"That will continue to weather. Mother nature will continue to break it down," she said. "Some of it may come on shore as weathered tar balls, and those will be cleaned up."
Even with the apparent success of the "static kill," BP's job at the site of the collapsed Deepwater Horizon rig is still undone.
Although there was some thought from the company that the mud alone would be enough to plug the well permanently, the federal government has urged it to replace the mud with cement in a "final kill."
"We've pretty much made this well not a threat, but we need to finish this from the bottom," National Incident Cmdr. (retired) Thad Allen told New Orleans' WWL-TV.
BP will pump in cement through the top of the well, and it will also conduct a "bottom kill," pumping cement through the relief wells that are 100 feet from the target, a company spokesman said today.
The cementing process could be complete in as little as two weeks, Browner said.
No matter what, BP executive Kent Wells said Tuesday, "We want to end up with cement in the bottom of the hole."
ABC News' Jeffrey Kofman and Matt Gutman contributed to this story. Additional information from The Associated Press.