The Trans-Alaska Pipeline was engineered to accommodate the highly varied terrain and considerable level of seismic activity experienced in the region. Because the pipeline would run directly through the heart of untouched wilderness and face scrutiny from both Alaska Native and environmental groups, the pipeline was also designed with environmental safety in mind. Perhaps not surprisingly, these groups and oil industry representatives differ in their assessment of the pipeline's performance to date.

While protecting Alaska's ecology was of utmost importance to critics of the pipeline, many of the engineering solutions appear to have proven to be sound up to this point. At the source in Prudhoe Bay, oil lies several thousand feet below ground. When it arrives at the surface, it can be as hot as 180° Fahrenheit. At this temperature, oil in the pipe would thaw a cylindrical area 20 to 30 feet in diameter in the frozen soil within a decade. To address this, engineers installed heat exchangers to cool the oil to about 120° before it entered the pipeline, and further protected the ground by elevating more than half the pipeline's 800-mile length. The pipeline's structural design allows for the pipeline to flex in the event of an earthquake. In November of 2002, when the Denali Fault in central Alaska experienced a magnitude 7.9 earthquake, the ground slipped 18 feet laterally and more than 3 feet vertically beneath the pipeline, yet not a single drop of oil was spilled.

With respect to protecting wildlife, Alaska Native peoples and conservationists believed the pipeline would disrupt land-animal migration routes. Engineers were therefore pressed to allow crossings in many designated areas. Reports conflict as to how well caribou have fared. While oil industry representatives note a doubling in caribou populations overall, wildlife biologists attribute this to other factors. Some Iñupiat residents living in communities adjacent to oil pipelines and maintenance roads are convinced that caribou migration patterns have changed. They attribute this to the noise, lights, pipelines, and roads in and around the oil pumping facilities and along the pipeline routes.

Oil industry executives contend that the pipeline is among the world's cleanest. Safety provisions include special valves that can shut down flow in the event of a leak within minutes of detection. Conservationists suggest that, despite these provisions, at least one spill a day occurs. Because oil passing through the pipeline contains water, which can corrode the pipes, monitoring and replacing corroded pipe will be a major issue as the pipeline ages.

The worst oil contamination incident related to the pipeline did not occur along the pipeline but in the marine environment. In 1989, the Exxon Valdez spilled 11 million gallons of crude oil into Prince William Sound. It was the worst oil spill in U.S. history, with fallout to the ecosystem, local economy, and subsistence ways of life still being felt today.

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