The U.S. Army Corps of Engineers has completed testing inside a Missouri school closed amid concerns of radioactive contamination, and sampling of soil outside the school has begun, Corps officials said Friday.

A suburban St. Louis school board voted last week to close Jana Elementary School in Florissant, Missouri, after testing by a private firm found levels of radioactive isotope lead-210 that were 22 times the expected level on the kindergarten playground. It also found high levels of polonium, radium and other material inside the school, which sits along Coldwater Creek, a 19-mile (31-kilometer) waterway contaminated decades ago with Manhattan Project atomic waste.

The Corps said in a news release that radiation detection instruments were used to scan surfaces inside the school. That work began Monday and concluded on Friday.

Sampling of soil outside the school began Wednesday and is expected to go on for another two weeks, the Corps said. The agency plans to sample at least 45 spots, with depths ranging from 15 to 28 feet below the surface.

Preliminary test results are expected in November.

“Public safety is our top priority,” Col. Kevin Golinghorst, St. Louis District commander, said in the release. “Our team has the right expertise and experience to complete this work.”

The approximate 400 students at Jana Elementary are taking virtual classes for the next month, then will be reassigned to other schools. It hasn’t been determined when Jana Elementary will reopen.

Coldwater Creek was contaminated in the 1940s and 1950s when waste from atomic bomb material manufactured in St. Louis got into the waterway near Lambert Airport, where the waste was stored. The result was an environmental nightmare that resulted in a Superfund declaration in 1989.

The site near the airport has largely been cleaned up but remediation of the creek itself won’t be finished for another 16 years, Corps officials said.

A 2019 federal report determined that those exposed to the creek from the 1960s to the 1990s may have an increased risk of bone cancer, lung cancer and leukemia. Environmentalists and area residents have cited several instances of extremely rare cancers that have sickened and killed people.

The Corps of Engineers earlier found contamination in a wooded area near the school, but hadn’t previously tested the school or its grounds. This summer, lawyers involved in a class-action lawsuit representing local residents seeking compensation for illnesses and deaths received permission from the Hazelwood School District to perform testing.

Results from testing done by Boston Chemical Data Corp. were released earlier this month, prompting the decision to shut down the school.

It’s unclear exactly what any cleanup would involve, how long it would take or who would pay for it. A school district spokeswoman declined comment.