The U.S. Army Corps of Engineers is close to finishing its removal of World War II-era radioactive waste from the Mallinckrodt Pharmaceuticals plant in downtown St. Louis.

Uranium, radium and thorium leached into the land around the plant during the 1940s and 50s when Mallinckrodt Chemical Works manufactured uranium to create atomic bombs for the Manhattan Project. The Corps of Engineers has been removing the contaminated soil since 1998.

Six decades ago, the uranium processors simply dumped waste down the drain, said Susan Adams, the project engineer for the clean-up efforts at the site.

“This was all happening before the clean water act was enacted, unfortunately that was normal practice at the time,” Adams said.

The ground then became contaminated through leaky sewer systems and flooding, she said.

Waste from the same project was shipped to north St. Louis County, where it contaminated groundwater and is blamed for cancer in some residents.

Unlike the residential areas there, the downtown St. Louis site is industrial. Mallinckrodt still sits on the site, along with several other industrial companies.

“The majority of our large digs are complete,” Adams said. “We’re now focusing on areas that are harder to reach, take extra engineering controls, more precise digging.”

The cleanup of the downtown property likely will be finished in five years, Adams said. Experts say clean-up efforts in north St. Louis County could take another 20 years.

The radiation is harmful if it’s inhaled or ingested. Just as with the north St. Louis County areas, current workers at the downtown location aren’t at risk of coming into contact with the radiation, since it’s trapped underground, she said.

The Corps of Engineers uses air monitoring systems to make sure it’s dirt-moving projects don’t kick up harmful radiation into the air, she said.

In 2018, the Agency for Toxic Substances and Disease Registry determined that residents who had increased exposure to the contaminated waste near Coldwater Creek in North St. Louis County were at higher risk of certain cancers.

Adams said the Corps of Engineers is only charged with cleaning up the site, not assessing how the radioactive waste affects health.

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