A government scientist at the center of a controversy over falsifying documents on the Yucca Mountain (search) nuclear dump project received another Energy Department (search) assignment for more work on the project after the problems came to light.

The worker was asked to help run computer models of how water moved through the proposed waste dump site in Nevada -- the same kind of work he was doing when he wrote e-mails about falsifying documents, deleting data and keeping two sets of records, the U.S. Geological Survey (search) said Wednesday.

An Energy Department spokeswoman said late Wednesday that the scientist never billed any hours for the job and that the department has now asked USGS to tell him not to bill for the work. Spokeswoman Anne Womack Kolton said the scientist was hired only to find a file that was needed to make computer models work.

"Essentially a computer file was needed, he was the only person who might know where the file was, therefore they moved forward to authorize him to bill a limited number of hours in order to locate the missing file," Womack Kolton said.

The USGS, where the scientist works as a research hydrologist (search), disclosed the new DOE contract a day after USGS Director Charles Groat assured a congressional committee that workers who wrote and received e-mails about fudging data were no longer working on the project.

USGS spokeswoman A.B. Wade said that after Tuesday's hearing, officials found that the worker identified in congressional documents as "USGS employee 1" was offered a 40-hour assignment with the Energy Department on March 9. The Energy Department learned of the e-mails March 11, and the authorization to hire the worker occurred on March 15, officials said.

On March 16, the Energy Department went public with the news that e-mails written between 1998 and 2000, principally by USGS employee 1, suggested documents had been falsified.

Wade declined to identify the employee, who works for the USGS in California. Criminal investigations by the FBI and the inspectors general at the Energy and Interior departments are under way.

A House Government Reform subcommittee chaired by Rep. Jon Porter, R-Nev., held a hearing Tuesday and released dozens of the e-mails with names and other information blacked out.

In one, USGS employee 1 writes: "I don't have a clue when these programs were installed. So I've made up the dates and names. ... This is as good as its going to get. If they need more proof, I will be happy to make up more stuff, as long as its not a video recording of the software being installed."

The e-mails were circulated among about 10 USGS workers. Wade said two other workers who got the e-mails still are working on the Yucca Project.

The USGS workers involved in the e-mails validated Energy Department conclusions that water seepage through the dump site was relatively slow, so radiation would be less likely to escape.

Yucca Mountain is planned as a national dump to store 77,000 tons of high-level defense and commercial nuclear reactor waste for 10,000 years and beyond in the desert 90 miles northwest of Las Vegas. The project is underfunded and far behind schedule.