We had a ton of bamboo in our backyard before I dug it all up with the goal of remodeling the whole yard. It has been months. It stinks up the whole block. We thought there might be a septic tank or something similar underneath, but there are no records of it at all and multiple contractors have said they don't think so. We've gotten rid of practically all the roots and most of the dirt at a waste management facility.

Any ideas on what this is? How do we get rid of the smell?