A spokeswoman for the U.S. Occupational Safety and Health Administration said her agency learned about the incident from the news media, and was launching an investigation.
EQT spokeswoman Linda Robertson said that the company's initial findings indicate the victim, a contractor for the company, was at the site to check fluid levels on water storage tanks.
"The safety and security of EQT employees and contractors is a core value and it's a sad day when we lose anyone within our community," Robertson said in a prepared statement. "Our sympathies go out to the families and friends of the deceased."
Pittsburgh-based EQT is one of the largest exploration and production companies in the Appalachian shale-gas field, with drilling rights to more than 3.5 million acres in West Virginia, Pennsylvania, Kentucky and Virginia.
Drillers inject massive volumes of water, sand and chemicals to hydraulically fracture, or frack, the rock in which gas deposits are trapped. The gas then flows up for collection, as does the brine. The DEP says some of the chemicals in the brine could be flammable.
Worker safety is among the growing concerns in northern and north-central West Virginia as a boom in natural gas production continues in the state's Marcellus Shale gas fields.
In June 2010, seven workers were hurt outside of Moundsville when a crew drilling a natural gas well hit a pocket of methane in an abandoned coal mine. And in August 2012, three workers were injured in an explosion at a drilling operation in Harrison County.
DEP said there have been five fatal accidents since 2008. Three have involved well sites, while two involved access road activities.