Environmental and tribal groups protesting an oil pipeline from North Dakota said in a letter to the White House it poses a threat to their existence. Tribal groups are suing federal regulators over permits for the 1,134-mile pipeline because of threats to the Missouri River and other regional water ways. The U.S. Army Corps of Engineers, which examined separately each water crossing, is accused of sidelining tribal interest. In a letter to President Obama , tribal and environmental groups said the oil pipeline from North Dakota would threaten sacred sites and potentially parts of the regional drinking water supply. “If there were to be a spill, which history has taught us is not a question of if […]