Northwest Pipeline Corporation (Northwest), a Williams Company, operates its 3,900-mile-plus natural gas transmission pipeline system in the northwestern United States. The system consists of a mainline (extending from the San Juan Basin in northwestern New Mexico to the U.S./Canadian border at Sumas, Washington) and numerous laterals that provide natural gas service to customers in six states. The original mainline was constructed in the mid-1950s, when the concern for, and the ability to identify geologic hazards as part of the alignment selection process was much more limited that today. As a result, the pipeline traverses extensive areas with pronounced exposure to numerous potential geologic hazards. A few of these hazards (particularly landsliding) have resulted in significant damage to, or rupture of the pipeline, which has typically been addressed by detailed investigations to characterize and mitigate the specific hazard. Methods have been developed and implemented over more than 15 years to identify and characterize the location, nature and magnitude of the geologic hazards, evaluate their effect(s) on the pipeline, and develop approaches to pipeline operation and management that can be used to mitigate the impacts of the hazards on the pipeline.

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