The U.S. Environmental Protection Agency (EPA) found benzene and methane in wells and in groundwater in Pavillion, Wyoming, agency officials said in a report.

At a community meeting with well owners, EPA officials revealed Tuesday they found low levels of petroleum compounds in 17 of 19 drinking water wells sampled, and that nearby shallow groundwater was contaminated with high levels of petroleum compounds, such as benzene.

The affected well owners were advised not to drink the contaminated water.

At this point, the EPA has not reached any conclusions about the sources of the chemical compounds found in drinking water wells, including hydraulic fracturing or “fracking,” the controversial process used to extract natural gas from underground sources.