State says LANL chromium plume has spread onto San Ildefonso Pueblo land above state limit

LOS ALAMOS - Hexavalent chromium contamination from Los Alamos National Laboratory has spread beyond lab property onto Pueblo de San Ildefonso land at levels above New Mexico's groundwater standard, the New Mexico Environment Department told state legislators.

Santiago Rodriguez, deputy director of the department's Resource Protection Division, presented the findings Aug. 13 to the Legislature's Radioactive and Hazardous Materials Committee, which met at UNM-Los Alamos.

Monitoring Well SIMR-3, in the northern part of the pueblo just south of the lab, measured 98.6 parts per billion in its lower screen in May and 40.1 ppb in its upper screen in June during initial regulatory sampling, according to the department's presentation. Earlier screening samples there showed 72.9 ppb in October 2025 and 90 ppb in March 2026. The state standard is 50 ppb, and the department said the results also exceed the pueblo's own water quality standards.

The lab flushed chromium-contaminated water into Sandia and Mortandad canyons from 1956 to 1972, the presentation says. The department said the SIMR-3 results show the lab's pump-and-treat system, meant to hold the plume inside lab property, has not contained it.

On Feb. 11, two department bureaus served LANL with administrative compliance orders listing violations and penalties. Earlier, in a Nov. 18, 2025, letter, the department's Ground Water Quality Bureau had ordered the U.S. Department of Energy to immediately stop injecting treated water back into the aquifer beneath the pueblo.

According to the department, LANL canceled a series of chromium plume workshops after the orders were served. Pueblo de San Ildefonso, the department, the state Indian Affairs Department, the Office of the State Engineer and Los Alamos County have met in resumed workshops since May, and the department said LANL rejected an invitation to join them.

In a separate action Aug. 5, the department approved Revision 36.1 of the lab's Site Treatment Plan for mixed radioactive and hazardous waste. The revision moves several waste-treatment and shipping deadlines from fall 2026 to fall 2028.