WASHINGTON -- A final Department of Energy report issued Tuesday blamed top Yucca Mountain managers for the scandal in which several scientists appeared to suggest in e-mails that they were making up data and falsifying documents.

Senior management failed to hold workers accountable and to put effective reviews in place to ensure their work met quality assurance standards, the report said.

Fallout from the e-mails that were written between 1998 and 2004 by hydrologists assigned by the U.S. Geological Survey helped tie up the chronically delayed nuclear waste project since they were revealed two years ago this month.

The explosive messages prompted inquiries by Congress, raising questions about Department of Energy management and government science, and giving repository critics clips of ammunition to challenge the proposed Nevada repository.

"Wait till they figure out that nothing I've provided them is QA (quality assurance). If they really want the stuff, they'll have to pay to do it right," stated one message that contributed to the furor.

By Department of Energy estimates, the episode has cost $25.6 million for investigations and do-overs of key computer models.

Sen. Harry Reid, D-Nev., said the report will not put the e-mail controversy to rest.

"Far from it," Reid said. "This report only highlights the fact that senior managers of the Yucca Mountain project were out of touch and failed to do their jobs.

"This is unacceptable when you consider the fact that we are talking about 77,000 tons of the most dangerous substance known to man," Reid said.

"This report is too little, too late," said Rep. Jon Porter, R-Nev., who convened several hearings on the e-mails as a House subcommittee chairman in 2005 and 2006.

An internal department review team focused on 18 e-mails written by the hydrologists and sampled more than 900,000 other e-mails using word searches looking for similar problems.

Reviewers found no evidence that information was falsified as the e-mails suggested, according to the department's review.

Five other suspicious e-mails were uncovered and checked out.

The report did not find that negative attitudes toward quality assurance were widespread among scientists and engineers. But it concluded that top level Yucca officials did a poor job managing for quality.

"The real root cause of the problems came back to the senior management and their unwillingness to hold people accountable to quality assurance requirements, a lack of leadership," said Ward Sproat, who heads the Yucca project as director of the Office of Civilian Radioactive Waste Management.

The findings echoed government audits that warned of persistent weaknesses in quality assurance, an important and meticulous record keeping process that enables research to be validated.

"The GAO must have 20 reports on Yucca Mountain, and almost all talk about management not making a commitment known to the people below them on this issue," said Bob Loux, director of the Nevada Office of Nuclear Projects.

Sproat, a former nuclear industry executive and consultant, took over the Yucca program last year and has embarked on a series of reforms to the project, which is years behind schedule.

In a presentation at the Nuclear Regulatory Commission, Sproat said Yucca Mountain has been marked by top level mishandling of quality assurance since the early 1990s, when the project was taking shape.

"I would not use the word 'indictment,' but I would say that a lot of folks who were in the director's position had not been involved in the nuclear industry and don't understand the importance of quality assurance and how to apply it," Sproat said after his presentation.

Sproat said most of the managers in place when the e-mails were written are no longer with the project, as well as the e-mail authors.

He said no dismissals or reassignments were planned as a result of the new findings.

Sproat said he was meeting with workers to discuss his expectations. He said pay raises for managers would be tied to progress in identifying and fixing mistakes.

Apart from the ongoing corrective actions, the report brings to a close the Energy Department's investigations of the e-mails.

The messages raised suspicions that data may have been manipulated and documents may have been falsified by hydrologists frustrated with the requirements for a computer model they were preparing to project how water flows through the mountain.

"Once more we see the history of mismanagement at Yucca Mountain and an inability on the part of DOE to follow quality assurance procedures, which has been a chronic problem for years," said Rep. Shelley Berkley, D-Nev.