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“Severe environmental impact”
Several weeks after the August 2010 meeting in Riverside Park, city officials in Laurel contacted the federal Pipeline and Hazardous Materials Safety Administration with concerns that future flood events could undermine the integrity of the pipelines under the Yellowstone. PHMSA promptly contacted the appropriate companies, focusing specifically on ExxonMobil—given that the other pipelines were either laid up or transporting natural gas. According to PHMSA’s new investigation report, the agency believed at the time that a failure in Exxon’s Silvertip line “would cause severe environmental impact.” Exxon responded by conducting a depth-of-cover survey of its pipeline crossing at Riverside Park. The company submitted its findings to PHMSA on Jan. 19, 2011, showing that the pipe was a minimum of 5.3 feet below the riverbed, or 1.3 feet more than the minimum federal requirement. Furthermore, Exxon claimed the bottom of the river hadn’t changed significantly since the company had conducted its last survey.
That survey occurred in 2002.
PHMSA cautioned Exxon that it should maintain vigilance in monitoring the Silvertip. But by spring 2011, Exxon’s new depth-of-cover data had put most concerns about the riverbed at ease. Attention shifted to the erosion along the south bank at Riverside, which PHMSA notes “was extensive and was continuing.” Heavy rains were causing the Yellowstone and other rivers in the state to swell quickly. On May 25, city officials in Laurel again emailed PHMSA with concerns about the impacts of seasonal flooding. Exxon shut down the Silvertip for five hours and assessed the site, but decided that daily drive-by checks would be adequate to gauge the state of the river.
Over the next few days, PHMSA started monitoring all pipeline sites across the state in response to rising flow rates. The agency contacted all of the major pipeline operators in an attempt to gather information on any potential problems. Floodwaters had begun to recede, but warmer temperatures were imminent. Snowpack to the west would be melting soon.
The primary concern for Laurel throughout the spring and early summer wasn’t necessarily the crossings under the Yellowstone itself. Officials were far more worried about the flood washing over the bank at Riverside Park and threatening the unprotected sections of pipeline there. On June 24, Exxon shut down the Silvertip a second time. Snowmelt had caused the river level to rise again, but Exxon resumed the flow of oil the same day after conducting another site visit. The company placed sand bags around its remote-controlled valve station in Riverside June 25 to protect to the facility. According to PHMSA’s investigation, “Exxon personnel state that they had no indications that the pipeline crossing in the river was exposed.”
PHMSA did conclude that Exxon “took reasonable precautions to address the flooding of the Yellowstone River in the spring and early summer of 2011.” The report goes on to state that the company “may not have known that the river bottom could change sufficiently to undermine their pipeline.” Laurel’s concerns in Riverside Park were gradually refined in spring 2011 to the erosion of the south bank and the continued safety of the park itself. But that fear clearly implies floodwaters were radically changing the river immediately downstream of the Highway 212 bridge.
Of the four pipelines running under the Yellowstone in the Laurel area, two transport natural gas—a substance that, if released, inflicts little immediate damage to the surrounding environment. A third, which at one time transported crude oil, had been purged with nitrogen and retired in early 2010.
The fourth pipeline, ExxonMobil’s Silvertip, was the only active crude oil line at Riverside Park in summer 2011.