Motor stuck in silt : Borewell troubleshooting in Sahakarnagar, Bangalore, Karnataka

We dug a borewell at our house in Sahakarnagar, Bangalore upto 330ft with details as below:

@ 70ft Rock (plastic and GI pipe layed till 67ft)
@ 180ft first source of water struck
@ 270ft second water source stuck
stopped @ 330ft.

Now, when we opened the bore to install the motor, was surprised by seeing the motor pipe getting stopped @ 100ft. This is due to accumulation of silt from the bottom. We measured some water accumulation from 50ft - 100ft.

I would like to know how to go further to render the borewell productive at a very minimal expenditure.

Raghunandan BN