Soil and nearby sewers were contaminated by radioactive material from past industrial activities at the site, according to the EPA. "Testing indicates that there is no immediate threat to nearby residents, employees or customers of businesses in the affected area along Irving and Cooper Avenues, " the agency said in a news release.

"Since exposure to the radioactive contamination may pose a threat to health in the long-term, in December 2013, the EPA took action to reduce people’s potential exposure to the radiation and address the potential health risks from the site.

The now-defunct Wolff-Alport Chemical Company operated from 1920 until 1954, processing imported monazite sand and extracting rare earth metals. Monazite contains approximately 6% to 8% thorium, which is radioactive. Radiation can increase a person’s risk of developing cancer such as cancer of the lung or pancreas, according to the EPA

Until 1947, the company disposed of thorium waste in the sewer and on its property. The U.S. Atomic Energy Commission ordered the company to stop those practices in 1947.
More information on the Wolff-Alport site is available here