SIMI VALLEY, Calif. -- Lingering radioactive contamination exists at a former rocket test lab outside of Los Angeles that was the site of a partial nuclear meltdown, federal environmental regulators said Wednesday.

The Environmental Protection Agency launched a $42 million study to investigate radioactive pollution at the Santa Susana Field Laboratory, 25 miles northwest of downtown Los Angeles.

Technicians collected 3,735 soil samples from a corner of the 2,850-acre hilltop lab where most of the testing was done. Of those, they found about 10 percent contained radioactive concentrations exceeding background levels.

Most of the contaminated soil was found in places like the materials handling facility that were previously cleaned, but it looked like "isolated spots were missed," said Mary Aycock, an EPA Superfund remedial project manager.

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The pollution occurred in restricted areas of the lab and environmental officials said there was no immediate threat to the community because the site is secure.

The EPA presented its findings at a public meeting in Simi Valley, home of the Santa Susana Field Laboratory. It expects to issue a final report by the end of the month.

The Energy Department conducted nuclear research at the site from the 1950s through 1998. It was the site of 10 reactors, one of which had a partial meltdown, and an open-air pit where workers burned radioactive and chemical waste.

The EPA deals with Superfund sites around the United States and many former Energy Department facilities in the West are more contaminated than Santa Susana, said Michael Montgomery, assistant director of EPA's Superfund division.

The Energy Department, NASA and Boeing Co. are responsible for a cleanup that is being overseen by the state. The deadline for ridding the site of chemical and radioactive pollution is 2017.

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