Oil contamination remains a major concern for the gulf.
Officials conceded Thursday it will be a bit longer before they can kill the fractured well that has poured millions of gallons of oil into the Gulf of Mexico.
"We are very very close to the end, this gets to be a very complex evolution," National Incident Commander Admiral Thad Allen told reporters in his daily technical briefing.
That now will include more tests, eventually removing the stacking cap and installing a new blowout preventer.
"Should all these steps prove successful and we move towards the eventual intersection of the well, that could take place sometime the week after Labor Day," Allen said.
As work continues on the floor of the gulf, teams also continue to examine seafood being pulled from the waters.
Government witnesses testified Thursday that after extensive testing none of the seafood pulled from the gulf has shown any contamination.
"We believe fish coming out of Gulf do not have levels of concern," said the Food and Drug Administration's Donald Kraemer.
Meanwhile, federal scientists estimate that only a quarter of the crude that leaked from the fractured well is still there.
A new report from researches at the University of Georgia disputes that claim.
Their study indicates as much as half of the spill may still be there.