The trans-Alaska oil pipeline shut down Tuesday after as much as several thousand barrels of oil overflowed a storage tank into a containment area at Pump Station 9 near Delta Junction, state and pipeline officials said.
The tank continued to leak oil Tuesday night at a rate of about five gallons per minute but the oil was not threatening to escape the containment area, which can hold millions of gallons, officials said.
The state Department of Environmental Conservation is investigating the spill. DEC on-site coordinator Tom DeRuyter said the priority is making sure the site is safe before the pipeline is restarted and before workers begin cleaning up the oil. The concerns are toxic fumes and potential fire, he said.
"You don't want to bring power in that could act as a combustion source," he said.
A spill of several thousand barrels would be one of the largest ever for the 33-year-old pipeline. A barrel is 42 gallons.
Pipeline officials said they do not know when the pipeline will be operating again. "We will not start back up until we are absolutely comfortable that it's safe," said Michele Egan, spokeswoman for Alyeska Pipeline Service Co., the oil company consortium that runs the pipeline. "We are taking a very measured approach to making sure the site is secure."
No one was injured in the incident, and the site has been evacuated while Alyeska officials analyze the scene.
"We are taking the most conservative approach we can," Egan said. "The crude oil is contained now. It can stay in that containment area without impacting the environment around it."
Additional spill response teams were en route to the pump station, she and state officials said.
The spill occurred Tuesday morning during a planned six-hour shutdown of the pipeline and testing of its fire-command system, Egan said. The spill wasn't from the pipeline itself but from a tank attached to the pipeline that catches overflow when pipeline valves are opened to relieve pressure, Egan said.
As crews were testing the fire system, the power failed and the valves that are normally closed on the tank opened, which is what they are designed to do when the power is interrupted, Egan said. The system reacts to protect the line from too much pressure.
The valves were open for an hour, Egan said.
Alyeska is investigating whether there was operator error in addition to mechanical error.
The oil that overflowed from the tank's vents at the top spilled into the larger 105,000-barrel containment area bordered by berms. In photos of the scene, the oil does not cover the entire ground of the containment area.
The overflow area is lined with an impermeable fabric, the DEC said.
Egan said that while the pipeline is shut down, North Slope oil producers have scaled back production to 16 percent of normal. The oil can be stored temporarily in large tanks near Pump Station 1, just south of Prudhoe Bay, she said. Alyeska has enough room in those tanks to store oil at the reduced rate for 48 hours, Egan said. "It buys us some time," she said.
"We said right away, look, let's give ourself the room so that we can do this in the best possible way because the first priority is the safety of the people and of the facility, the commercial issue comes later."
About 40 workers were evacuated when the pump station was closed, Egan said. Ten stayed in the area for essential operations.
The station is about a mile from the Richardson Highway. The access road has also been closed, Egan said.
Thunderstorms were forecast overnight, DeRuyter said. If it rains, that will increase the volume of the liquids that have to be removed. "I don't see that as a major problem," he said. "I don't know if lightning is going to pose a safety threat, but they definitely will be keeping their eye on that."
The 800-mile pipeline in April carried about 650,000 barrels per day from the North Slope to Valdez.
The pipeline from Prudhoe Bay to Valdez was finished in 1977 and began operating with 11 pump stations, but today only four are used to move the oil -- stations 1, 3, 4 and 9. Where the spill occurred is the last pump station before Valdez.
It's not unusual for the pipeline to shut down for short periods of time, Egan said. Almost quarterly, Alyeska halts flow for routine maintenance and testing, sometimes for as long as 72 hours, she said.
Alyeska and the pipeline are owned by BP (46.9 percent), Conoco Phillips (28.3 percent), Exxon Mobil (20.3 percent), Koch Industries (3.1 percent) and Chevron (1.4 percent).
Alyeska will try to salvage the spilled oil by pumping it into a truck, filtering it if it needs it, and putting it back in the pipeline, Egan said.
This isn't the first time that Pump Station 9 has had a serious incident involving the same storage tank. In January 2007, a portable space heater ignited crude oil vapors that had escaped into the tank's containment area while Alyeska was running tests and doing maintenance at the pump station, according to federal records.
Federal pipeline regulators cited Alyeska for having the heater too close to the tank, for not reporting the fire in a timely manner and for relying on "grossly deficient" work procedures. The regulators proposed a $817,000 fine against Alyeska for the fire and two other pipeline safety violations that happened within two months of the fire. However, Alyeska contested the fine and federal records show that the case is still open.
Nobody was injured in the fire.