Residents of Delaware’s western and southwestern communities have grown all too familiar with the booming blasts that occur in the National Lime and Stone Company’s quarry on South Section Line Road. With some concerns having been raised lately by community members regarding the blasts, representatives of the company took part in Monday’s meeting of Delaware City Council to discuss the data surrounding those blasts and to address the community’s concerns.
Chad Doll, who serves as the vice president of corporate relations and development, said it had been “some time” since the company last addressed council on National Lime and Stone’s work in the quarry, and he expressed thanks for the opportunity to do so Monday.
In 2020 alone, the Delaware plant produced 3.7 million tons in its operations. As a whole, the company produced more than 10 million tons last year. Director of Administrative Services Dan Mapes said the Delaware quarry currently has a permit area that spans just under 1,000 acres, with the plan being for the quarry to expand north towards U.S. Route 36 in the years to come.
Blasts, which are done approximately 40 times per year, are conducted at the quarry using a mixture of ammonium nitrate and fuel oil, Mapes said, noting that dynamite hasn’t been used for many decades. Mapes said the mixture is much easier to control in terms of vibrations and air blasts while still giving them the “breakage” necessary.
Four seismographs are set up in the general vicinity of the quarry, around the nearest homes to the blasts, to monitor the vibrations resulting from the blasts. Mapes said the ground vibration limits in Ohio shifted from a one-inch-per-second wavelength to a “Z Curve” to base the limits more on frequency in 2003.
“The lower the frequency of the blast, the more chance there is to, say, crack drywall or put a hairline crack in plaster,” Mapes said. “As you get to higher frequencies, there’s more give there, so to speak.”
The Z Curve shows inch limits ranging from one to two per second, depending on the wavelength of the blast. Drywall and plaster cracks can happen from blasts recording at 0.50 to 0.75 inches per second at certain frequencies, according to Mapes, but all blasts recorded by the seismographs must fall underneath those data points. He went on to say above-grade masonry cracks would require particle velocities north of three inches per second, and concrete or below-grade masonry would require velocities higher than five inches per second, well above what is being recorded at the quarry.
During the presentation, Mapes showed seismic reports from blasts conducted on March 30, which show all data points being recorded well below the curve used to determine risks to nearby structures. Naturally, for the seismographs furthest away from the blast site, the data points dropped significantly below the limits.
As for houses that have a wooden frame, Mapes referenced a study conducted by the United States Department of the Interior that concluded it would take two blasts daily that generated 0.5 inches per second in ground motions for a duration of 28 years before the first crack to show in a wood foundation.
Asked by City Manager Tom Homan about how long National Lime and Stone anticipates operations to continue at the Delaware quarry, Mapes offered a time frame of 50-100 years. “There are usable reserves below where we’re mining now, as well, so it’s not just that surface,” Mapes said.
Some residents have inquired about a notification system that would alert them to pending blasts. Mapes said in the past, a whistle would be blown, but found the whistle served as a call for the curious who were interested in trying to get a look at the blasts. Doll said it would be difficult to imagine being able to notify mass groups in the community of when a blast is going to happen, given the many factors that make a blast time fluid. However, Doll said he would be interested in discussing possibilities with the city. Mapes added there is an extensive list of people already who are notified prior to the blasts via a text message.
National Lime and Stone’s entire presentation to council can be viewed by visiting the city’s Facebook page and accessing the stream from Monday’s meeting.