As much as 16 percent of the plutonium spilled at the Boulder campus of the National Institute of Standards and Technology in June 2008 may have made its way into the Boulder sewer system, NIST said today in a letter to Boulder’s city manager.

But that amount posed no hazard to the citizens of Boulder, Richard Kayser, NIST’s special assistant for environment, safety and health told Boulder City Manager Jane Brautigam.

“Measurements conducted by a contractor hired by the City of Boulder with funds from NIST detected no radioactivity significantly different from natural background levels at several points within the sewer system, at the wastewater-treatment facility and in the sludge diverted from the the sewer system,” said Kayser.

But he added, “we again acknowledge that this discharge should never have occurred.”

The spill occurred when a project to enhance the United States’ ability to detect “dirty bombs” went awry at NIST, where a subsequent investigation revealed dangerous plutonium sources were obtained without management approval and handled by inexperienced and untrained researchers.

On June 9, 2008, a 30-year-old glass vial containing about 0.25 grams of mixed plutonium isotopes ruptured. A researcher handled the material, significantly spreading contamination in the work area and on his body, a report by the NIST Ionizing Radiation Committee found. He left the area, spreading the contamination outside the lab. The release of plutonium into the sewer system was probably caused by the researcher washing his hands in a sink, according to investigators.

In today’s letter to Brautigam, Kayser said the Nuclear Regulatory Commission-licensed company that cleaned up the lab found that 84 percent of the plutonium involved in the spill was recovered for recycling or removed as waste, “meaning that, at most, 16 percent of the sample may have been discharged to the Boulder sanitary system.”

Kayser said that although the researcher didn’t follow proper procedure when he washed his hands in the laboratory sink, the maximum amount released into the sewer system “fell within allowable regulatory limits.”

The letter informed the city of Boulder that the area contaminated by the spill has now been cleaned and that NIST has met the requirements necessary to reopen the spaces.

Kayser said NIST has taken numerous steps to see that a similar problem doesn’t occur again.

He said NIST is no longer conducting research with radioactive materials under the “specific materials” NRC license. In addition, a senior-level NIST research-director position previously located at NIST headquarters in Gaithersburg, Md., was moved to Boulder to strengthen local line-management responsibility for the safety of all lab activities.

Also, NIST hired a safety manager with extensive government and industry experience to oversee NIST Boulder’s safety office.

Howard Pankratz: 303-954-1939 or hpankratz@denverpost.com