Need suggestion on installing a submerged motor


We have drilled a borewell 425 ft deep, which has pebbles at the depth of 80 ft. The water yield is good. We want to install the submerged motor but the borewell company says it is not advisable to go for a submerged motor as pebbles showed up at 80 ft. Diameter of our borewell is 4.5 inches (this pipe goes upto 50 ft), planning to insert the pipe till 350 ft.

Please advise whether its okay to install a submerged motor?