(CNN) -- The ruptured Macondo well, a mile under the Gulf of Mexico off the Louisiana coast, has been pronounced dead following the worst oil disaster in U.S. history, but that doesn't mean work associated with the spill is complete, the government's point man for the disaster response said Monday.
"It's going to go on as long as it takes to get the marshes and the beaches clean," retired Adm. Thad Allen told CNN's "American Morning. "We have detailed plans that we've negotiated with the states and the parishes in Louisiana to determine, if you will, how clean is clean."
In some areas, such as Louisiana's Barataria Bay, "we're going to stay with this for quite a while," he said. At some point, officials may decide they have done all they can, "but for right now, we're still at it."
Although authorities say testing does not show high levels of oil remaining in the water, some researchers insist the oil has settled to the sea floor and infiltrated the bottom, where it could affect ecosystems. Asked about those reports, Allen said, "I don't think we can know too much about the Gulf of Mexico and the presence of hydrocarbons in the water column."
He said he has been working with Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration, to develop a long-term subsea oil monitoring program that can be used not only in the response effort, but also as part of long-term restoration.
"What we really need to do is harness all the resources of the federal government and the state and local institutions, including academia, and build a database that can tell us more about the Gulf," he sad. "Right now the readings we're taking don't show large concentrations. We're really talking about microscopic particles of oil. We really need to understand better what's happening on the sea floor."
A joint investigative team is still probing the cause of the explosion on the Deepwater Horizon rig April 20, which killed 11 men and triggered the underwater oil gusher.
Crews last week, as part of the kill process, drilled into the annulus, or the outer ring of the well. No oil was found there, which could be an important clue in the investigation. Allen said it will be up to the joint investigative team, which includes the Department of Interior and others, to determine what occurred.
"There are a lot of theories," he said. "... A lot of people would tell you further down in the well, there was some kind of a crossover between the annulus and the casing pipe where it was cemented. I'm sure we're not going to know that until the investigative team has finished its work."
BP, which owns the well, has left open the possibility of tapping back into the reservoir. Asked whether they should, Allen said that would be a policy decision between BP and the Department of Interior. "Frankly, it's above my pay grade," he said. But he added that any decision would involve "a high level of assurance" by the government.
Asked his personal opinion, Allen said, "I think we've got a lot of problems with energy in this country related to fossil fuels and the need to move to other types of fuels." He called for a "very balanced discussion" taking the risks into account, as well as the need to have an energy policy as the transition is made to more environmentally friendly energy sources.