Kitchen has a double sink. The right side has the disposal and the left side has the trap. Both sink pipes enter separately into the wall. When the disposal is turned on, the water backs up into the left side of the sink and also smells like sewer. What is happening and what can I do about it?

Kitchen has a double sink. The right side has the disposal and the left side has the trap. Both sink pipes enter separately into the wall. When the disposal is turned on, the water backs up into the left side of the sink and also smells like sewer. What is happening and what can I do about it?

Your sink has a blockage in the lateral line in the wall. Remove the "J" bend from the trap and send a snake up into the wall.
The good news is that you shouldn't have to put out more then 6 or 7 feet of snake. After, flush the line out with a sink full of hot water. Good luck, Tom