ERIE – After more than two years, Wendy Leonard finally gave up on Erie and moved to Louisville. Erie, she says, made her family sick, because of all of the natural-gas drilling in and around the town.

The mother of four children, Leonard knows she can't confirm that her family's health problems are linked to the drilling.

"Until we have a health impact study to prove one way or the other, we don't know," Leonard said. "But I think there's something going on."

Leonard is one of a growing number of Coloradoans who live near oil and gas wells and contend they have suffered from headaches, bloody noses, stomach pain and nausea.

Such complaints have cropped up on occasion over the years, but have intensified along the Front Range and elsewhere in the state with spread of hydraulic fracturing, a contentious technique that involves pumping water, sand and chemicals into a drilled hole to free oil and gas trapped deep below ground.

The oil and gas industry says these reports of health problems are part of a mass hysteria that it contends has swept the nation.

Indeed, no study has been done that offers any clear evidence supporting the notion that fracturing is making people