Thousands of fracked wells in Pennsylvania "may be leaking methane".

Guardian: “A study of abandoned oil and gas wells in Pennsylvania finds that the hundreds of thousands of such wells in the state may be leaking methane, suggesting that abandoned wells across the country could be a bigger source of climate changing greenhouse gases than previously thought.”
“The study by Mary Kang, a Princeton University scientist, looked at 19 wells and found that these oft-forgotten wells are leaking various amounts of methane. There are hundreds of thousands of such oil and gas wells, long abandoned and plugged, in Pennsylvania alone, and countless more in oil and gas fields across the country. These wells go mostly unmonitored, and rarely, if ever, checked for such leaks.
growing list of studies conducted over the past three years has suggested that crude oil and natural gas development, particularly in shale formations, are significant sources of methane leaks — emissions not fully included in US Environmental Protection Agency greenhouse gas inventories because they are rarely monitored. Scientists say there is inadequate data available for them to know where all the leaks are and how much methane is leaking.
Methane is about 34 times as potent as a climate change-fueling greenhouse gas than carbon dioxide over a span of 100 years. Over 20 years, it’s 86 times more potent. Of all the greenhouse gases emitted by humans worldwide, methane contributes more than 40 percent of all radiative forcing, a measure of trapped heat in the atmosphere and a measuring stick of a changing climate.
So when abandoned oil and gas wells — possibly hundreds of thousands of them in Pennsylvania alone — that are not currently included in any federal estimate for total US greenhouse gas emissionsare found to be leaking methane, the implications could be significant.
Kang directly measured leaks from the abandoned wells and found that all 19 wells in the study tested positive for methane leaks, some more than others.
She found that overall, the wells leak so much methane that if leaks from all the abandoned wells in Pennsylvania are added up, the leaks could account for between 4 percent and 13 percent of human-caused methane emissions in the state.
….Nobody knows exactly how many abandoned oil and gas wells exist in Pennsylvania, but the study says that historical records show there are between 280,000 and 970,000 abandoned oil and gas wells. Pennsylvania is the site of one of America’s earliest discoveries of crude oil, at Oil Creek in 1859, and the state is considered the birthplace of the petroleum industry in the US.
….Kang’s is one of the few studies to clearly demonstrate and quantify methane leaks from abandoned and plugged wells, said Cornell University biogeochemistry professor Robert Howarth, who is known for his research into methane emissions from natural gas operations.
When estimating greenhouse gas emissions in the US, the EPA estimates gas leakage from individual of oil and gas equipment during each step in the oil and gas exploration and production process. That method is called a “bottom-up” approach, which estimates emissions being emitted on the ground. The opposite method, called a “top-down” approach, estimates emissions based on aerial measurements taken from above sources of greenhouse gas emissions.
….Kang’s study “supports what I and many others have been saying for many years, and that’s this: There is methane leaking from oil and gas wells.” Period,” said Cornell University environmental engineering professor Anthony Ingraffea, who has collaborated with Howarth on methane emissions research and is currently analyzing Kang’s work.