WASHINGTON -- The U.S. attorney's office in Nevada will not pursue criminal charges over allegations that scientists falsified documents at Yucca Mountain, concluding the activities "did not meet the level of criminality," the Energy Department's chief inspector said Tuesday.

Prosecutors indicated they "could not show intent" to commit crimes, said Gregory Friedman, DOE inspector general. The case involved e-mails in which workers expressed disdain for quality assurance procedures on the nuclear waste project.

Evidence focused on e-mails in which hydrologists wrote about making up dates and names, using "fudge factors" and keeping multiple sets of notebooks, one to keep auditors happy and one for themselves.

Friedman said that barring new information, he planned to close his office's investigation on the case, which exploded a year ago in March when the e-mails were revealed.

The messages cast doubt on data that went into computer modeling for water infiltration, an effort that seeks to quantify how much rainfall and runoff might seep into the mountain, where nuclear waste containers would be stored.

The controversy caused DOE to delay the project and spend millions of dollars to double check the research. Managers concluded the science was sound, but they are having the work redone anyway.

Regardless of whether the case is prosecuted, "the actions of those involved -- which have been described by observers as irresponsible and reckless -- have had the effect of undermining public confidence in the quality of the science associated with the Yucca Mountain Project," Friedman said.

He announced the outcome Tuesday in a memo to Energy Secretary Samuel Bodman and in testimony before a U.S. House subcommittee investigating lapses within the Yucca Mountain program.

Three scientists employed by the U.S. Geological Survey were identified as the main authors of the e-mails, which were written between 1998 and 2000.

Inspectors sent their materials to the office of U.S. attorney Daniel Bogden of Nevada in December. Friedman said a decision not to prosecute was made on Monday.

A Bogden spokeswoman said Justice Department rules prohibited him from commenting.

Nevada lawmakers shrugged at the decision not to prosecute the Yucca workers, who were no longer with the project when the e-mails were detailed. The lawmakers said the move should not detract attention from what they called systemic problems within the program that were brought to light by the episode.

"That's a much bigger concern than whether a couple of employees will go to jail," said Sen. Harry Reid, D-Nev.

"Prosecuting the geologists would not have changed one thing," said Rep. Jim Gibbons, R-Nev.

Rep. Shelley Berkley, D-Nev., said the decision "by no means erases the long list of scientific problems still facing Yucca Mountain, nor does it excuse the negligence of those in charge of the project."

Sen. John Ensign, R-Nev., said, "The prospect of criminal prosecutions is secondary to the underlying fact that the science presented by the USGS and the DOE is faulty, misguided and fraudulent."

The pro-Yucca Nuclear Energy Institute "hopes this closes the book on this issue," spokeswoman Trish Conrad said. "The investigations are now over. It is time to move on and move forward."

But beyond the e-mails, Friedman said investigators identified weaknesses in how DOE and its contractors handled the matter.

He said nearly six years passed before the messages were brought to management's attention, though several of them were read by at least one U.S. Geological Survey supervisor and a quality assurance official.

And even after the e-mails were flagged in November 2004 to Bechtel SAIC, the Yucca management contractor, another four months passed before they were brought to the attention of DOE managers, Friedman said.

"We could not find a satisfactory explanation as to why the e-mails had not been recognized as problematic years earlier," Friedman wrote.

He said a DOE report gave as a reason "competing workload priorities and the disruption of work during Bechtel's holiday season shutdown."

Friedman also faulted DOE and the USGS after they learned that a required science notebook had not been maintained. With DOE approval, USGS waived the notebook requirement.

Also, files to support the water infiltration research were lost. Some were found later at the home of a USGS worker.

"If this were NASA and the space shuttle, the space shuttle would not fly," said Rep. Jon Porter, R-Nev., the chairman of the House federal workforce subcommittee that held the hearing to review problems with Yucca Mountain quality controls.

Paul Golan, acting Yucca Mountain director for the past year, said he was working to improve "the quality assurance program and the culture of the organization."

Golan said he has not hesitated to stop work on segments of the project when problems are spotted, and he was working to broaden safety consciousness throughout the Yucca organization.

But DOE continues to face quality assurance problems, said Jim Wells, a director with the Government Accountability Office, which issued a 54-page Yucca Mountain critique last month.

The GAO concluded DOE had a history of undertaking costly repairs to resolve lingering quality assurance problems, while the management tools they were using to track their effectiveness have not worked well.

"They are not out of the woods yet," Wells said, noting DOE is undertaking a repository redesign.