That amount of cement dust, which blanketed a nearby residential neighborhood, is the equivalent of 160 50-pound bags of cement.
The Martin Marietta plant filed an air emission event report about the July 19 incident with the Texas Commission on Environmental Quality. That agency regulates particulate matter for the plant located along SH 5.
According to the Aug. 2 report, the cement dust was released between 1:30 a.m. and 6:45 a.m. after "an automatic shutdown system for one of the cement silos at the McKinney plant failed to operate correctly to shut down a blower motor. The result was that the system continued to fill a silo with cement beyond the capacity of the silo."
The report stated that a pressure release valve activated, causing the cement dust to be released. No one was working at the plant at the time, so the release continued until the system was manually shut off, according to the report.
A separate report from the city of McKinney said the fire department was dispatched at 11:39 p.m. on July 18 to one of the facilities on SH 5.
"No fire was found but [the fire department] observed a cloud of dirt and dust being emitted from some equipment on site," according to the city's report.
Amanda Miller, director of Government Affairs and Public Relations for Martin Marietta, said the dust event began at 8:17 p.m. on July 18. The system was was shut off approximately five hours later, around 1:30 a.m. on July 19, after an employee driving by saw the dust coming from the silo.
Operations at Martin Marietta's McKinney plant ceased July 19 and remains closed as of Aug. 9.
"The plant will not be operated again until it is tested by a third party and shown to be operating correctly in terms of all of its systems and in compliance with its permit," according to the report.
Much of the concrete dust fell on the McKinney Greens neighborhood located across the highway from the plant. Dust and noise from Martin Marietta and two other industrial plants along SH 5 have been a concern for residents in the area for years. But never before has it been this bad, residents say.
“We’ve never been impacted with an episode that has tracked like this,” McKinney Greens resident Dotti Stevens said in a previous interview with Community Impact Newspaper.
After the cement dust release, the plant sent crews to help clean up homes, cars and other affected areas in the neighborhood. According to an email from the TCEQ, no long-term concerns are expected once the dust is removed.
As of Aug. 8, Martin Marietta has worked with 138 residents to clean their property, said Miller. Cleanup efforts include interior, exterior, street, swimming pool and duct cleaning services, in addition to car wash services.
Cleanup efforts will continue and property owners seeking assistance with cleanup should contact Martin Marietta at 972-647-3300 or firstname.lastname@example.org, according to the city of McKinney.
Editor's note: Additional information has been added to this article.