Two men died in an accident at a wastewater treatment plant in Texas on Oct. 22, the Beaumont News reported.

The men had been performing repairs at the Roberto R. Bustamante Wastewater Treatment Plant in El Paso when a surge of sludge filled the equipment room where they were working.

“When a leak occurred in the pump pit, it began filling with water. One of the workers went into the pit to attempt to close a valve, but was not able to remove himself from the pit. Another worker entered the pit and also was unable to escape,” explained Diana Petterson, a spokeswoman for the U.S. Department of Labor, quoted by KFOX14.

The El Paso Fire Department was initially called out to rescue two people, but when fire officials arrived at the scene it turned into a recovery effort as both men had died. The accident is now being investigated by the Occupational Safety and Health Administration, which by law has six months to report on what went wrong.

The two men were employed by Cubic Water LLC, and were contracted by the city of El Paso.

John Balliew, president and CEO of El Paso Water Utilities, said in a statement: “We would like to express our most sincere condolences to the families of the two victims of this accident.”

The plant will operate at a reduced capacity until repair work is completed.