Shale gas drilling in the Marcellus Shale had generated about 40 private lawsuits alleging water contamination, personal injury and other damages.
The legals claims would largely come from Pennsylvania, the northern state most active in shale gas exploration. The Marcellus Shale, exceeding 30,000 square miles and believed to be one of the nation's largest deposits of natural gas, also covers West Virginia, Maryland and New York.
While more than 4,000 horizontal wells have been drilled and hydraulically fractured in Pennsylvania in recent years, New York suspended drilling in 2008 to study its risks and come up with safeguards; the moratorium is expected to be lifted next year.
North Carolina is also studying the pros and cons of shale gas exploration, with a report due to the state legislature next May. Horizontal drilling and hydraulic fracturing (or "fracking") are not legal in this state but supporters want to open up the state to gas exploration in hopes of tapping an abundant resource of domestic fuel as an alternative to dirty coal and imported oil.