater management. The residence time of contaminants within groundwater bodies can be anywhere from weeks to decades, depending on physico-chemical properties of compound and environmental conditions. It is therefore well-accepted that subsurface heterogeneity necessitates the application of multiple tracers and methods to minimizing uncertainties and to uncovering subsurface processes that would not have been identified by the application of e.g. only one tracer. Thus, although contaminants are typically unwanted, they can provide crucial insights into flow and transport processes within aquifers.

This presentation highlights some of the key contaminants that originate from anthropogenic activities, reviews some of the major controls on groundwater contamination, and includes a case study that addresses historic and emerging issues in contaminant hydrogeology.

4:45pm - 5:00pm

Mutual effects of pH and ionic strength on the mobility of metoprolol in saturated quartz sand

Joshua Sawall, Ferry Schiperski

Technische Universität Berlin

Emerging micropollutants such as lifestyle drugs, pesticides, and pharmaceuticals are increasingly detected in the aquatic environment. To counter possible threats posed by these pollutants, their transport behaviour needs to be thoroughly understood.

In this study, 22 laboratory column transport experiments were conducted at selected pH and Na+ concentrations with natural quartz sand as sorbent to determine transport behaviour of the beta-blocker metoprolol (MTP, pKa=9.67) at various conditions. MTP breakthrough curves were measured at pH 3, 6, and 11, as well as NaCl concentrations of 1, 10, and 100 mM/l to account for coupled effects. The observed mean R ranges from R=1.04 (pH 11; 100 mM/l NaCl) to R=10.5 (pH 5.6; 1 mM/l NaCl).

An ion exchange equation was used to model CEC and exchange coefficients of Na+, H+ and MTP using a least square refinement routine considering the whole dataset of 43 retardation values.

With the model, a high R-regime at low cation concurrence (c(NaCl)~1 mM/l) and neutral pH (5<pH<9) could be identified. Decreasing of retardation can be attributed to: (1) increasing Na+ concurrence, (2) decreasing pH at pH<5 due to lowered zeta potential and i.e. negatively charged sites covered by H+, and (3) increasing pH at pH>8.5 as a result of changing MTP speciation.

5:00pm - 5:15pm

Investigating Nitrate Pollution Sources and NaturalBackground in Groundwater of the Densu Basin: A Model-based Approach

George Yamoah Afrifa1, Larry-pax Chegbeleh1, Patrick Asamoah Sakyi1, Mark Sandow Yidana1, Yvonne Sena Akosua Loh1, Theophilus Ansah-Narh2, Evans Manu3,4,5

1Department of Earth Science, University of Ghana; 2Ghana Space Science & Technology Institute (GSSTI), Ghana Atomic Energy Commission (GAEC); 3Institute of Geosciences, University of Potsdam, Potsdam Germany; 4CSIR-Water Research Institute, Accra Ghana; 5German Research Center for Geosciences, Telegrafenberg, 14473 Potsdam, Germany

Nitrate is one of the dominant chemical pollutants of groundwater, and there is a need to mitigate groundwater pollution in rural, urban and industrial terrains in an aquifer system. The study assesses the extent of nitrate pollution in the Densu Basin because of its predominance in agriculture and urbanized vicinities by employing robust techniques for estimating both the natural background and human-induced concentrations. The statistical methods used to estimate these concentrations are the pre-selection method, graphical approach (probability plot),non-parametric approach (kernel density estimation), and parametric approach (Gaussian mixture model). The study shows that the Gaussian mixture model is robust enough in determining the spectral distribution and clustering of the nitrate concentration in the basin. It estimated the natural background and human-induced concentration at1.7±1.3 and 9.8±5.6, respectively. The results show that the natural background concentration in the basin is more dominant and hence, conducive for drinking. Also, we show that26%of anthropogenic sources have leaked into the natural groundwater of the Basin. The data suggest that the nitrate concentration in the Densu aquifer system is sourced from agricultural input, domestic effluent and atmospheric deposition. High nitrate loading was observed in areas of active agricultural activities (Suhum, AkwapemNorth, Ayensuano and Upper West Akim). These areas should be protected from further anthropogenic exposure

5:15pm - 5:30pm

Inverse modelling of transport distance to reduce ambiguities of microbial and chemical source tracking in karst catchments

Johannes Zirlewagen1, Ferry Schiperski1, Tobias Licha2, Traugott Scheytt3

1Technische Universität Berlin, Germany; 2Ruhr-University Bochum, Germany; 3TU Bergakademie Freiberg, Germany

The identification of contamination sources is vital for water protection, especially in highly vulnerable karst aquifers. Contamination sources might be distinguished by host-specific DNA markers of bacteria (Microbial Source Tracking, MST) or source-specific indicator compounds (Chemical Source Tracking, CST). These methods can help to identify a type of contamination source but fail to distinguish similar contaminant signals from different origins, e.g. multiple points of wastewater infiltration. Transport modelling can reduce these ambiguities by considering the time course of contaminant concentration, thereby allowing for a better allocation of the input source. However, flow in karst aquifers is highly heterogeneous and very dynamic. Hence, distributed numerical transport models on catchment scale are complex, difficult to parameterise and suffer from manifold ambiguities.

Here, an approach is presented, which aims at improving identification of contamination sources by combining MST/CST with transport modelling. Fast (conduit) transport is represented by a 1-D problem and a maximum transport distance for contamination events is modelled. The model is based on (semi-)analytical solutions of transport models, well-established in tracer test analysis to estimate apparent tracer velocities. In this study, a-priori knowledge about velocities and input times is used to inversely model transport lengths from contaminant breakthrough curves.

The inverse transport model (implemented in GNU Octave) was validated and parameter sensitivities were analysed. The maximum transport distance approach was shown to perform well during periods of flow recession. It was applied successfully to a contamination event at a karst spring and allowed for assigning its input to a stormwater tank.

5:30pm - 5:45pm

Multi-paprameter monitoring at alpine karst springs to identify suitable early-warning indicators for bacterial contamination

Simon Frank, Nadine Goeppert, Nico Goldscheider

Karlsruhe Institute of Technology (KIT), Germany

In alpine regions, karst springs are important sources of drinking water but highly vulnerable to temporary contamination, particularly in response to rainfall events. This variability of water quality requires rapid determination methods of contamination parameters. In this study, we present a multi-parameter approach to determine the dynamics of fecal bacteria, organic carbon and particles at alpine karst springs.

Conventional cultivation-based analysis of fecal bacteria such as E. coli is time-consuming. The measurement of the enzymatic activity of E. coli could prove to be a valuable tool for water-quality monitoring in near real time. We used an automated device (ColiMinder) to measure β-D-glucoronidase (GLUC) at an alpine karst spring. To assess the relations between GLUC activity, discharge dynamics and contamination patterns, multiple hydrochemical, physicochemical and microbiological parameters were measured in high resolution. We observed strong correlations between small particles (1.0 and 2.0 µm), conventional E. coli results, ATP measurements and total organic carbon. These parameters also show strong and significant negative correlations with the electrical conductivity. At high contamination levels, GLUC activity also reveals good correlations with E. coli and small particles.

The results demonstrate that the investigated karst springs showed fast and marked responses of all investigated water-quality parameters to rain events. At high contamination levels, GLUC and particle-size distribution are suitable parameters for the rapid assessment of bacterial contamination in high resolution. While GLUC activity alone cannot substitute conventional determination methods, a combined use of these parameters is a promising approach for an early-warning system regarding bacterial contamination.