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Disjoined PVC Casing in Borewell, Repair or Redrill Anew, Advice? : Ramamurthy Nagar, Bangalore.

We attempted drilling a borewell under the portico of a built house using flexible rig (using compressed air with the lorry standing  outside on the road) at Ramamurthy nagar, Bangalore. The rig stand was kept under the portico. The borewell driller used the PVC casing. He said hard rock was found at 100 ft and inserted the casing upto 100 ft and drilled further for another 70ft.

Suddenly it was noticed that casing was moving up and down/ going down further slowly feet by feet. At this stage it was noticed that muddy slush started coming up, which was attributed by borewell digger due to disjoining of casing at around 60 ft and because of this, loose sand was coming into the borewell and coming out in the form of slush. At this stage, driller said it cannot be continued and drilling was a failure.  Nearby water has been found at 350 ft to 400 ft depth and the hard rock is found at 100 to 110 ft.

In this case, the drilling has been done upto 175 ft only and the disjoined PVC casing is struck inside the bore.

We want to know whether it is possible to repair/replace the struck casing and continue drilling the same point till we get water?.

The 2nd question I have is if we want to dig a new borewell near to this halfdrilled damaged borewell, what is the safe distance and what method should be adapted( slow rig or flexible compressed rig?

thanks for your reply

Lakshmi Narayana

narayana_v@hotmail.com

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Comments

1. The problem faced by Lakshmi

The problem faced by Lakshmi Narayana in drilling a bore well with a flexible rig using compressed air and PVC casing pipe can be due to:

  1. Occurrence of a layer of boulders at a depth of around 60 feet damaging the casing during drilling,
  2. Failure to properly cement the casing pipes with one another while inserting into the bore well giving scope for loose material outside the casing pipe to enter into the bore well,
  3. Failure to install the casing pipe to snugly seat into the bottom hard rock leading to its movement during drilling and consequent damaged, and/or
  4. Physical damage to the casing pipe by the drill rod during drilling.

As keeping the defunct bore well in tact without sealing can lead to pollution of the nearby new bore well proposed, it is essential to seal itl. It is also not desirable to use the defunct bore well for artificial recharge of groundwater with rooftop rainwater. How such a usage had led to discharge of water with high variation in suspended solids was discussed at http://indiawaterportal.org/ask/5296 It desirable to make use of the same flexible rig used earlier to remove the PVC casing pipe installed in the defunct bore well. If that is not possible, drilling at the same site allows can be taken up to crush the casing pipe into small pieces for removal by the compressed air. Mild steel (MS) casing pipe rather than PVC casing pipe may be used for the new bore well. The casing pipe should be driven as deep as possible to a depth of 110 feet or more to snugly seat into the bottom hard rock.

The final depth of the bore well should be 400 feet or more. In case of any technical difficulty to drill the new bore well in the place of the defunct bore well, it may be drilled at any site near to it. Dr. R. Jagadiswara Rao Former Professor of Geology Sri Venkateswara University Tirupati, AP 517502 rjagadiswara@gmail.com

Dr. R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com

2.

This is in response to your second question on the drilling method to be adopted. Since the location you have mentioned is below the portico, I am not sure whether you can use a rig mounted on the lorry in this place. However, you can adopt any of the methods, but the precautions that are referred by Dr.Jagadiswara Rao have to be followed which is more important.

When you are not able to remove the casing from the borewell, drilling the bore further with the casing pipe in place would lead to presence of plastic particles in the water. I have experienced this in Hyderabad, where we had a similar situation. It took many months to obtain clear water from the borewell, and we were very reluctant to consume the water after that.

Also, use good quality PVC casing pipes. Drillers mostly use the common water pipes as casing pipes which leads to such problems. It is better to use only the rated PVC pipes meant for casing or metal casing pipes.

3.

In the case mentioned by you the aleternative is to retrieve the pvc casing and drill using Odex method in which mild steel casing be used and the bore be drilled with odex upto 120 feet and futher drilling be continued with DTH method.

Bhavnesh Sharma,
Junior Hydrogeologist,
Ground Water Organisation
Himachal Pradesh

4. How can we repair borewell - Motor fell inside

My submersible motor has fallen inside the borewell when we were attempting to take it out. So, my borewell is not working, it has failed. I want to know that how it can be repaired.

5. Useful links

Dear Mr. Yadav,

Please go through the responses in the following links:

Pump stuck in Borewell - http://www.indiawaterportal.org/ask/5318

Motor Recovery From Collapsed Borewell - Expert Help Required; Hyderabad - http://www.indiawaterportal.org/ask/9295

Regards,
Seetha Gopalakrishnan
India Water Portal Team

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