BP shot a load of toxic chemicals into the Deepwater Horizon well to get around waste disposal laws, but it's not something they've ever done before. From the article:
"The reason for the action: BP had hundreds of barrels of the two chemicals on hand and needed to dispose of it, Lindner testified. By first flushing it into the well, the company could take advantage of an exemption in an environmental law that otherwise would have prohibited the discharge of the hazardous waste into the gulf, he said."
Small leaks spring at BP oil well; cap to stay in place for now