It is clear that well development and construction was not done properly. A professional driller prepares litholog,time log and variation in the hammer sound and decides about insertion of blank and slotted casing pipe. This practice was in vogue, even when drilling has been carried out in hard rock terrain.
One needs to ensure that both the above operations are done to ensure success. In these operations first check whether the casing pipe has been anchored properly or not.
Contributor: Dr. P Ramachandra Reddy (https://www.indiawaterportal.org/users/paravata)
Reasons and remedies for the silt accumulation in the bore well are,
1. Shallow water carrying silt moves vertically downwards into the bore well along the annular space between the casing pipe and the surrounding geological formation. Construct a trench around the bore well till hard rock is reached and fill it with concrete.
2. Loose formation occurring in between the end of the casing pipe installed and hard rock at depth contributes the silt. You have to install a 5"-diameter blank casing pipe from surface till hard rock is met at depth. You have to then flush the bore well to remove the silt accumulated and install the submersible pump.
Contributor: R Jagadiswara Rao (https://www.indiawaterportal.org/users/rjagadiswara)
Source: https://www.indiawaterportal.org/ask/5591