Vertical Electrical Sounding is one of the very common geophysical methods used for domestic borewell exploration. However, sufficient open area around the location is needed for conducting the survey. Geologists charge around Rs.1,500 to 5,000/- for identifying a borewell site.
Other methods of geophysical survey are used in special cases and they are quite expensive. Local well diviners who use wooden sticks or magnetic blocks are also to some extent successful in identifying borewell sites. But this method may not be always reliable, especially in areas where the geological formation is critical.
How are charges for drilling a borewell calculated?
Charges for drilling a specified size of borewell include
drilling cost per feet,
cost of casing pipe per feet,
cost of drilling and installation charge for casing pipe per feet,
flushing charges per hour for flushing the borewell after drilling and
transportation charges of the rig to the site from nearest town per km.
Drilling rates are sometimes charged in slabs for specified ranges especially when deep borewells are drilled. As drilling rates usually vary depending on the availability of rigs, local demand and site conditions, it is better to cross check with few drillers to get a competitive quote.
Is there a best suited time for drilling a borewell?
As such there is no prescribed season for drilling a borewell if the location of site has adequate ground water potential. However, identifying a suitable site and drilling the borewell in summer months would give the worst possible scenario in the location at the point of time.
Therefore, summer months are usually preferred by some experts as the best suited period for drilling a new borewell. Also, as most agricultural sites can be accessed by drilling rigs only during summer months, they are usually available in these periods.
Can borewells be drilled inside an existing well?
Dry wells can be brought to use by drilling borewells inside them. It is mostly done in large wells used for irrigation purposes. Flexible rigs which have separate tripod and drilling head, can be used for drilled a borewell inside an existing well if it is above 3m x 3m size to accommodate size of the rig and working space. These rigs are capable of drilling up to a depth of around 300 feet.
Is it safe to drill a borewell very close to the house?
Submersible pump or pipe assembly stuck in a borewell can be removed in most cases using various types of fishing tools. After determining the position of the objects struck in the well, water is poured into the borewell to loosen the earth covering the pump or pipe struck inside the borewell before using fishing tools. Borewell rehabilitation agencies or mechanics usually develop special fishing tools that can be attached to the grounded pumps or pipes in a borewell based on their experience. Usually, this may be a time consuming and expensive attempt which may not be always successful. The entire operation may some time be a catastrophe that can lead to complete damage of the borewell; therefore adequate caution must be taken before deciding upon such an exercise.
Which types of pumps are suitable for borewells?
Jet, compressor and submersible pumps are the widely used pumps for domestic purposes in India. Jet pumps which are installed above the ground level over or near the borewell are suitable for depths upto 150 feet. If the ground water is at lower depths submersible or compressor pumps are used.
Compressor pumps are suitable for low yielding borewells and also they are easy to install and maintain as they are installed at ground level. However, they are noisy and may also require frequent repairs.
As submersible pumps of 4” dia which can work in single phase electricity connection are available in the market now, these have become a preferred choice for domestic borewells. They can be installed for meeting higher water requirements. However, submersible pumps will be prone to frequent repairs if they are installed in the borewells containing heavy silt particles.
How to choose a right type and capacity of pump for a borewell?
Capacity of the pump to be chosen depends on the depth at which the pump/foot valve is to be installed and the desired discharge. Based on the total depth of the borewell, the depth at which the pump is to be installed (usually 10-25 feet above total depth of pumps) is decided.
The total head is determined using the depth of pump, over head tank level and friction loss expected in the suction and delivery pipes. Using the total head and the discharge desired, from the pump rating curves for each models of pump anufactured by various companies, the right HP of the pump suitable can be selected.