The federal government is warning residents in a small Wyoming town with extensive natural gas development not to drink their water, and to use fans and ventilation when showering or washing clothes in order to avoid the risk of an explosion.

The announcement accompanied results from a second round of testing and analysis in the town of Pavillion by Superfund investigators for the Environmental Protection Agency. Researchers found benzene, metals, naphthalene, phenols and methane in wells and in groundwater. They also confirmed the presence of other compounds that they had tentatively identified last summer and that may be linked to drilling activities.

"Last week it became clear to us that the information that we had gathered" "was going to potentially result in a hazard -- result in a recommendation to some of you that you not continue to drink your water," Martin Hestmark, deputy assistant regional administrator for ecosystems protection and remediation with the EPA in Denver, told a crowd of about 100 gathered at a community center in Pavillion Tuesday night. "We understand the gravity of that."

Representatives of the EPA and the Agency for Toxic Substances and Disease Registry, which made the health recommendation, said they had not determined the cause of the contamination and said it was too early to tell whether gas drilling was to blame. In addition to contaminants related to oil and gas, the agency detected pesticides in some wells, and significant levels of nitrates in one sample -- signs that agricultural pollution could be partly to blame. The EPA's final report on Pavillion's water is expected early next year.

ProPublica first drew attention to Pavillion's water in late 2008, and reported extensively on the EPA's ongoing investigation there last August.

EnCana, the oil and gas company that owns most of the wells near Pavillion, has agreed to contribute to the cost of supplying residents with drinking water, even though the company has not accepted responsibility for the contamination.

EnCana spokesman Doug Hock told ProPublica in an e-mail that the petroleum hydrocarbon compounds the EPA found "covers an extremely wide spectrum of chemicals, many of which aren't associated with oil and gas."

"ATSDR's suggestion to landowners was based upon high levels of inorganics -- sodium and sulfate that are naturally occurring in the area," he said.

EPA scientists began investigating Pavillion's water in 2008 after residents complained about foul smells, illness and discolored water, and after state agencies declined to investigate. Last August the EPA found contaminants in a quarter of samples taken during the first stage of its investigation, and the agency announced it would continue with another round of samples -- the set being disclosed now.

In the meeting Tuesday, the agency shared results from tests of 23 wells, 19 of which supply drinking water to residents. It found low levels of hydrocarbon compounds -- various substances that make up oil -- in 89 percent of the drinking water wells it tested. Methane gas was detected in seven of the wells and was determined to have come from the gas reservoir being tapped for energy. Eleven of the wells contained low levels of the compound 2-butoxyethanol phosphate -- a compound associated with drilling processes but that is also used as a fire retardant and a plasticizer.

The scientists also found extremely high levels of benzene, a carcinogen, and other compounds in groundwater samples taken near old drilling disposal pits. Some of the samples were taken less than 200 yards from drinking water sources and scientists expressed concerns that the contaminated water was connected to drinking water wells by an underground aquifer.

"The groundwater associated with some inactive oil and gas production pits" "is in fact highly contaminated," Ayn Schmit, a scientist with the EPA's ecosystems protection program, told residents. But she also cautioned that the EPA has not determined the cause of the contamination and is continuing its investigation.