Easiest way to find borewell

Hello Experts,

My question is an unusual one. 

Around 7yrs back at my farm in the area of around 400 sq meters, we dug two borewells (Each around  - 450meter deep - 08 inch diameter). It was in the night, therefore borewells were properly covered. 

I did not visit the place until last month. Found 1 Borewell, but can not find another one. We put lot of efforts, gently used JCB to clean area move soil, but no luck. What is the easiest way to find the borewell please?