|Wetlands coated in oil near Little Rock. Click for photo credit.|
Some pipeline failures such as the Mayflower oil spill in Arkansas, cause local damage and environmental problems. Other pipelines have greater risk. For example, the Tampa area has an ammonia pipeline that leaked when kids broke it (some say to get chemicals for meth). The leak caused the evacuation of a neighborhood and could have killed many.
For a complete list of pipeline leaks and accidents, see this Wikipedia list. It's a bit staggering to see all of the leaks and problems associated with pipelines.