Sewage water mixed in borewell

Need info on cleaning of borewell water which got sewage water mixed into it.


We have our 100ft borewell dug in 2013. Recently our drainage got clogged and the sewage water got mixed in our borewell. Now the drainage clogging has been cleared but still the borewell water is contaminated and the water yield is very less. Is there any ways to clean my borewell? Please suggest.