The city of Boulder said Wednesday there is no known risk to the public from plutionium accidentally released into the wastewater system at the National Institutes of Standards and Technology last week.

Traces of plutonium spilled last week at the National Institutes of Standards and Technology in Boulder have been found in a laboratory sink, where the radioactive chemical may have washed into the city's sewer system, NIST said in a news release Tuesday.

The lab was sealed off after a vial of plutonium spilled June 9, but NIST health physicists have since re-entered to conduct an inventory of contamination, according to the release. They found contamination on the floor and tabletops, consistent of the spread of plutonium by hands and shoes.

Contamination also was found in a sink, used by a researcher who worked directly with the plutonium sample to wash his hands after the spill, the release said. Boulder officials were alerted since the sink drains into the municipal sewer system.

The more than 20 employees exposed to the plutonium are being monitored for radiation, but so far none have tested positively, the release said.

It also said NIST has invited the U.S. Department of Energy's Radiological Assistance Program to help assess the contamination and cleanup.

In a press release, city officials said the amount likely released into the city's sanitary sewer system are well below federal and state pollutant limitations for wastewater.

According to the release, water that runs down a drain enters the sanitary sewer system and travels via pipeline to the city's wastewater treatment plant, located east of the city. The wastewater treatment process takes approximately 20 hours to complete. After it's treated, wastewater effluent is released downstream into Boulder Creek. The wastewater treatment process has shown no indication of contamination nor experienced any disruption to the treatment process. Higher flows in Boulder Creek, due to the spring runoff, would have diluted any potential contaminated water even further. The city has seen no indication of impact to aquatic life or the riparian corridor.

Biosolids are created as a byproduct of the wastewater treatment process and are used for land application. City staff will assess any impacts to biosolids produced at the wastewater treatment plant and will ensure it complies with regulatory standards.

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