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The pipeline in my state has leaked multiple times, however fairly minor and never at any of the water crossings. It has also had the most infamous oil tanker disaster, but not nearly the only one.
Most of the pipelines here in the Lower 48 are over 50 years old and have NONE of the safety measures being put into DAPL. Many of them have had spills in the last couple decades.
There's also been many train derailments that have spilled oil as well.
So though I am pro using all energy sources until it's cost effective to go only alternative energy, it'd help if you did some research.
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Their base camp for one is on Indian land and other people who have given them permission to use their land.
And the company building the pipeline are neither perpetrators nor wrong-doers. You protest on public land with a permit, or private land you have permission to be on.
Edit: There's been multiple instances by the protesters since early on that has involved trespass, vandalism or destruction of property.