The bodies of six of nine missing people have been recovered from the site of a chemical tank implosion and rupture in Washington state, officials said Thursday, and efforts were being made to dilute contaminated water.

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The death toll in the incident at a paper mill in Longview on Tuesday is 11, but the remains of three of those people had not yet been recovered by Thursday afternoon.

“Recovery efforts continue,” Longview Fire Chief Brad Hannig said at a news conference. “The priority is ensuring responder safety while treating every victim with the greatest dignity, care and respect.”

Remains recovered from the site are decontaminated before they are sent to the Cowlitz County Coroner’s Office for identification, he said.

The tank that imploded at the Nippon Dynawave plant is designed to hold 900,000 gallons of a hazardous chemical known as white liquor, which is used in the paper-pulping process. It was about 60% full at the time, officials have said.

The implosion occurred around 7:15 a.m. Tuesday as workers were in a shift change, and the six new recovered bodies were found in a workers’ area, Longview Fire Battalion Chief Matt Amos said Thursday.

“It was in an area they would congregate in the mornings, where they would assemble, find out their assignments,” he said.

The tank contained sodium hydroxide, sodium sulfide and disodium carbonate, officials have said.

There is an effort to dilute the high-pH water in ditches that was contaminated with the large amount of chemicals that spilled, officials said.

“A large amount of volume” of material, as well as water used by firefighters, flushed into a ditch across the street from the plant, said Brooks Stanfield, the federal on-scene coordinator for the Environmental Protection Agency.

The ditch sits atop an aquifer and a well field from which Longview gets its drinking water, he said.

“Longview’s water is safe. There is no cause for concerns,” city Public Works Director Chris Collins said Thursday. He said officials were able to divert contaminated water away from a wellhead area.

On Wednesday, officials began a plan to pull fresh water from the Cowlitz River to the east and push the contaminated water farther west and away from the wellhead area, Stanfield said.

That fresh water will dilute the contaminated water and flush it west, and then pumps will pull it to the west and discharge it into the Columbia River, he said.

The water is being monitored to make sure its pH level is lowered to normal levels before it ends up in the river, he said. The latest measurements were below the threshold pH level of 9, he said.

The ditch by the plant is connected to a dike system that runs through the city of Longview, which has a population of around 37,000, Stanfield said.

“We are monitoring those. There are still areas with elevated pH in the water there, and we are continuing to tell people to stay away and to stay out of those ditches and dikes,” he said.

The disaster is likely to be the deadliest industrial accident in modern state history, Gov. Bob Ferguson has said.