A bore well is a well of 4 1/2", to 12" in diameter drilled into the earth for retrieving water. In this 4 1/2" and 51/2" Bore wells are commonly for Domestic purposes while 6 ½’’and more are for Commercial / Industrial purposes. A bore well is cased in the region of loose subsoil strata open in hard rock or in crystalline rock. High grade PVC pipes are used for Casing in bore wells. The depth of a bore well can vary from 150 feet to 1500 feet.
Ancient techniques utilized driving of tubes inside the earth to drill well using mud or water as a liquid media. Then after the invention of diesel engines, rotary drilling was used to remove cores out of the earth. This was called calyx method. There are several methods used for drilling Bore well. Most commonly used are Compressor Drilling, Manual Drilling and Rotary Drilling. Compressor Drilling is done with the vehicle fitted with High Power Hydraulic Air Compressor Machine. It is commonly used to drill on soil surface and hard rock. Another method is by manual Drilling or Hand Bore. This is most suited for lands with Clay or Sand. All these drillings will be at 4 1/2", 5", 6 1/2", 7" & 8 1/2" Dia. Air compressors and pneumatic drilling equipments are used to drill bore wells up to 3000 feet.
Common methods adopted for drilling borewells:
Methods of drilling to be adopted depends on factors like suitability of a method for a particular type of geological formation (i.e. such as alluvial, bouldery and hard rock), cost factors, diameter and depth of borewell and the purpose intended.
Most commonly used types of drilling methods are;
Water Jetting - Shallow bores in alluvial formations
Augur Drilling - Shallow bores in alluvial formations
Calyx Drilling - Shallow borewells in both hard rock and alluvial formation
Percussion Drilling – Deep bores in bouldery formation
Rotary Drilling - Most common method used for drilling large and deep bores in alluvial formations.
Down the Hole Hammering (DTH) Drilling – Most common method for drilling large and deep borewells in hard rock formations.
Standard diameter of borewells drilled for domestic purposes:-
For domestic purposes, 4.5 and 6 inches dia borewells are usually drilled. While 4.5 inch is most commonly drilled borewells for domestic purposes, 6 inch borewells are drilled when higher yield is required for large apartments or buildings and also for agricultural purposes. Initially larger diameter bits are used to place the casing pipes up to the hard rock zone prior to drilling specified size of the borewell.
Types of casing pipes used in borewells
Currently, PVC pipes are very widely used as casing pipe. GI/Mild steel casing pipes which were used earlier are not being recommended due to the problem of corrosion. PVC casing pipes installed in borewells must confirm to IS 12818: 1992 that governs the specification for unplasticized PVC screen and casing pipes for borewell of the Bureau of Indian standard. This standard covers the requirements of ribbed screen, plain screen and plain casing pipes of nominal diameter 40 to 400 mm produced from unplasticized polyvinyl chloride for borewell for water supply.
Slotted PVC casing pipes are used if aquifer yields through sandy zones to protect collapse of borewell side walls and to prevent entry of fine sand into the borewell which might clog the borewell. This requires detailed study by Geologists to decide slot size and at what depths these have to be provided along with gravel packing around the casing pipe.
Safe distance between a borewell and septic tank/soak pit
Maintaining sufficient distance between a borewell and septic tank is always recommended as there are chances of contamination. If the situation warrants location of them in close proximity, it advisable to properly grout the borewell casing pipe with cement slurry till hard rock formation. In shallow aquifer zones, it is not advisable to locate borewells used for drinking purposes and the septic tank in close proximity. It is better to take professional assistance in such cases to take preventive steps around the borewell as well as the septic tank.
1. Try to find 3 phase availablity in your street.
2. Do you require really 3 phase or single phase pump KW ( 3 phase deposit is higher than Single phase, I think for monthly bill be same for 3 phase or Single phase). Check with pump expert.
3. Speak with nearby house people having bore, to know about water availablity during summer. (Which helps to select the pump) Sometimes, if you go for higher suction power motor and if your bore can't yield for the motor capacity it will be problem.
4. Anyway have pipe routed to Sump & OHT with control valve. It will helps during summer time, if your bore or pump losses it efficieny.
5. Try to avoid number of bends at delivery line from bore.