Methane in groundwater is more likely to come from naturally occurring coal seams than oil and gas development in northern Colorado, according to researchers at the University of Colorado Boulder.

They analyzed state data gathered in the Denver Julesberg Basin between 2001 and 2014. The majority of water sampled had concentrations at or below the limit set by the state regulating agency. 18 percent of water wells sampled showed naturally occurring methane from coal seams in the ground. About 5 percent had methane related to oil and gas development.

“The big goal of our project is to provide more information to make good decisions about oil and gas development and its regulation," said Joseph Ryan, co-author of the study.

The Colorado Oil and gas Conservation Commission is in charge of that regulation. The agency said it works with operators to investigate and find solutions when methane gets into groundwater. 

COGCC officials say the study illustrates the importance of current monitoring efforts. 

Ryan says low concentrations of methane in water aren't harmful to human health. But extremely high concentrations are flammable and could lead to explosions.

Editor's Note: An earlier version of this report misstated how many groundwater contamination cases a year are connected to coal seams. The current version is correct.