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

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. 
 
 
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