Scientists and practitioners agree that integrated water resource management is necessary, with an increasing need for research at the regional scale (10 3 to 10 5 km 2 ). At this scale interactions between environmental and human systems are fully developed and global change is linked to local actions. The groundwater-surface water interaction (GW-SW) is of particular interest. Herein we review the scientific journal literature and examine GW-SW at the regional scale. We briefly review all existing literature on GW-SW, then summarise its characteristics at different scales and identify specific challenges of the regional scale. We explore whether GW-SW should be treated differently at regional and local scales. Regional GW-SW is rarely examined in experimental field studies, which almost exclusively cover small areas. However, GW-SW is often integral to large scale coupled models. Thus, we collate information about existing models and their regional applications. Fully coupled, physics-based models have great potential to meet the technical challenges. However, limited data availability hampers the application of complex models at the regional scale and loosely coupled schemes are more widely applied. Many integrated modelling concepts have been published, but none have been applied in a wide range of settings. Thus, it is impossible to compare the performance of different approaches. Comparative analyses of existing regional scale integrated models in the context of different data availability and geographic conditions are needed. Unfortunately, peer-reviewed journal literature no longer provides a representative picture of the subject as models are becoming Btoo big to be published^or too pragmatic.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are found in aquatic systems, flora, and fauna worldwide. These potentially harmful compounds are also frequently detected in Sweden and have already resulted in severe problems for public drinking water supply, i.e., some wells had to be closed due to high PFAS concentrations both in raw water and produced drinking water. Knowledge on PFAS occurrence in Sweden is still quite low, although monitoring is currently ongoing. This work describes potential sources for PFASs to enter the drinking water supply in Sweden and compares different occurrences of PFASs in raw and drinking water in the country. Moreover, the monitoring history, the legal situation, and remediation actions taken are presented. Finally, future challenges and the way forward in Sweden are discussed.

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Abstract. Although column experiments are frequently used to investigate the transport of organic micropollutants, little guidance is available on what they can be used for, how they should be set up, and how the experiments should be carried out. This review covers the use of column experiments to investigate the fate of organic micropollutants. Alternative setups are discussed together with their respective advantages and limitations. An overview is presented of published column experiments investigating the transport of organic micropollutants, and suggestions are offered on how to improve the comparability of future results from different experiments. The main purpose of column experiments is to investigate the transport and attenuation of a specific compound within a specific sediment or substrate. The transport of (organic) solutes in groundwater is influenced by the chemical and physical properties of the compounds, the solvent (i.e., the groundwater, including all solutes), and the substrate (the aquifer material). By adjusting these boundary conditions a multitude of different processes and related research questions can be investigated using a variety of experimental setups. Apart from the ability to effectively control the individual boundary conditions, the main advantage of column experiments compared to other experimental setups (such as those used in field experiments, or in batch microcosm experiments) is that conservative and reactive solute breakthrough curves can be derived, which represent the sum of the transport processes. There are well-established methods for analyzing these curves. The effects observed in column studies are often a result of dynamic, non-equilibrium processes. Time (or flow velocity) is an important factor, in contrast to batch experiments where all processes are observed until equilibrium is reached in the substrate-solution system. Slight variations in the boundary conditions of different experiments can have a marked influence on the transport and degradation of organic micropollutants. This is of critical importance when comparing general results from different column experiments investigating the transport behavior of a specific organic compound. Such variations unfortunately mean that the results from most column experiments are not transferable to other hydrogeochemical environments but are only valid for the specific experimental setup used. Column experiments are fast, flexible, and easy to manage; their boundary conditions can be controlled and they are cheap compared to extensive field experiments. They can provide good estimates of all relevant transport parameters. However, the obtained results will almost always be limited to the scale of the experiment and are not directly transferrable to field scales as too many parameters are exclusive to the column setup. The challenge for the future is to develop standardized column experiments on organic micropollutants in order to overcome these issues.

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