There is more evidence of questionable work on the Yucca Mountain nuclear waste dump in Nevada, an Energy Department inspector general's report said Wednesday.

Criminal investigations already were underway into a batch of e-mails the Energy Department disclosed in March that suggest government scientists falsified data on the project.

The inspector general uncovered more e-mails that raise new questions about work on the project.

"The office of inspector general found e-mails by other authors that identified possible conditions adverse to quality at Yucca," the report said. "However, these e-mails had not been identified by Yucca personnel as requiring further review."

One e-mail cited by the report says that the office of quality assurance "just discovered that (quality assurance) software requirements were being ignored." Another says: "We may want to backdate the notebook to when we started putting things together."

The report doesn't say who wrote the e-mails or how many were found, and a spokeswoman for the inspector general said she couldn't elaborate because of the criminal investigation into the original e-mails. Those were written by U.S. Geological Survey scientists studying how water moved through the dump site in the desert 90 miles northwest of Las Vegas.

It's not clear whether the newly discovered e-mails dealt with the same issue.

The report also says Yucca Mountain workers have not adequately focused on quality control in their reviews of e-mails written in connection with the project, and they should go back and look at approximately 10 million project e-mails. The e-mails and other documents are being reviewed as the Energy Department readies an application for a Nuclear Regulatory Commission license to operate the dump.

Craig Stevens, a spokesman for the Energy Department, said department managers have signed off on a corrective action plan to implement the report's recommendations. He said the 10 million e-mails -- plus an additional 4 million subsequently discovered -- will be reviewed through statistical sampling

"We certainly appreciate the information the inspector general gave and the recommendations the inspector general presented and this is something we take very seriously," Stevens said.

Problems at the Yucca Mountain dump, including the e-mail controversy, have delayed the projected opening date by years and it's now not expected until after 2012. The dump was approved by Congress in 2002 as a national repository for 77,000 tons of spent reactor fuel and high-level defense nuclear waste. It faces strong opposition from Nevada lawmakers.