JACKSON - Water wells on the Jonah and Pinedale Anticline natural gas fields were likely contaminated with hydrocarbons from trucks used to siphon water out of the wells, a Bureau of Land Management official said.

The wells found to have benzene are used exclusively by energy operators, not by ranchers, said Merry Gamper, supervisory natural resource specialist with the BLM in Pinedale.

She said the information collected so far leads BLM to believe the contamination came from "back flow" from the trucks that pull water from the wells. All the wells in the Jonah and Anticline have now been installed with "back flow preventers," which prevent anything from flowing back into the wells. Gamper said those are not required.

Other possible natural sources are also being investigated into the contamination, she said.

The BLM reported this week that benzene was found in four water wells on the Sublette County gas fields in August and September 2006. An additional 163 wells were tested this winter, showing that another 82 wells had hydrocarbons, but below regulatory levels. Those wells are being resampled. Three of the 163 additional wells had excess hydrocarbons.

"There has been no drinking water contaminated," said Rey Adame, public affairs officer for the Rock Springs, Pinedale and Kemmerer field offices of the BLM. "There is no threat to human health or livestock. There are no threats to people working in the field. I don't want to create a panic with this, because it's not. Sometimes when you go back and resample, the problem cleans itself up."

Adame said the wells were tested by a local conservation district last summer. The contamination was reported to the BLM in January, prompting the agency to get together with the Wyoming Department of Environmental Quality to test additional wells.

Adame said he didn't know why there was a delay in reporting.

"The readings were never so high it was considered a health hazard or danger," he said. "At this point, nobody thought this was an alarm. We thought, 'As a precaution, let's go ahead and do this.'"

The BLM's 2000 Pinedale Anticline Project Area document requires oil and gas operators to sample water within one mile of any exploration or production well.

According to the BLM, the BLM and DEQ will work together with operators to "develop and implement a comprehensive water well construction and operation program."

John Wagner, water quality administrator for DEQ, said he didn't think operators would be hit with fines, as the issue is still under investigation.

"At this point, it doesn't look like we have a massive problem," Wagner said. "We have indicators that we may have a problem."

Wagner said it is likely there are farmers and ranchers tapped into the same aquifer, and he is not aware of this kind of contamination happening before.

"It's not something that we go looking for too much," Wagner said. "In this case because of the (environmental impact statement) and massive scale of this development, people said, 'Hey, we should keep an eye on this groundwater.'"

Environmental reporter Whitney Royster can be reached at (307) 734-0260 or at royster@tribcsp.com.