CHEYENNE - Some coal-bed methane water flowing into the Powder River of northeast Wyoming contains potentially dangerous levels of ammonia, according to a study by the U.S. Geological Survey.

But the study also found that vegetation in a drainage channel can absorb dissolved ammonia, and microogranisms can transform it to harmless nitrogen gas.

Ammonia, a form of nitrogen, is a colorless gas that can be toxic in high amounts.

USGS scientist Richard Smith, who led the study, said the findings shouldn't warrant halting coal-bed methane operations in northeast Wyoming because the study looked at only one of the many drainage channels flowing into the Powder River.

"It's not so significant that it would be raising a red flag or anything, but it is something that folks should be aware of and perhaps disposal practices should be designed a little bit more along the lines of taking care of the nitrogen," said Smith, who's based in Boulder, Colo.

Billions of gallons of water from underground aquifers are pumped to the surface in order to recover the coal-bed methane, or natural gas. Impounding the CBM water in ponds and letting the water runoff into the ground are the two main ways that gas producers dispose of the water byproduct.

Some of the discharged water in northeast Wyoming's Powder River Basin is high in sodium and other salts, which can ruin crops and soils and harm fisheries.

Smith said more study is needed to determine what happens to the ammonia after it enters the Powder River and how the practice of impounding the coal-bed water affects ammonia levels.

"We didn't follow (the water) after it went into the Powder River," he said. "Presumably it would have been diluted as it entered the Powder and probably dissipated in the Powder, but we didn't actually follow it that far."

The quality and quantity of the water discharged in Wyoming has been an issue with environmentalists and the state of Montana, where the Powder River flows from Wyoming.

"We have quite a few concerns with coal-bed methane development, including the way that the water is handled and the salting of the soil, that sort of thing," said Ashley Roberts, state organizer with the Powder River Basin Resource Council in Sheridan. "But just in general, protecting groundwater is huge and so if ammonia is going to be a contaminate or is going to be coming up the wells and causing a public health issue, then that's definitely a concern for us."

Industry and Wyoming regulators say the water isn't as bad as detractors say and has proved valuable to some ranchers and farmers for watering stock and farms.

Monica Dermodi, director of the Coalbed Natural Gas Alliance, declined comment, saying she and industry operators she had spoken with had not seen the report.