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.
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.
What are the 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.
What is the 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.
How charges for drilling a borewell are usually 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.
What are the 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.
What is the 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.
Normal rate:
6.5 inch bore
0-250 feet -> Rs 62
250-350 -> Rs 72
350-450 -> Rs 82
450 - 550 -> 92
550 - 650 -> 107 (Rs 15 increase)
650 - 750 -> 122
750 - 850 -> 137
850 - 950-> 157( Rs 20 increase)
950 - 860-> 177
MS Pipe(7inch dia , 2.5 mm thickness, 6Kg per cmsq strength) -> Rs 320 per feet
(3 diferent thickness: 2mm-Rs.270/ft,2.5mm-Rs.320/ft,3mm-Rs.390/ft)
PVC pipe(10 inch dia) -> Rs 300 per feet (Starts from Rs.200/feet)
MS Collar and Welding charges per joint - Rs 300 (150 for collar and 150 for welding) (every 20 feet)
61/2" Dia cap 100
Labour and Transportation charges Rs. 1000
For 950 feet bore it will take 2 days
Selecting Pump:
First read this:
How to calculate the HP of the water pump
You might have found that there are only two variables required to calcuate the water pump HP. 1) height of total lift of water 2) required flow Please take total height in meters and flow required in liter per minute. now multiply height(in meters) and flow (in liters per minute) now divide this by 4500 you will get theoretical HP of the pump.
Now there is a secret to calculate actual HP of the pump In my practical experience i did not find pump efficiency more than 30 %. In most cases it is less than 30 %. So to calculate actual HP you should multiply theoretical HP by 4. Actual HP is 4 times more than theoretical HP.
Second secret, Please calculate total suction lift from pump to sump bottom. please ensure water pump is capable of producing so much suction.
Third secret, please add 20 % to your actual height of water lift. These are called frictional losses.
Fourth secret, submersible pumps are more efficient than monoblock pump.
Mono block pump -usually Rs.15000(1.5HP)
Submersible Pump-Usually 25000(1.5HP)
Tips:
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.
Please place the borewell motor at 20 to 30ft from the bottom point of the borewell in case if the yield falls down too u will not face a problem in the water supply. if you place at 400 ft and yield is less in summer then you have to rework to down the motor further and if motor runs without water there is a risk of motor failure.
As one time effort place the motor at maximum best point. Dont look at the pipe and wire cost, Do it right at the first time, Be pessimistic for this work
HDPE Pipe: Rs.63/m (eg:270 feet Rishi brand)
Finolex cable: Rs.60/m (eg:290 feet,20feet extra)
1.5hp 15stage single phase texmo submerged nearly 25000
Total cost for 300 feet borewell 31500(Not for drilling borewell,only pump and installation charge)
Different Pump brands:
Texmo (Best in Industry)
CRI
PEW
Suguna Submersible Pump vs Monobloc pump vs Air Compressor Pump
V-Guard
What is good Water Yield: More than 2" +
http://www.derm.qld.gov.au/factsheets/pdf/water/w4.pdf
Water Tanks (Over head and Under Ground)
Best brand: Sintex
Capacity: 200litres per day is the average consumption of Indian peoples
If 4 people living in a house and every 2 days water need to be filled then 2*4*200 = 1600lires.
2000litre tanks are idle.
Price : Normally Rs.6 per litre.
So 2000 litre tank price nearly 12000
