The WV Dept. of Environmental Protection confirmed to Kanawha County Commissioner Kent Carper that the boom heard around Kanawha County was a blast at a mine.
According to the DEP, the blast occurred at Rush Creek mine and was within regulations.
Testing equipment showed that the blast was not excessive.
Tom Aluise, a public information specialist with the West Virginia Department of Environmental Protection, said according to blast logs, contractor Austin Powder set off a mine shot at 5:08 p.m. Tuesday.
"We're not sure exactly why, but at that time, at the site, we're not sure if it's the way they engineered the shot or other conditions associated with the blast that there was larger, more intense than usual air blast," Aluise said.
Additionally, Aluise said the noise was multiplied by weather conditions. The cloudy overcast sky and windy conditions, he said likely increased the area that could hear the blast.
"Those conditions were just right for that air blast to just kind of, usually when there is a blast, a shot set off, the pressure and air blast from the exposure sort of dissipate into the atmosphere," Aluise said. "When there's heavy cloud cover, the air blasts can actually bounce off the clouds and not dissipate into the atmosphere."
No violations of law have been found thus far, though inspectors continue to look into how the blast was engineered. Four of five seismographs in the area had been read so far Aluise said, with the highest reading being 131 decibels, just below the 133 decibel cut-off. He added that numerous complaints prompted the DEP to check out the site.
Spencer Adkins, chief meteorologist at WOWK-13, said there is a phenomenon known as "ducting" of sound waves under the right atmospheric conditions.
"Much like radio listeners may hear a far away station on certain nights when weather conditions are right, sound can travel extremely far distances if conditions are right," Adkins explained. "Basically you need to have what's called an ‘inversion' which is warm air over top of colder air. The sound wave can get sort of trapped in that layer and the sound travels much farther distances within that layer than you would normally expect when standing near the ground."
Adkins said this is the opposite of what people call heat lightning, which is caused when sound waves are dampened to the point they can't be heard when the reach you, even if you saw the lightning.
"You can simply see the flash but can't hear the boom," Adkins said. "This blast brought us exactly the opposite. We didn't see the blast but many people sure heard the boom."