Borewell drilling in soft rock conditions in Bangalore, Karnataka - Need advice on pump selection, casing and further drilling

We have implemented a 6.5 inch borewell in Vidyaranyapura, Bangalore a few days back. The area is known for loose soil because of proximity to the lake bed. Loose soil was encountered till 90 feet and soft rock (white color ) from 90 to 200 feet. MS casing was laid toll 90 feet. Boulders were found from 90 to 300 feet. Water at 100 feet, around 1.5 inches was also struck. Drilling was halted at 300 feet and 5" PVC pipe was inserted, but only till 115 feet as the boulders and water prevented further insertion.

The driller suggests the placement of a submersible pump at 105 feet. On further questioning the driller currently plans to re-evaluate the depth and use high pressure air/water to clear the blockage. But he cautioned that this might in some cases damage the casing. And that depth reduction could be due to the soft rock/silt collapse.

My questions are as follows:

1. Is it worth investing further funds on pumps etc in this well?
2. Is slotted PVC a good solution in the current situation?
3. Should the MS casing be removed and re-insertion attempted till 300 feet?
4. Is it necessary to drill till we reach hard rock?

Thanks!

Kiran