Borewell water contaminated with sewage water

I have a borewell dug upto 1000 ft and the opening of the casing pipe is 2 ft below ground level. I made a manhole and covered it. The borewell is in front of our gate and below a car ramp.Unfortunately, the domestic sewage pipe passing besides this has broken and the water entered into borewell. Since then, the bore water is emitting stinky smell. I pumped out water daily for an hour. Dropped chlorinated water into the borewell twice. As I pumped out water daily for 2 weeks the smell has gone. Later I intermittently used the borewell for 5 minutes for a couple of days in a week. Now the water is started emitting foul smell. There is no leakage of drainage found. Pl advise.