BP backed down Thursday from its plans to dump more pollution into Lake Michigan, but critics want the oil giant to ensure its promises are legally binding. Responding to a month of unrelenting criticism from politicians and the public, BP pledged it will not invoke provisions of a new permit that allows the largest oil refinery in the Midwest to release significantly more ammonia and suspended solids into the lake...The decision is a victory for opponents who argued the permit undercut decades of efforts to clean up Lake Michigan...the source of drinking water for Chicago and scores of other communities.