LOS ALAMOS, N.M. – The EM Los Alamos Field Office (EM-LA) and cleanup contractor Newport News Nuclear BWXT-Los Alamos (N3B) recently achieved full operation of an interim measure to contain and control migration of a contaminant plume in the groundwater.

The groundwater extraction, treatment, and injection system became fully operational after three extraction wells and two injection wells came online this month along the eastern portion of the hexavalent chromium plume. The interim measure now consists of five extraction and five injection wells.

Aside from planned operational pauses and a short suspension due to the COVID-19 pandemic, the interim measure has operated since 2018 along the southern edge of the hexavalent chromium plume beneath Sandia and Mortandad canyons near the boundary between Los Alamos National Laboratory (LANL) and the Pueblo de San Ildefonso.

Operation of the interim measure has brought the hexavalent chromium plume edge about 500 feet away from LANL's boundary with the Pueblo de San Ildefonso. The plume edge is defined by concentrations of the hexavalent chromium below the state standard of 50 parts per billion.

EM-LA Federal Cleanup Director Cheryl Rodriguez detailed the significance of the interim measure, one of several Consent Order campaigns currently underway. The Consent Order is the enforceable agreement between the New Mexico Environment Department (NMED) and DOE for the cleanup of legacy waste that was at LANL before 1999.

“While we have a number of environmental remediation activities underway as part of the Consent Order with NMED, the effort to pull back the plume from the laboratory’s boundary with the Pueblo de San Ildefonso has been our highest Consent Order priority,” Rodriguez said. “We look forward to seeing the impact of the full implementation of the interim measure.”

The system works by pumping chromium-contaminated groundwater from the regional aquifer through extraction wells and piping it to a centrally-located treatment system to remove chromium from the groundwater to achieve chromium levels below permitted regulatory standards. The treated water is then pumped to injection wells along the edge of the plume.

The combined extraction and injection shows the interim measure’s effectiveness at lowering chromium concentrations at monitoring wells. Over time, injection of the treated water lowers the chromium concentrations along the edge of the plume and reduces the plume’s size.

A network of more than 30 monitoring, extraction, and injection wells has been installed in and around the plume, including two monitoring wells that would detect hexavalent chromium before it could reach Los Alamos County’s nearest water-supply well. Installed in 2007, these monitoring wells have never detected elevated concentrations of hexavalent chromium in the groundwater.

Additional monitoring wells will be installed in the northwest and southwest portions of the plume over the next year.

While full implementation of the interim measure is underway, EM-LA and N3B are conducting aquifer and plume characterization to refine modeling that will support development of a final remedy.

From 1956 to 1972, workers at a non-nuclear power plant at LANL periodically flushed chromium-contaminated water from the plant’s cooling towers into Sandia Canyon. At the time, chromium was commonly used as a corrosion inhibitor. The water flowed down Sandia Canyon as surface water penetrated the underlying rock layers, and in time seeped into the regional aquifer beneath Sandia and Mortandad canyons. LANL ceased releasing chromium-contaminated water in 1972.