(CNN) -- The beginning of the end could be little more than a week away for the capped, sunken oil well in the Gulf of Mexico -- that is, if the latest timeline for permanently killing the ruptured well holds up.
Retired Coast Guard Adm. Thad Allen, the head of the government's oil spill response, said Friday that BP tentatively expects to intercept the ruptured well through the closer of two relief wells around August 14 or 15.
While the "static kill" that involved pumping mud and cement into the upper part the pipe earlier in the week could potentially plug the well for good, Allen has instructed BP to proceed with a final "bottom kill." That's when more mud and cement will be poured into the well through one of two relief wells. The bottom kill amounts to an insurance policy.
Doug Suttles, BP's point man on the oil-disaster response, said on Friday crews are moving forward with plans to complete the first relief well and perform the bottom kill. They will determine whether the cement pumped into the top of the well has hardened enough.
As the cement hardened Friday in the crippled well, Allen said preparations for more drilling on the first Gulf of Mexico relief well continued. Between Monday and next Friday, crews expect to alternate drilling with ranging runs, which use an electronic current to gauge locations thousands of feet deep, he said. Drilling on the second relief well, which was created as a redundant measure, is on hold.
BP finished pouring cement down the well on Thursday as part of the "static kill," completing the job earlier than expected. The process took six hours.
The cement was poured on top of 2,300 barrels of heavy drilling mud sent down from a ship on the surface Tuesday, pushing oil back into the well reservoir.
Before word came that the cementing had been completed, retired Coast Guard Adm. Thad Allen said the development would amount to a "significant milestone" in the long-running fight against the BP oil spill. Allen is the federal point man in the oil spill effort.
He said the cementing phase of the "static kill" operation is not the end of the process, "but it will virtually assure us there's no chance of oil leaking into the environment."
"I think we can all breathe a little easier regarding the potential [that] we'll have oil in the Gulf ever again," Allen said Thursday. "But, we need to assure the people of the Gulf and the people of the United States that this thing is properly finished and that will be through the bottom."
Friday marks the 109th day since the environmental disaster started with the explosion on the Deepwater Horizon that sank the rig and killed 11 workers.
Oil flowed relentlessly for nearly three months, as BP tried various methods to cap the runaway well, until it finally placed a tightly fitting cap on it in mid-July. That opened the door for the efforts now under way to permanently seal it.
Despite the optimistic notes being sounded about killing the well, the long-term cleanup is another matter.
The federal government's on-scene coordinator, Rear. Adm. Paul Zukunft, said Thursday it's possible that tar balls may be washing ashore for years.
A government report released this week concluded that of the nearly 5 million barrels of crude oil that spilled into the Gulf when the well was out of control, roughly a quarter of it remains in the water either on or just below the surface as a light sheen and weathered tar balls.
The rest has been collected by skimming ships, burned on the surface, broken up by dispersants or evaporated.
The tar balls are either washing ashore, being collected from the coastlines, or buried in sand and sediment, and are in the process of being degraded, the report said.