Natural gas is no longer leaking from the base of a storage tank at the 80-acre Plymouth facility rocked by an explosion earlier this week, officials said Wednesday.
Crews managed to shut off a valve that helps control the flow of gas, said Michele Swaner, spokeswoman for Williams Partners, the subsidiary that owns the plant.
Safety concerns about the gas and vapors slowly leaking from the tank following Monday's explosion prevented crews from shutting off the valve, Swaner said.
"Above all, there are safety (concerns) you must consider," she said. "It just takes time to get in and turn the valve off."
Shrapnel from the explosion punctured holes at the base and near the top of the tank, officials said. Several buildings at the facility were also damaged, including a control room, a compression station and a mechanic shop.
Nontoxic vapors continue to seep out near the top of the tank, Swaner said. But the vapors are not harmful and dissipate in the air. Crews are working to stop those leaks too.
The main focus of Williams Partners is making sure the plant is safe, Swaner said.
"Essentially (crews) are on site to continue to secure and evaluate the operation," Swaner said. "It really is going to take time to find out what happened and assess the damage. We will work with regulatory (agencies) and subject matter experts will go on site to help determine what happened."
Williams Partners does not know how much natural gas has been lost or how much remains in the damaged tank, Swaner said. The tank was about one-third full with an estimated 7 million gallons of natural gas inside.
It's unclear if the damaged tank will need to be replaced, Swaner said. Piping and yard valves were also damaged.
State and federal agencies will join together to investigate the incident in the rural community of about 300 people in south Benton County.
Officials from the Utilities and Transportation Commission, the Department of Labor & Industries, and the U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration are involved.
Detectives with the Benton County Sheriff's Office are also assisting in the investigation to determine if any crimes were committed, said Deputy Joe Lusignan. There is no evidence of foul play.
Residents were allowed to return to their homes Tuesday after an evacuation order was lifted.
Local officials warned residents about perlite, a dustlike substance, that was released in the air around Plymouth. Perlite can cause irritation and shouldn't be inhaled. It's used to insulate the tanks.
Williams Partners plans to conduct air quality studies to determine how much of the substance is in the air, Swaner said.
Swaner confirmed all five people injured during the incident were employees of the plant.
One man still remains in a Portland hospital with burns to his face and hands, she said.
Williams Partners was impressed by the response of local emergency personnel and thankful of their help over the past few days, Swaner said.
"They were great. I thought they did an outstanding job," she said.