We often hear about aquifers when the theme is environmental pollution but these risk being words thrown to the wind and which do not convey the idea of the danger that one is running if one does not know what these layers are, where they are and how, if polluted, they can harm us, the animals that live on the face of the Earth and the plants that grow there.
Let's go together to discover, without too much tedium or difficulty, what the aquifers are and why we must take care that are polluted as a result of activities that we ourselves, as men, carry out very often not caring about the consequences.
Groundwater: what they are
The matter that treats the aquifers is hydrogeology and we draw from this to tell what we mean when we talk about an aquifer or, equally, a water table. We mean an area of permeable rocks where there is water capable of flowing due to the force of gravity. If we investigate the origins of the word stratum, in itself, we discover that it derives from the German term falte, which means fold, in fact it is used to indicate a water deposit between the layers, therefore between the folds of the ground.
The aquifers they can also be seen as masses of water that soak the subsoil saturating the voids. They are not located randomly and do not arise from anything, they have not always been there where we find them but they were formed following theinfiltration into the ground of rainwater or surface water, like streams and rivers. One of the most important factors for the quality of groundwater is the soil, it is in fact the soil and "only" the soil that is able to filter the particles and pathogens present in the water and at the same time to retain and decompose partially dissolved pollutants.
Groundwater and underground water
The aquifers they have to do with the presence of water in the subsoil, so let's see in what forms we can find it in cases where it is not found where we identify it "by constitution", that is, always. In the subsoil we can find for example adsorption water, also known as hygroscopic, and it is water bound to the soil grains with dipolar and electrochemical bonds that cannot be moved in the liquid state. Then there is the so-called film water which, on the contrary, can move to the surface of the grains under the action of the attraction of nearby water molecules.
L'annular water it is instead what it occupies the voids between the granules, partially or totally, and has concave menisci. Subject to surface tension, annular water can be isolated if it only partially occupies the voids, otherwise it is called continuous and in this case it fills them completely, forming the so-called capillary fringe.
Among the various forms in which we can findwater in the subsoil there is also that "gravifies". In this case, it is water capable of flowing underground under the action of physical force and finally forming a water table. We have finally come to understand that not all the water present in the subsoil can be at the origin of the aquifers and circulate in the aquifers, under the action of gradients, even feeding captation works and springs.
Let's see better, step by step, how the are formed aquifers. Let's start with meteoric waters which, after falling on the surface of the Earth, in a certain part return to the atmosphere due to evaporation. What about the rest? The rest, on the one hand, feeds rivers and streams and seas, and all surface waters, on the other hand it passes through the fractures and porosities of the surface permeable rock formations, managing to penetrate the soil.
At this point, a fraction of penetrated water reconstructs the detention water which was reduced following theevapo-transpiration, but the remainder reaches deep, descends and descends towards the center of our planet, stopping as soon as it meets one impermeable formation which can be both clayey and rocky. At this point the water stops penetrating the ground and begins to settle forming areas of saturated soil called reservoir rocks or aquifers.
Let's imagine gods large tanks of water, underground, let's imagine them still but also, why not, in motion according to the permeability and position of the soil layers and the geometric conformation of the impermeable layers bordering the aquifer itself.
Note the presence of these underground tanks of water, a genuine curiosity arises to understand how much it is necessary to dig to find them, and eventually use them. In an alluvial plain if you start digging you will first encounter an aeration area, with pores partially occupied by air and partially by water, and then a saturation area, where all the pores are filled with water. A prime is usually found by digging to the inner boundary of this area waterproof and thick clayey layer. It is called groundwater or free the area between the level where the water begins to saturate the pores and the waterproof layer below.
There is also another type of water table which is defined as artesian or "under pressure". It is found deeper and is bounded both in the lower and in the upper part by a waterproof layer. If you call "Under pressure" it is no coincidence: in this area the water is really subjected to a certain pressure that allows it to rise spontaneously inside a hole dug in the ground as in the case of artesian wells that you may have already heard of. In order to have them, in Italy, in some areas it is necessary to drill at least up to 100-150 m depth.
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