A gas well leak through a quarter inch hole in the valve spread 80 miles down causing throat irritation and rotten egg smell. It is estimated that 135,000 cubic feet gas leaked before it was noticed and arrested. It is reported that the smell is due to high level sulfur compounds in the mercaptans collected in the gas at the well.
The reason for spread of gas so far is stated as "combination of a light south wind and an inversion of cold air trapped below low clouds with warmer atmosphere above the clouds prevented the gas dispersing upward and caused the gas to be closer to the ground, spreading the gas so far north".
Normally, when software models are used for particular weather conditions, we get dispersion distances which appear to be on higher side. "Experts" in the field too question such results stating that they are illogical. But, this incident is warning to users, emergency responders and regulators to be conservative on distance of impact and take protective measures in the area falling under this.
Grayling gas leak smelled 80 miles away
http://www.petoskeynews.com/gaylord/news/ght-n-gasleak-122811,0,693297.story