Types And Features of Water Wells

So you&#;ve bought your piece of heaven and are going to build your dream home (or business) on it, but there&#;s a catch- it&#;s off the grid. No water main, no power lines, no nothing. You start ticking off the utilities: solar panels- check, septic system- check, cisterns and water storage tanks- check, water well&#; that last one sounds simple until you have to decide how it to go about creating one. So just what types of wells are there and how are they constructed?

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Well, well, well, what have we here?  

Wells provide life sustaining water for many areas that aren&#;t connected to the municipal water supply. They&#;re also extensively used as the primary source for irrigation, so in a way they&#;re responsible for the food on our plate. As important as they may be, there aren&#;t many methods for their creation. They&#;re either dug or drilled to access ground water from aquifers.

Can you dig it? And do you want to?

Dug wells date back to the Neolithic era. They were predominantly used as a source of water in Asia, Australia, and Africa. Dug wells with descending steps into the heart of the well were pretty common in western parts of India. They served as both a source of water and a place for resting. People converged inside the step wells to escape the daytime heat.

Not much has changed over the years in the way these wells are made. Dug wells are still mostly done by manual labor, but are less expensive than drilled wells, which use advanced machinery to drill through hundreds of feet of soil and rocks. In many rural areas, dug wells are still an important source of potable water drawn from shallow aquifers.

Illustration 1: Step well in Rajasthan, India

Illustration 2: From inside a step well in Bangalore, India

Structure and Limitations

Dug wells should be large enough in diameter to allow for two or more people with shovels to get into the well for digging. To prevent the soil from caving in, dug wells are lined with bricks or stones.

Dug wells are fairly low on operating costs since water is mostly hand drawn using containers hoisted over pulleys. Another beautiful tool to bring the water up is a Persian wheel. Since the depth of dug wells tends to be shallow, even if a pump is used to extract water, the energy costs are lower compared to a drilled well.

Illustration 3&4: Persian wheel and Hand drawn using pulley, rope, container

A drawback to dug wells is that in areas where underground sewer networks are absent, dug wells are prone to contamination with sewage. Dug wells are not feasible where the underlying substrate is rocky. It is also relatively more time consuming to dig a well than to drill a well. Diggers should proceed with caution as there is always the risk that the side walls will collapse during their work within the well.

Drilled wells &#; the modern day dug well

Drilled wells are used to extract water from deeper confined aquifers. They are created by drilling machines known as rigs. The rig drills a hole or a narrow vertical shaft of a certain diameter through the weathered and rock substrate. Water may be struck at multiple depths during this process, so drilling is stopped when the desired level of water yield is achieved.

A casing structure is inserted into the borehole until reaching the beginning of the rocky substrate. The casing aids in preventing soil or other contaminants from entering the borehole and thereby contaminating the aquifer. The casing pipe is not required within the rocky substrate since hard rock does not cave in. The casing pipe may be made of steel, iron, or PVC plastic. In areas with unconsolidated formations (sand, gravel, etc.), a screen may be kept at the bottom of the borehole to prevent external media from coming in.

A galvanized iron or HDPE pipe is lowered into the borehole until it hits the depth where water is available. The water from the borewell is drawn through a pump, which can be either a submersible or a mono bloc pump.

Some of the key attributes of a borewell are:

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• Depth of the borewell &#; This indicates the total depth to which the drilling was done.
• Diameter of the borewell casing &#; This can range from 6&#; to 12&#;. 4&#; and 24&#; are extreme instances.
• The casing material and the depth of the casing.
• Levels at which water was struck when the borewell was drilled.
• Static water level &#; During the borewell drilling, while the rig drills through the hard rock substrate, it will come across fissures/ cracks in the rock. From these points, water is discharged at high pressure into the borehole, causing the water level to rise up quite significantly in the borehole. After 3-5 days of drilling, the water level will stabilize- this is the static water level.
• Rating of the pump used for extracting water from the borewell.

Illustration 4: Cross Section of a borewell

Drawbacks

Deep aquifers take a longer time to recharge when compared to shallow aquifers, so borewells are not really a sustainable source of water extraction. In comparison to a dug well, it is much more expensive to drill a borewell, and the operating costs are higher since the water is pumped from much deeper depths.

Going down?

Digging and drilling a well each have their pros and cons. How much money can you afford to invest in a well? Do you know where and when you&#;re going to hit water? Is there a possibility of water contamination if you keep the well shallow? There are many factors to consider, perhaps more than you previously thought? Regardless of which method you choose, you&#;re now armed with the knowledge to confidently pick up a shovel, or know when to call for a really big drill.

