LOS ALAMOS, Calif. —

A plume of hexavalent chromium, first discovered in 2004, has spread beyond the huge national laboratory's boundaries to groundwater under the Pueblo de San Ildefonso, a New Mexico Environment Department news release said.

Hexavalent chromium, which is toxic and carcinogenic, was periodically flushed with water from Los Alamos National Laboratory cooling towers into Sandia Canyon from 1956 to 1972, when it was stopped.

The U.S. Department of Energy and New Mexico Environmental Department installed wells to monitor the plume and a water treatment system to remove the chemical from the aquifer, but it wasn't completely successful.

However, drinking water on Pueblo San Ildefonso and in Los Alamos County is still potable because the plume is not near private or public

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