Solution Exercise 1

Each of the terms ‘groundwater system’, ‘aquifer’ and ‘aquifer system’ refers to a subsurface domain containing groundwater. ‘Groundwater system’ is a more generic term, while ‘aquifer’ and ‘aquifer system’ are more specific: they have a hydraulic connotation since they are defined based on contrasts in hydraulic properties in the subsurface. The term ‘groundwater system’ can be used to indicate an aquifer or aquifer system, but it may also refer to conceptual groundwater models, such as a linear reservoir or other black-box models that simulate groundwater outflow to streams; groundwater flow systems as defined by Tóth; or groundwater bodies such as basic groundwater management units adopted under the European Union Water Framework Directive. In cases where aquifers are used to store carbon dioxide or substances other than water, the term ‘groundwater system’ is less appropriate.

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Solution Exercise 2

The reply to this question is specific to the individual reader and the country in which he or she resides.

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Solution Exercise 3

The flow pattern is defined by the flow paths between the zones of groundwater inflow (recharge zones) and groundwater outflow (discharge zones). Groundwater age is minimal in the recharge zones and steadily increases along the flow paths in the down-flow direction. The slower the groundwater flow rate, the higher the groundwater age along the flow path as groundwater approaches the discharge zones. Groundwater passing through deeper parts of the flow domain follows longer flow paths between recharge and discharge zones and the flow velocities are lower; in some cases, the flow even stagnates. Therefore, groundwater age at greater depth tends to be significantly higher than in shallow recharge areas. Similarly, water trapped in poorly permeable layers may be older than groundwater passing through neighboring aquifer beds because the latter is moving at higher velocities. It is clear that – on average – groundwater has to travel over longer distances between recharge and discharge zones in large aquifer systems, hence mean groundwater ages are likely to be higher in such systems.

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Solution Exercise 4

The reply to this question is specific to the individual reader and the country in which he or she resides.

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