Sewage water mixing with borewell water

Advice needed

My borewell is located near to the compound wall. After few days of borewell drilling sewage started to get collected on the nearby plot which is hardly 3 feet from the borewell. We drilled for 200 feet. Water levels in the nearby borewell are < 50 feet. We used casing pipe for 35 feet after that pipe didn't go. Once the water collected in nearby plot the water level in the borewell raised. The level of water in the borewell is almost same as the outside sewage water. When we run the motor the water level in the borewell didn't reduced. When contacted to the borewell person he asked me to insert one 6inch pipe inside the existing 10inch pipe. Will this solve my problem. I feel that the sewage water will go into the 6inch pipe. Please suggest.