By Jon Hurdle

PHILADELPHIA (Reuters) - U.S. government officials
urged residents of a Wyoming farming community near natural gas
drilling sites not to use private well water for drinking or
cooking because of chemical contamination.

"Sample results indicate that the presence of petroleum
hydrocarbons and other chemical compounds in groundwater
represents a drinking water concern," the Environmental
Protection Agency said in a statement about tests of 19 water
wells around the town of Pavillion.

The Wyoming investigation precedes a national study by the
EPA into the safety of the drilling technique known as
hydraulic fracturing or "fracking", in response to concern in
Congress and in some communities near gas rigs in many states
that human health is threatened by the process.

The tests in Pavillion found that 17 of the 19 wells tested
contained petroleum hydrocarbons as well as napthalene, phenols
and benzene, the Environmental Protection Agency said in a
report issued late on Tuesday.

The tests are part of the agency's first investigation into
claims that toxic chemicals used in hydraulic fracturing are
contaminating ground water.

But officials expressed no views about the source of the
contamination.

"EPA has not reached any conclusions about how constituents
of concern are occurring in domestic wells," the report said.

Concerns about the safety of fracking threaten to slow the
development of vast shale gas reserves that may be sufficient
to meet U.S. natural gas demand for a century or more, experts
believe.

The EPA's latest results were analyzed by federal
toxicologists who recommended that Pavillion residents find
alternative sources of water for drinking and cooking.

For residents whose wells contain organic hydrocarbons, the
new water supplies will be paid for by EnCana, the Canadian
energy company that owns Pavillion's approximately 250 gas
wells, said Richard Mylott, an EPA spokesman.

Some wells were found contain to methane, and their owners
were advised to ensure proper ventilation while showering.

The new samples were collected in January and follow a
less-detailed round of testing in March 2009 during which 11 of
39 wells were found to contain "contaminants of concern."

The latest tests revisited 19 of the 39 initial wells as
well as four irrigation wells, two municipal wells, and some
surface water.

The samples were analyzed for more than 300 substances by
four laboratories, the EPA.

In coming months, scientists will continue testing, and
will focus on possible sources of the contamination, Mylott
said.
(Editing by David Gregorio)