Oil spills on Alaska's North Slope have raised environmental hackles, days before a Congressional vote on the Bush administration's plan to open the nation's arctic refuge to oil drilling. The incidents, which include last week's 420-gallon (10-barrel) oil spill from a pipeline in Prudhoe Bay - a field that sprawls over roughly 400 square miles (1,036.000 sq km) of tundra - have drawn concern that even routine oil operations in the Arctic National Wildlife Refuge (ANWR) would cause lasting environmental damage.