GLENWOOD SPRINGS, Colo. (AP) -- Colorado oil and gas regulators are investigating after a carcinogen was found in the drinking water at a cabin.

The Colorado Oil and Gas Conservation Commission issued a Notice of Alleged Violation to four energy companies after tests found benzene water at the cabin outside Parachute in western Colorado.

The notice blames the benzene on a waste discharge and says one person went to a hospital with throat problems after drinking the water.

One of the companies, Williams Production RMT, says the source of the contamination hasn't been identified but the company is taking remedial steps.

Marathon OIl Co. says its only wells in the area aren't in production but the company is investigating.

Petroleum Development Corp. said Monday it drilled two wells in the area but turned both over to Marathon. Petroleum Development says it's cooperating with the commission and the other companies in trying to identify the source of the release.

The fourth company, Nonsuch Natural Gas, had no listed number.