The waste is called "mixed waste" because it contains hazardous substances or metals as well as low-level radioactive materials.

The Aug. 27 order from T.H. Murphy, the division's Federal Facilities Bureau chief, to Stephen Mellington, the NNSA's assistant environmental manger, says, "We believe that the corrective actions taken to date may not be sufficient to fully correct the underlying waste characterization problems. It is also noted that the time to correct problems or initiate corrective action has taken longer than is considered acceptable."

One truck shipment from the Portsmouth Gaseous Diffusion Plant in Piketon, Ohio, arrived for disposal at the test site with a leaking container in March. Kevin Rohrer, an NNSA spokesman in North Las Vegas, said, "At no time was public health or safety in danger."

Rohrer said the truck's driver noticed water leaking from a cargo container on the back of his flatbed truck March 5 as he drove north on Interstate 15.

"He pulled over at the closed inspection station on Interstate 15, near the Sloan exit" and contacted the Nevada Highway Patrol and the Environmental Protection Agency, which sent investigators, Rohrer said in an e-mail.

Rainwater, he said, had dripped down through a hole in the roof of the container. The water was surveyed and determined to be free of contamination, and the shipment was cleared to continue for disposal at the test site, 65 miles northwest of Las Vegas.

NNSA sent a request for corrective action to the Portsmouth plant, and the leaking container was set aside after it arrived at the test site. On Aug. 1, test site officials found that the container held lead and cadmium and that the waste had not been characterized properly. The container was sent back to Portsmouth on Aug. 27.

Officials from the test site and the Nevada Division of Environmental Protection are traveling to Portsmouth this week to observe the waste being sampled for positive identification.

The other two alleged permit violations involved wastes shipped by Foster Wheeler Environmental Corp., and M&EC Perma-Fix Environmental Services, according to the division's Aug. 27 cease order.