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Solution for boulders in a borewell - Begur, Bangalore

Submitted by sasi_ranga on June 6, 2010 - 17:15

Dear All,

I request some of you to give solution for my problem and the details are given below.

  • Location: Begur, South Bangalore
  • First borewell depth - 350 feet
  • Second borewell depth - 550 feet (Lacks water but presence of wet pores at 350 feet, possibly a seasonal aquifer)
    • 2 inches of water between 550-580 feet
    • Presence of boulders at this depth (2 or 3 in number around one inch thick)

We stopped drilling at 630 feet guessing the boulders may increase.

We have been adviced to install stilt pipes for throughout the 630 feet which I felt is very expensive after spending 1 Lakh already for this 630 feet borewell.

I have 2 questions

  • Would the presence of boulders cause any potential problem? If yes, any solutions to counter the same
  • What kind of submersible pump I need to use for this kind of scenario and at what level I need to place the pump?

Request for an answer and Thanks in advance

Sasikumar

Bangalore

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Comments

1. solution for boulders

Submitted by wellwaterworks on July 11, 2010 - 19:08.

Dear Sasikumar,

If you do not install a slotted casing right down to the base of the well, it is quite possible that you borewell gets filled up to the level where you struck the boulders. Maybe it rises slightly above that point.

You could go in for a regular submersible pump and lower it down to only 520ft. try to modify the base plate of the pump so as to attach a strainer which is tapering downwards like a cone and having a diameter slightly smaller (half an inch) than the diameter of the borewell. If the hydrostatic pressure is sufficient the water level will rise well above the level at which the pump is installed and you can pump it out without facing any problems. The strainer will keep the boulders from rising up and jamming the pump.

This would ensure that when the pump needs to be removed it can be easily pulled out

Another option is to use a 5 hp borewell compressor pump and lower the pipes right down to the full depth of the well, as there are no movable or costly parts inside the borewell, it is safe to use, thought the efficiency of this system will be considerably lower.

But you have to keep in mind that once installed you cannot remove this assembly as most probably the bore will have collpsed and encased this pipeline assembly.

All the best...

2. Solution for boulders

Submitted by Neeeradhan on August 13, 2010 - 21:56.

Hi Sasikumar,

As you said there is 2" water and your requirement comes below 4000- 5000 LPH  you need not worry about the presence of boulders. Anyway pl. do not lower the pump beyond the level at which boulder is struck, atleast keep 5 ft. clearance.

If you are damn sure that there were no boulders present at 350 ft zone  you can install a 4" submersible pump of 5 HP 30 - 36 stages with 1.5" delivery size.

If water is insufficient and  the pump gets dry run occasionally, an automatic panel board can also be installed.

It is more safe to install a compressor pump since there is no inner casing erected and since the first water strike was after the half depth of the well. (Compressor Pumps will give max. efficiency in borewell having the following two features.

  1. The Borewell should be dry while drilling upto half the total depth. 
  2. There should be more water  than the double of the delivery pipe).

Lets hope for the best.

Arghyam