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The persistence of the artificial sweetener acesulfame potassium (ACE) in wastewater treatment and subsequently in the aquatic environment has made it a widely used marker of wastewater in both surface water and groundwater. However, the recently observed biodegradation of ACE during wastewater treatment has questioned the validity of this application. In this study, we assessed the use of ACE not only as a marker of wastewater, but also as a transient wastewater tracer that allows both the calculation of mixing ratios and travel times through the aquifer as well as the calibration of transient groundwater flow and mass transport models. Our analysis was based on the data obtained in a nearly 8-year river water and groundwater sampling campaign along a confirmed wastewater-receiving riverbank filtration site located close to a drinking water supply system. We confirm that temperature controls ACE concentrations and thus their seasonal oscillation. River water data showed that ACE loads decreased from 1,500-4,000 μg·s−1 from December to June (cold season; T<10°C) to 0-500 μg·s−1 from July to November (warm season; T>10°C). This seasonal oscillation was transferred to the aquifer and preserved >3 km through the aquifer, with ACE concentrations oscillating between values below the detection limit in the warm season to 0.15 μg·L−1 in the cold season. The seasonal variation in ACE degradation during wastewater treatment enables the sweetener’s use as a transient tracer of wastewater inflows and riverbank filtration. In addition, the arrival time of the ACE concentration peak can be used to estimate groundwater flow velocity and mixing ratios, thereby demonstrating its potential in the calibration of groundwater numerical models.

&lt;p&gt;Fluvio-glacial aquifers in subalpine quaternary basins are global sources of drinking water.&lt;br&gt;Water works need to consider the geological framework of such aquifers to optimize&amp;#160;&lt;br&gt;groundwater management. This can be achieved by developing 3D geological models, which&amp;#160;&lt;br&gt;act as powerful tools for aquifer visualization and estimation of hydraulic properties. In recent&amp;#160;&lt;br&gt;years 3D geological modeling has emerged as an asset to sustainable groundwater management.&amp;#160;&lt;br&gt;However, the implementation of such models is no trivial task and requires expert geological&amp;#160;&lt;br&gt;knowledge. In this study a 3D geological model is developed for a subalpine quaternary basin,&lt;br&gt;that provides drinking water to a major city. The relationship between aquifer geometry and&amp;#160;&lt;br&gt;heterogeneity, preferential flow paths, and observed hydraulic and hydrochemical trends is&lt;br&gt;investigated. A database consisting of around 300 bore logs as well as geophysical, hydraulic&lt;br&gt;and hydrochemical data provides the foundation for the 3D geological model. The software&amp;#160;&lt;br&gt;package Leapfrog Works is employed to create the model. The resulting model depicts the&amp;#160;&lt;br&gt;complexity of the fluvio-glacial stratigraphy and the hydrogeological units of the study area&amp;#160;&lt;br&gt;and demonstrates the retarding effect that glacial terraces can have on flood wave propagation&amp;#160;&lt;br&gt;in aquifers. It allows the assessment of total groundwater volume and areas of low hydraulic&amp;#160;&lt;br&gt;conductivity. Our understanding of aquifer interconnectivity and constraints imposed on&amp;#160;&lt;br&gt;groundwater flow in fluvio-glacial quaternary sediment basins is improved. As such,&amp;#160;&lt;br&gt;recommendations for future groundwater explorations in subalpine basins are provided.&lt;/p&gt;

&lt;p&gt;A sub-alpine catchment hosts a drinking water plant that collects groundwater through a series of drains. The catchment is crossed by a river that recharges the aquifer with potentially polluted water. The waterworks managers need a management strategy to maximize groundwater collection and minimize the probability to extract river water. This request was addressed by means of a groundwater model that simulates the mixing of river water and groundwater under a stochastic framework.&lt;/p&gt;&lt;p&gt;Samples of river water show the presence of Gadolinium, a rare earth element used as a contrast agent (GBCA) for magnetic resonance imaging. This element is also recurrently found in samples taken from some monitoring wells, and previous studies have determined its suitability as a tracer of solute dispersion. We used it as an indicator of partitioning between river water and original groundwater.&lt;/p&gt;&lt;p&gt;We built a simple, fast-running numerical groundwater model with the FEM code Feflow (DHI). We coupled it with PESTPP-IES, an optimization tool that implements the ensemble-smoother form of the Gauss-Levenberg-Marquardt algorithm. Through it, an ensemble of &quot;realistic&quot; parameter fields was generated, all of which support a good fit between model outputs and the calibration dataset. The latter included mixing ratios (calculated by measured Gadolinium concentrations) and groundwater levels. To simulate Gadolinium spread in groundwater, we used particle tracking instead of building an advective-dispersive transport model, because the latter is costlier to build and slower to run, therefore it does not allow the high number of runs required by PESTPP-IES. Although dispersion is not explicitly represented, its role is surrogated by uncertainty in hydraulic conductivity.&lt;/p&gt;&lt;p&gt;With this study, we built the engine of a decision support system that will optimize waterworks management. We also demonstrated that a lean, purpose-driven model is adequate in simulating solute transport in complex hydrogeological systems. Gadolinium concentrations were instrumental in identifying the partitioning between river water and groundwater.&lt;/p&gt;