Even if we drill boreholes for 1000 feet or 1500 feet the aim to reach groundwater should be scientifically recognised. If we make a mistake in marking, the entire investment in borewell drilling cost will be lost.
Even if there are a plethora of equipment’s with borewell contractors to identify borewell drilling locations in today’s technology, the procedure, vocabulary, formulas, scope, and technical analysis should all be followed to ensure borewell drilling service to be success. In reality, it consists of various methods ranging from the most basic – but still useful for people or small communities with limited resources, such as dowsing – to the most sophisticated, such as prior analysis of satellite photos or proton magnetic resonance (PMR) investigations for big borewell contractors.
The purpose of this document is not to provide detailed explanations of the mode of operation and application of the various techniques, as the majority of them are quite expensive and can only be used by specialists in borewell services. Instead, it seeks to explain the basic principles, as well as the main benefits and drawbacks of the techniques, so that the communities and people affected can learn about their main characteristics and be prepared and can save money in borewell drilling cost or in borewell cost per feet.
The search for groundwater sources must consider both technical (hydrogeological) and socioeconomic criteria (closeness to a village, cost of investigation). In reality, proximity to the beneficiaries is frequently the most important criterion. There are several approaches to investigating phreatic layers. Dowsing was the only method of searching for groundwater in the past for borewell drillers . More modern and scientific techniques were developed as a result, significantly improving the success rate of water collection facilities of the borewell services.
a) Initial survey
It is highly recommended that phreatic layer investigators conduct preliminary surveys, especially if they are not from the region in question, in order to collect information that can provide them with valuable data on the locations where water is likely to be found. It can save your borewell cost per feet. Depending on the size of the expected source, this could be:
– Following a preliminary inspection of the site and a meeting with the chiefs or heads of the villages, a survey of their population to determine where wells would have been dug or springs would have been used, where the vegetation is greenest and remains green during the dry season, where trees and plants naturally grow.
Certain people in many countries (including France) have the ability to investigate and determine the presence of water on a site, as well as detect water channels (veins, faults and aquifers). These “dowsers” are frequently people who have inherited special abilities from their forefathers or a village wise man or woman. The principle is as follows:
– Using metal rods or a forked or Y-shaped twig from a tree such as a mango tree
c) Modern techniques
These methods allow for more precise aquifer location, as well as much more efficient assessment of aquifer size, volume, quality, and sustainability and save money in borewell cost per feet.
The presence of water can be determined by analysing maps and local vegetation. A global geological analysis can even be carried out in the case of large-scale investigations by interpreting satellite images or aerial photos. These can draw attention to the presence of major geological outlines that are likely to give rise to fractures with identifiable directions or outcrops.
Geophysical methods are now the most commonly used methods for investigating and detecting underground aquifers. The method used is primarily determined by the geological context.
Traditional geophysical techniques
We use these methods to investigate the physical properties of soil, particularly its electrical properties. Aquifers are frequently trapped between rock layers. All rocks conduct some electricity, but their conductivity and resistivity differ depending on their type: compact rock, dry rock, fractured rock, wet rock, permeable structures or impermeable structures. The electrical resistivity of a material is its ability to oppose the flow of electric current. These methods are thus based on the soil’s or rock’s ability to conduct electricity and the measurement of their conductivity or resistivity (the opposite of conductivity). The type, size, and quality of the aquifer are deduced and specified from these measurements, or perhaps only assumed, but with a high probability. There are two main types of methods, which are sometimes used in tandem: a) direct current measurement of electrical resistivity.
This is the most commonly used method because it is applicable to the widest range of situations. It entails using two electrodes to direct current into a geological structure at a specific location (50 to 400 volts depending on its resistivity – conductivity) (A and B). There are numerous electrode arrays that could be used ( Schlumberger, 4 terminals, etc.). The investigation area should not be too large, and it should be relatively flat and free of buildings that could cause interference and make it impossible to have AB lines of the required length (over 300m).