Exxon Mobil on Sunday continued cleanup of a pipeline spill that spewed thousands of barrels of heavy Canadian crude in Arkansas as opponents of oil sands development latched on to the incident to attack plans to build the Keystone XL line. Exxon spokesman Alan Jeffers said on Sunday that crews had yet to excavate the area around the pipeline breach, a needed step before the company can estimate how long repairs will take and when the line might restart.