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It may happen to hear about artesian well and of phreatic well but what's the difference? I bet that not many people ask, also because I must admit that to understand it it is necessary to rise to a rather technical level. Without pretending to become experts, without even wanting to replace those who deal with them for work, let's try to tell how these wells are made, what characteristics they have and what they are for.
To begin to get an idea of what we are about to talk about, we can say that the water table is in a certain sense the classic large diameter well covered in stone or with overlapping concrete rings. And the artesian well? It has a much smaller diameter and must be excavated with one auger. From the hydrogeological point of view it is not the perfect way to define them but let's start with these two definitions to understand that we are facing two different types of wells that should not be confused.
Artesian well: what it is
In this article we want to give more space to shaft with smaller diameter, to the artesian one. So let's define it as a well in which water flows naturally, without the help of mechanical means such as submerged pumps. Magic? No, not at all, preferring to say human cunning, in the positive sense of the term. The wells defined in this way draw water from one stratum called artesiana from which they then take their name. It consists of a layer of water placed in depth and in this case the water flow is a consequence of the pressure exerted on the water by the two impermeable layers that delimit the aquifer itself, above and below.
Artesian well: what is it for
Now that we have seen that there is no magic behind the artesian well, let's see how it is used. We have seen that there are cases in which the water is able to rise by itself, at least until it reaches the so-called piezometric line, or the point where the water pressure is zero. This is where the artesian wells they are come into play wells of modest diameter but which perforate the upper part of the aquifer to cause the water to rise upwards, up to the static level of the aquifer itself.
They practically help the water to travel "the last mile" in order to allow it to gush into the soil. Everything is calculated, everything must be calculated from time to time also because the rising water it is conditioned by the pressure in the water table. This is how it works: the water rises to the surface more easily if the pressure is high.
Artesian well and phreatic well
Let's go back to the difference between artesian well and water table by correcting what we stated at first only to begin to show that they are two different wells. We have illustrated them focusing on their diameter but this is not the distinctive element as neither are the construction methods and the depth of the drilling. The real difference between the two wells in question lies in the characteristics of the intercepted aquifer.
Let's see how it works, it's not as difficult as it may seem. When you go to "fish" water that circulates between two impermeable layers of soil, we speak of artesian well, on the other hand, when there is an aquifer in which porous rocks are present and the water circulates uniformly throughout the ground, then the well is decidedly phreatic.
The diameter, and the other characteristics listed above, are mere consequences of this distinction. But we can now say what we mean when we talk about large diameter or small diameter well. In the first case, these are wells that do not exceed 10-20 meters in depth and are used to capture surface aquifers. The small diameter wells, the artesian ones, can instead go down even more than 100 meters just to reach the aquifer in which the water is located.
DIY artesian well
It is by no means trivial to build a artesian well alone, special equipment is needed but above all it is necessary to know the specific techniques and characteristics that it must have depending on where we want to make it.
Let's see broadly how we should proceed. First of all you should make one test perforation to locate the water table, digging with a drilling machine that makes a small hole. When the air begins to rise to the surface, it also comes with solid material that is very useful for evaluating the stratigraphy and choosing the specific equipment to make the well.
Usually a drilling machine equipped with a toothed chisel is used that can also drill into rocks. While digging is pumped bentonite mud taken from a tank dug into the ground which, rising to the surface, prevents the walls of the well from giving way. When digging reaches the pitch, a pipe is inserted in the hole, to complete the work, on one side a siliceous gravel in the interspace between the walls of the hole and the pipe, on the other, on the surface, cement is placed to prevent surface sewage from penetrating into the well. Last operation: to purge the well by extracting the bentonite mud to then insert the submersible electric pump with its delivery pipe.
Artesian well: price
The cost of making one cannot be estimated artesian well a priori without knowing the composition of the soil, the materials and the depth of the excavation to be carried out. The price may also vary from company to company and from area to area. Let's try to make some estimates specifying that they are only indicative and do not purport to be a market survey.
A shallow well could cost you from 2 thousand to 3 thousand euros, if the land does not create problems and neither does bureaucracy. Things can get complicated, and prices can go up, if it is necessary to dig to a particular depth to reach the useful aquifer, or if the ground in which you operate is particularly rocky. To give an idea of prices, in the worst cases a artesian well it can also have a drilling cost of 90 euros per meter.
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