
NGOs Apply for Appropriations Funding to Protect Communities from LANL’s Migrating Hexavalent Chromium Plume
On November 18th, 2025, the New Mexico Environment Department withdrew its
temporary authorization to the U.S. Department of Energy and ordered it to cease the
injection of “treated” groundwater back into the regional sole source drinking water
aquifer. Elevated levels of hexavalent chromium above regulatory standards had been
detected for the first time in the deep regional drinking water aquifer beneath Pueblo de
San Ildefonso. It had migrated through the complex geology of the Pajarito Plateau,
where Los Alamos National Laboratory (LANL) is located, to deep groundwater below
the Pueblo’s lands. The discovery was made during the drilling of a new monitoring well,
known as SIMR-3, or San Ildefonso Mortandad Regional – 3, located just south of the
boundary between LANL and the Pueblo.
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