Pumping of fossil groundwater in arid regions

50 L/s groundwater of the following composition (Table 35) are extracted from a well in an arid zone. 

It is known that only a small amount of the extracted groundwater originates from recent groundwater resources (Table 36). The rest is extracted from a reservoir of fossil water that has been formed 20.000 years ago when temperatures were considerably lower in that area than they are today. 

The fossil water is characterised by high total mineralization as a result of long residence times in the subsurface as well as by lower 2H and 180 isotope values as a result of the lower temperatures during formation (Table 37). The different amounts of 13C can be explained by the establishment of equilibrium of the fossil groundwater with marine limestones with higher amounts of 13C than recent groundwater, which reflects the lower concentrations of 13C in the atmosphere. 

If the amount of fossil water in the extracted groundwater is known an estimation can be given on how long it will take to completely exploit the approximately 5 m high, 1 km wide and 10 km long reservoir assuming a constant rate of production of 5 L/s. 

Note Remember the explanation in the introduction of chapter 3.1.4 that the portions of several initial solutions on the final solution can be modeled with the help of the inverse modeling  

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