ExxonMobil’s Pegasus Pipeline runs roughly 850 miles between Nederlands, Texas and Patoka, Illinois. It was built in the late 1940s to carry refined oil north from Texas to the Midwest. But in 2006, the flow was reversed and Pegasus became a north-south pipeline transporting unrefined, heavy Canadian crude from the tar sands in western Canada to the refineries in Texas. It was the first time a pipeline designed and built to carry refined oil and petroleum products was re-purposed to handle a very different substance known as diluted bitumen, or dilbit.
The petroleum contained in tar sands occurs in nearly solid form. The consistency has been likened to peanut butter or cold molasses. It cannot be pumped from the ground like conventional crude oil, but must be extracted through mining or a process in which steam forces it to the surface. It is so heavy that, when spilled, it sinks, rendering common methods of oil spill cleanup such as booms less effective. Substantially thicker than conventional crude, it cannot flow through pipelines without being diluted using mixtures of chemical additives and natural gas liquid condensate. It is hot coming out of the ground and stays much warmer than conventional crude throughout the transport process. Dilbit is extracted from sand deposits, and although some separating is performed onsite, it still contains large amounts of abrasive quartz sand particles. It is also acidic, sulfuric and contains heavy metals. This thick, hot, abrasive, toxic product can only be pushed through pipelines under high pressure. According to claimants in one of the lawsuits stemming from the Mayflower, Arkansas spill, ExxonMobil originally considered laying a new pipeline to handle the dilbit, but opted to use the 65 year-old Pegasus pipeline instead.
Re-purposing and reversing flow of existing pipelines are being done with increasing frequency. The Portland Pipeline Company based in Portland, Maine has announced that it is investigating reversing the flow of a pipeline built in 1941 that traverses northern New England and southern Canada to its terminus in Montreal. Instead of carrying refined crude inland from the tanks at Portland, it would now carry diluted bitumen from Montreal to Portland, where it could be loaded on ships bound for Gulf of Mexico oil refineries. The President and Chief Executive of Portland Pipeline stated “All that would happen is that molecules would be flowing in a different direction within the same safe design criteria.” (Boston Globe, April 21, 2013, p.G1). In contrast, according to the Association of Oil Pipelines, pipeline flow can be reversed, but “in most cases requires elaborate and costly reworking.” And as part of its Corrective Action Order to ExxonMobil in the Mayflower spill, the PHMSA noted that while the cause of the rupture is unknown, flow reversal, such as the one in the Pegasus Pipeline in 2006 often results in “hydraulic and stress demands on the pipeline.”
In addition to the highly abrasive nature of dilbit, and the stresses placed on pipeline structure by flow reversal, the third element to be considered by regulators and investigators is the extreme pressure required to propel dilbit through pipelines. In my first piece on the Mayflower spill, I noted that the spill came from a “two to three inch gash” in the line, which is what authorities were reporting at the time. On Monday, April 15, ExxonMobil pulled a 52 foot section of the Pegasus pipeline from the ground. The rupture was 22 feet long, indicating an immense buildup of pressure. The pipe will be examined by an independent laboratory of ExxonMobil’s choosing.
Clean up at the Mayflower site is ongoing. Wildlife has perished, lawsuits have been filed and authorities are nervously monitoring a nearby lake for signs of contamination. The NTSB will not be investigating due to manpower shortages, leaving the PHMSA to monitor the situation.There is no word on when residents will be able to return to their homes.