I live in a rural area and have a septic system on the property.I noticed when the temp. outside is extremely cold (20 or below) there is a smell of sewer gas.it comes and goes and isnt that strong, but it concerned me since I never noticed it before.I had my tank recently pumped so I called the septic co back, the explanation given to me was sewer gas is heavier than air and in cold temps tends to drop down to ground level faster.I have no problems with slow drains or anything along those lines so everything seems to be working fine.after googling the prob I found the same explanation the septic co told me.Im just wondering if anyone else has had this issue.Its also tough to determine if the smell is even coming from my system.I have 2 neighbors somewhat close to me that could have a issue.The smells wanders and next thing you know its gone so I cant really pin point it.