What to do if submersible pump draws muddy water from borewell ?

Submerisble pump draws muddy water even after 2 months.

I have constructed a new borewell in cuddalore district Tamil Nadu. Details of the borewell are given below:

Borewell diameter 8 inch
Casing pipe 6 inch
Borewell depth 40 ft
Water found at 18 ft
Submersible pump at 35 ft
Submersible pump 1 hp
Filter length 12 ft
Soil description Black sandy loam upto 40 ft
Please let me know, what should be done if the submersible pump is drawing muddy water.