Hi, Age old topic and I have read tons of posts about it but my situation seems a bit different. Everything works fine in the home. All the devices drain great. No gurgling. No dry traps. Most of the time there is no odor in the house for weeks then for some unknown reason we get this what seems like septic odor only upstairs in the loft. We use all the fixtures throughout the house except for the basement kitchen sink, laundry and bath. When the odor does occur it never seems to be emanating from any of those fixture traps. It doesn't happen after using any particular fixture either. We left for a couple weeks and when we came home the odor was very present upstairs. When we left everything had been fine for quite awhile. Nothing was being used while we were gone. At first I thought it was a bad seal on the upstairs toilet so I replaced the gasket. Even added an extra. Didn't make a difference. I increased the stack length to the max. of two feet. No difference. I replaced an expansion joint in the stack because I thought the seal might be bad. Still the same. I cut drywall off the walls to see it there was a loose of broken fitting anywhere. Couldn't find any. When I cut the drywall off the wall by the chimney I could see daylight around where the chimeny exited the roof. I sealed that up with expanding foam. No difference. I found a clean out that was a little loose and tightened it. No difference. I put a odor hog on top of the vent stack. It didn't help anything. I extended the stack another 10 feet to get it as far away from any other vents on the roof as I could. No difference. Before I did the last extension of the stack I ran a fish tape up and down the stack to see if there were any blockages. I didn't feel any. I also poured water down there while I was doing it. When we drain things you don't hear any gurgling at all. If we had a leak in the drainage system you would think you would find something wet. Nothing like that at all. If a blocked vent was the problem you would think things wouldn't drain properly or a trap would become dry so you could easily find what trap was dry but that is not the case here. Everything seems to be fine then one day the smell will be there. Its driving my wife and myself a little crazy. I'm not sure what else to try. Where the smell is strongest doesn't really have any plumbing. It seems to be strongest at the peak of the ceiling and behind the bed near the floor. There is a laundry room directly below this area and there are no smells in there. The stack does run through this area though. Any thoughts or ideas would be appreciated.

Just wondering how a well man knows when to stop drilling & call it "good"? If, for example, you hit water at 30 feet why drill farther? Do you punch into additional aquifers as you drill deeper?