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He’s identified only as Controller A in PHMSA’s investigation. He was working console number two—otherwise known as the Montana Crude Pipeline System and Offshore Crude Oil console—at the ExxonMobil Pipeline Company’s operations control center in Houston July 1, 2011. At exactly 10:41 p.m., an alarm notified him that the Edgar Pump Station in Montana had automatically shut down. He pulled up data on pipeline flow rates and pressures, which showed a dramatic drop in suction pressure at the Edgar station. According to PHMSA’s report, the flow rate at Exxon’s refinery in Billings “also dropped from 2,300 barrels per hour to 300.”
The data seemed to indicate a leak in the line. At 10:47, Controller A shut down the pumps. At 10:50, he closed the valve at the Silvertip Pump Station that allows the flow of crude oil into the Silvertip Pipeline. At 10:57, he closed the Laurel valve, located on the north side of the Yellowstone River.
Controller A didn’t notice that the valve station located in Riverside Park had also experienced a drop in line pressure at 10:40. Nine minutes passed between that alarm and Controller A’s shutdown procedure. According to PHMSA, with 2,300 barrels flowing through the line per hour, the estimated discharge at that point would have been 381 barrels.
Controller A turned to a colleague, identified as Controller B, to “check what he was seeing.” At 11 p.m., Controller A contacted his supervisor to alert him of the situation. Seven minutes later, the supervisor instructed Controller A to reopen the Laurel valve and allow the oil in that portion of pipeline to drain into the Billings refinery. By 11:20, the supervisor was on a conference call with additional supervisors and technicians, who PHMSA’s report states felt the low suction alarm could have been triggered by a leak, a faulty transmitter or a number of other factors.
At 11:36 p.m.—56 minutes after the first alarm—Exxon finally closed the pipeline valves upstream of all river crossings. Gravity had been draining the Silvertip of oil for 46 minutes and 12 seconds. PHMSA’s calculations show that roughly 1,444 barrels of oil would have been released during that time; Exxon’s final spill volume was 1,509 barrels.
Exxon got a call at 11:45 that night from the Laurel Fire Department. City officials reported smelling crude oil in the vicinity of Riverside Park. Exxon immediately notified its refinery strike team, which set out for the riverbank around midnight.
Mayor Ken Olson got a call at home around that time informing him of an emergency in the park. He arrived to find the road a zoo—squad cars from the Yellowstone County Sheriff’s Office, Laurel Volunteer Fire Department vehicles, even an ambulance. Response teams put out the order to evacuate residents along the river. “Cenex called out their spill response team, so they were out poking around,” Olson recalls. “We could detect it was an unusual odor.” But with the park flooded with water, no one could get close enough to figure out exactly what had happened.
PHMSA’s investigation concluded that the line failed due to “excessive abnormal stresses” inflicted on the pipe by “bending forces, vibration, and debris accumulation.” The biggest hit Exxon took in the report was a critique of the company’s emergency shutdown procedures. Had those procedures required the controllers in Houston to immediately close the valves both upstream and downstream of the Yellowstone, PHMSA found that “the crude oil release volume would have been much less and the location of the release would have been identified more quickly.”
“The investigative report by PHMSA confirmed the Silvertip pipeline crossing exceeded the federal minimum depth of cover for the installation of a new pipeline in a river,” ExxonMobil Pipeline Company spokesperson Amber Gardner told the Independent by email. “We believe the procedures and training we had in place at the time of the incident complied with federal regulations.”
Buried early in PHMSA’s report is one more indication of the powerful forces at work on the bottom of the Yellowstone in summer 2011. The only other hazardous liquid pipeline at Riverside Park—the one that was purged of crude oil in 2010—also failed that year. “No one knew of this failure because the line remained submerged under the flood water,” PHMSA’s investigation states. “This line failure was discovered after the water receded in September.”