6.1. Aquifers and Groundwater

Aquifer definition: A permeable geological formation that contains water. Both conditions are necessary. The formation needs to contain water and the formation needs to be sufficiently permeable so that the water can move within the formation. Such formations are usually soil layers (sand, gravel, cobblestones) or strongly cracked rocks, or karstic formations.

There are two types of underground aquifers:

1. Unconfined aquifers: They have as their lower limit an impenetrable geological layer while their upper limit is the free surface of the water (well horizon). Schematically shown in blue in Figure 1.
2. Confined aquifers: They have an upper and upper impermeable geological layer. The water is under pressure.

What are artesian wells?

Artesian wells: They are drillings in places where the ground is lower than the well horizon of the limited aquifer. The water reaches the surface on its own. We do not need to pump it.

Q. Mention five advantages of groundwater over surface water

1. Απλή λύση για ύδρευση/άρδευση. The use of groundwater is a relatively economical and fast solution for serving the water and irrigation needs, especially in small areas.
2. Δεν απαιτούνται έργα αποθήκευσης. The aquifers behave as super-regulated reservoirs, with the consequence that the construction of large storage projects (dams, reservoirs, reservoirs) is not required for the utilization of groundwater.
3. Δεν απαιτούνται μεγάλα έργα μεταφοράς. When aquifers grow below the areas where they are consumed, the construction of large transport projects is avoided.
4. Είναι δυνατή η σταδιακή ανάπτυξη. Drill bits can be constructed gradually depending on the increasing needs. Therefore, it is possible to gradually develop the drilling system and reduce the initial cost of the investment.
5. Υψηλή ποιότητα νερού. In areas where the aquifer has not been polluted (eg by pesticides) the water quality is very high and no significant treatment is required

The amount of groundwater on earth is 60+ times greater than the amount of surface water. However, these huge amounts of water cannot be utilized because:
1. They are at great depth
2. They are not found in porous formations.
3. Their replacement rate is slow (environmental consequences in case of extensive use)

Main features of an aquifer are:

1. Surface (km²)
2. Thickness (m)
3. Porosity (n)
4. Hydraulic Conductivity (K), Specific Yield (S_y)

Based on the above we can calculate:

1. The amount of water is in an aquifer.
2. The amount of water we can pump for a given humidity of the aquifer level.
3. To locate the best location for drilling new wells.
4. Assess the extent of possible water contamination.