Borewell water is yellow colour and smell

After heavy rain last year ( Oct to Dec). I have observed water colour in my borewell getting yellow and smelly. My borewell is 170 ft and septic tank and wastewater tank of my neighbour is 5ft from my borewell I have flushed borewell two times in Feb but no result still water is same yellow and smell.

What is the solution? Can I install any filters, as I don't have space for a new borewell? During flushing, water was available from 30 to 40 ft from ground. I am suspecting that the water is smelly because of septic tank water mixing. Kindly suggest solution for this.