More workers at a New Mexico nuclear-waste depository will be tested for radioactive exposure after results showed that 13 employees had been contaminated, officials with the U.S. Department of Energy said Thursday. The 13 employees at the Waste Isolation Pilot Plant in the outskirts of Carlsbad were working Feb. 14 when a radiation leak was detected at the facility. The government contractor that runs the plant, Nuclear Waste Partnership LLC, is now asking employees who were present the following day to also submit samples for testing, said Farok Sharif, the company's president. The Energy Department is still in the process of determining the cause of the leak, the first ever reported at the site, which has been storing waste material from the research and production of nuclear weapons deep underground since 1999. But the agency said Wednesday that initial tests show the workers were exposed to americium, a contaminant from nuclear-weapon production. At a news conference Thursday, officials said measurements so far show that radiation levels around the site are below those that would require reporting to the Environmental Protection Agency, but that they are proceeding carefully to ensure the plant can be brought back up safely. Tests conducted by a local research center detected radiation escaped from the facility, but at low levels. "This is still serious for us," said Joe Franco, manager for the Energy Department's Carlsbad field office. "We're going to hold our contractor accountable." The facility, an underground salt mine half a mile below the surface, was created to permanently store items such as contaminated gloves, tools, rags and other trash from sites all over the country. The waste is placed in enclosed metal drums inside rooms carved into the salt formation. Known as WIPP, the site is the only dump of its kind in the U.S. that accepts waste containing concentrations of plutonium and americium above certain thresholds. Plutonium and americium particles can lodge into bones or muscle tissue, affecting cellular structures and DNA, experts say. "When it gets into your body it can do a lot of damage," said Edwin Lyman, a senior scientist at the Union of Concerned Scientists in Washington, D.C. "Even very small amounts are a potential concern." Local elected officials say the information they have received from federal officials so far suggests nearby residents have nothing to worry about. Still, the incident is generating some unease in surrounding communities that have long seen WIPP as a source of high-paying jobs and sponsorships for local sports teams. "Absolutely people are concerned," said Tony Hernandez, a commissioner in Eddy County, where the plant is located. "It's in our backyard."