Cal/OSHA to investigate quarry blast

SAN DIEGO - An investigation is set to begin into a quarry explosion that damaged two homes in Tierrasanta.

A Cal/OSHA official told Team 10 that the organization's mining and tunneling unit will start their probe on Monday.

Superior Ready Mix has operated the quarry on Mission Gorge Road since 1991. In a statement, the company said blasting happens three to four times a month.

On Thursday, the company blamed the damage on "an unusual geological condition."

A company statement said a "layer of clay was contained within the rock." In turn, it blew out the side of the wall because of the weaker clay.

The clay flew into a home on Madera Rose Way, creating a bowling ball-sized hole on the side of the house. A window to another home was also broken.

"That soft material didn't need all that energy to break it apart, therefore there was excess energy that sent it flying," said geologist Dr. Pat Abbott.

Abbott said accidents like the one that occurred Thursday are rare, but they can happen.

"I don't think it was carelessness at all," Abbott said. "I think it was something unexpected to them. The easiest thing for them to do is to take in some kind of bulldozer and scrape out that looser kind of material. "

The company said they have not had this type of incident in the 23 years they operated the quarry.

Team 10 called several federal, state and local agencies to search for answers on who regulates the quarry.

The quarry is on city property. However, Superior Ready Mix corporate secretary Arnie Veldkamp said the facility falls under the purview of the Federal Mine Safety and Health Administration.

A spokeswoman with the San Diego County's licensing department said the city of San Diego does issue fines.

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