Borewell water quality during the rains in Bangalore, Karnataka - Need solutions to remove the foul odour

I live in Bangalore (Shastri Nagar, KR Road). I have a borewell in my residence which is about 110 feet deep 4`` dia. This was drilled in 2006. The quality of water degrades immediately after rains and settles down after the rain stops. The water lathers with foul smell (visually clear however). The situation settles down after the rains have stopped. There is an lake (Yediyur) near by,  500 mts. And we have a drain at  50 mts (which will take away the overflow of lake water). Water is good in summer time, the problem is only during the rains.

Kindly provide advice on any treatment or filter to reduce the smell.

Harish Kumar. C