You could need a drilling rig for a multitude of applications, for example to drill a well to access a natural resource (water, oil, geothermal energy, etc.), to build foundations, to make blasting holes in a mine, to take samples from the ground, etc.

It is necessary to determine what the drilling rig will be used for, as well as what kind of terrain it will mainly be operating on. Depending on the terrain, you can choose between different types of drilling rigs: rotary drilling rigs, percussion drilling rigs, down-the-hole drilling rigs, top hammer drilling rigs (with high hammer), etc.

In order to make the best choice, it is important to determine whether the drilling rig will be used for your core business or for occasional operations, and in particular whether you want to take advantage of the latest innovations or whether a machine that has proven its worth over several decades might be suitable for you.

Safety, reliability and ease of use are also important elements to consider and are directly linked to each other. A machine that&#;s reliable and easy to operate, when used according to the manufacturer&#;s recommendations, increases user safety.

It is also important to define the type of mobility you will need. There are autonomous crawler drilling rigs and truck-mounted or trailer-mounted drilling rigs that need to be powered by a generator or the truck that carries them.

Once you have determined the type of machine you need, you can calculate the size required according to the diameter and depth of the borehole.

Drilling type Soil type Comments Rotary drilling Soft rock Significant depths up to 5,000 meters
Possibility of inclined or horizontal drilling Down-the-hole drilling Hard and cracked rock (limestone, granite, etc.) Depth up to 4,000 meters Top hammer drilling Consolidated land Small diameter (150 mm maximum), shallow depth
Able to do inclined drilling Auger drilling Clay, clayey sand, gravel Depth of a few dozen meters Core drilling All soil types Drilling for soil analysis
Able to do inclined drilling Percussion drilling Hard rock: sandstone, limestone, shale Depth up to 100 meters Pipe Jacking Clay, clayey sand, gravel Installation of horizontal or vertical pipes

Rotary drilling: This type of drilling digs a hole by grinding the rock with a tool under the effect of weight and rotation. It is mainly used in oil production. The cuttings are brought to the surface under the pressure of a drilling fluid that is injected into the drill string. Drilling fluid also helps consolidate the walls of the borehole, so it is not necessary to case it as the operation progresses.

Down-the-hole drilling (rotary percussion drilling or rotary hammer drilling): this type of drilling uses drilling rigs that drill with a rotary cutter (drill head) and hammer the bottom of the hole with a pneumatic hammer. The excavated material rises to the surface under the pressure of the compressed air used for the hammer. These drilling rigs are powerful and have high drilling rates, especially in rock. For artesian wells (wells where water naturally rises to the surface under groundwater pressure) or geothermal drilling, an air injection at the end of the drill pipe pushes the water up the borehole, allowing the operator to immediately determine the water flow encountered. This type of drilling is used for hard and cracked ground up to 4,000 meters deep. When the drilling bit is eccentric, the drilling can be done with a casing advancement system (installation of tubes by gravity) which reinforces the hole as the drilling progresses.

Top hammer drilling: this type of drilling uses drilling rigs that also operate on a percussion system, but one that remains outside the borehole. They are mainly used for small diameter drilling, for example for mineral exploration or the installation of tie rods in rock. This system is used for shallow boreholes, as there can be significant deviation due to the structure of the ground drilled through. These drilling rigs can operate in any direction however.

Auger boring: This is a type of rotary drilling using a worm screw (the auger). This type of drilling is mainly used for unconsolidated clay or sand terrain. The excavated material is directly brought to the surface by the worm screw. For deep drilling, it may be necessary to regularly raise the auger to empty it of its excavated material.

Core drilling: Core drilling is similar to rotary drilling, but it uses a crown to extract a sample, called a core, inside the tool.

Percussion drilling: consists in breaking the rock by dropping a tool, the drill bit, by gravity. This type of drilling can only be used vertically. To prevent the borehole from collapsing, it is necessary to case it as it is drilled. The cuttings are reassembled as soon as they interfere with drilling by replacing the drill bit with a flap valve bailer. The flap valve bailer is a type of tube equipped with a tilting flap in the lower part. This tilting flap allows the tube to be filled with excavated material which is then transported to the surface.

Pipe jacking: is mainly used to install horizontal pipes. The tube is pushed progressively by percussion, the excavated material being removed at the end of the drilling operation either by water injection or with an auger. This technique is used in particular to avoid transmitting vibrations to the surrounding buildings or to avoid digging a trench.

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