By Elizabeth Daley
PITTSBURGH (Reuters) - Work will begin next month to extinguish a 10-acre (four-hectare) coal fire that has been burning near Pittsburgh International Airport for years, potentially threatening radar, visibility and a major underground gas pipeline, state officials said on Thursday.
The blaze, which may have started as many as eight years ago, is located just three-quarters of a mile (1.2 km) from a runway, according to John Poister, spokesman for the Pennsylvania Department of Environmental Protection.
"Smoke from the fire has the potential to threaten visibility for air traffic. The fire also poses a risk to a nearby airport radar facility and to a major underground gas pipeline," the department said on its website.
The fire is burning in an underground coal pile left over from mining activities that took place between 1906 and 1939.
"Back in the old days, they didn't mine very efficiently," Poister said, "so there is coal mixed in there in the old mine, but it's not good for anything except smoldering."
He said about 40 such mine fires are burning around the state. The entire city of Centralia was condemned and evacuated due an underground coal fire burning there since 1962. Records from many of the old mines are often not available and they predate environmental regulation, making it difficult to date the fire or its exact cause, Poister said.
"Every now and again you will see smoke wafting up from the ground," Poister said.
Workers plan to dig out the blaze and use several million gallons of water and 200 gallons (750 liters) of firefighting foam.
The $1.5 million project, which is expected to take a year to complete, is subsidized by fees paid by the coal industry on each ton of coal mined in the state.
(Reporting by Elizabeth Daley; Editing by Ellen Wulfhorst and Eric Beech)