Lindner said BP wanted to use 400 barrels of the mixture, more than twice the amount of fluid usually used, because the company had hundreds of barrels of the chemicals and wanted to get rid of them.
From the Washington Post:
By first flushing it into the well, the company could take advantage of an exemption in an environmental law that otherwise would have prohibited it from discharging the hazardous waste into the Gulf of Mexico, Lindner said.
Lindner testified that he had concerns, even conducting his own impromptu experiment by mixing small amounts of the chemicals in the hours before the explosion.
He observed a dense grey liquid, similar to the fluid that rained down on the rig the next day -- a fluid the rig engineer described as "snot."