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Casing to address gaps in water source ? - Bangalore

We recently drilled a borewell - 6inch diameter and hit water at 340 feet. While drilling the borewell, there were small discoveries of water at 120 feet and also at 180 feet. We continued drilling upto a large water table was reached; which we hit at 340 feet.

A metal casing was installed upto 105 feet.

The borewell company now says that an inner casing (PVC) of 340 feet has to be laid to ensure that the borewell does not collape because of the gaps found at 120 feet and at 180 feet.

They claim that the casing will ensure long life of the borewell and safety of the motor. Since this is going to cost quite a bit of money, we would like to take an expert opinion if the casing is really required.

The borewell company also says that the inner casing has to be laid within a week's time of the initial drilling to avoid total collapse of the bore.

Please suggest!

 

 

 

 

 

 

 

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Comments

1. Casing to address gaps in water source

Dear Rajaram,

If there was loose and friable material encountered at the depths mentioned where you struck small quantity of water then it is right that one should install the inner casing. and the reason given is also true that it will prevent the fine sand etc, from entering into the well and fill up the borewell and also jam the pump, but if there was no soft or friable material encountered then installing this casing will not be needed.

But this Inner casing can be installed at a later date but before the pump is lowered in the borewell. If the material is to collapse and fill up the borewell it iwill happen when the pump is installed and the borewell is dewatered and water along with fines material starts entering the well from the surrounding area. 

Actually, a casing with proper screen opening and a gravel pack around this pvc casing is what ideally should be done.

Only you and the drilling company know what kind of material was encountered while drilling, hence  the decission to take the risk of not installing the casing is yours to take.

All the Best

Anil Lalwani

www.wellwaterworks.com

 

2. Dear User,Season's greetings

Dear User,

Season's greetings from Hyderabad!

If the bore well is located in Bangalore, deeper casing requirement arises in deeply and intensely kaolinized or epidotized zones in which case the driller might have encountered certain difficulties in drilling to a depth of 340 feet. You may kindly post the driller's log (Exact location, diameter of the bore well-6inches, Time versus depth with comments on nature of rock being drilled and yielding zones, "V" notch readings, and the duration of flushing after drilling the last foot, final "V" notch and water level readings and details of the "V" notch itself (angle and installation details, Time versus "V" notch readings) to help us to give appropriate response.

Did any qualified Hydro-Geologist attend to drilling? If not, soil/rock samples collected depth wise can be examined by any experienced Hydro-Geologist for giving guidance on such problems.

Assuming that there is need for inserting the casing pipe to a depth of 340 feet, inserting PVC casing pipe now means reduction in effective diameter of the bore well. That may pose problems in deciding the specifications of the pump to be installed.

One hopes that the bore well was drilled after getting due clearances from the concerned Authorities as per the prevailing rules and regulations.

C. Udaya Shankar 
Geologists

3. Possible to have inner casing at the desired depth

Sir, it is possible to have the inner casing at the depth where the problem occurs especially at 120 to 180 feet

Saravana borewell fishing works,
kunnathur.(Tamil nadu)
09842204294
prop: R.Sekaran.

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