The underground plume of strontium was detected about seven years ago, Ms. Fallon said.

The underground plume, with peak tritium readings more than 30 times above Federal safe drinking water standards, extends 1.5 miles from the reactor building.

In 2007, public officials and parents expressed concern that the school building sits above an underground plume of toxic waste.

Calls for Dr. Samios's departure began on Jan. 17, when the laboratory announced that the underground plume had been detected.

In 1996, the laboratory announced the discovery of an underground plume of industrial solvents that crept beyond its property.

In 1999 and 2000, Avila was shut down and its beaches dug up to remove an underground plume of oil.

The in situ treatment involves injecting Osorb embedded with reductive metals into underground plumes of contaminated groundwater.

Today, an underground plume of contaminants still lies below more than about 250 acres of the site, though it has been diverted by a treatment system since 1985.

In 1964, a study by the Army Corps of Engineers found the underground toxic plume.

Eventually the underground plume of hydrocarbons reached nearby wells used by residents of the area for drinking water and a cleanup was ordered by state environmental regulators.