Chromium from TA-5

Groundwater sampling data from monitoring wells at LANL indicate the presence of chromium-6 contamination resulting from historical discharge of wastewater from Technical Area 3 (TA-3), which was active from 1956 until 1972 (N3B Los Alamos, 2019). A non-nuclear power plant with cooling towers located in TA-3 was the source of the contamination. The pipes of the cooling towers were coated with a corrosion-inhibiting and anti-rusting chemical called potassium dichromate, which dissociates to produce chromium-6 (Katzman, 2017). Workers periodically released chromium-contaminated wastewater from these towers into the head of Sandia Canyon (NukeWatch, 2017). About ninety percent of the chromium-6 converted to non-toxic chromium-3, while the remaining chromium-6 (estimated to be at least 2,000 kg) traveled down Sandia Canyon via surface water and seeped through the underlying rock layers into the regional aquifer below Mortandad Canyon to become the existing plume (Chamberlain, 2019; N3B Los Alamos, 2019). The figure below displays the pathway of the wastewater from the source to the aquifer.

In December 2005, LANL reported to the NMED that there was a chromium plume located 900-1,000 feet below the canyon bottom and within the top 100 feet of the aquifer (Katzman, 2017; N3B Los Alamos 2019). It measured approximately 1 mile long by 0.5 miles wide by 50 feet in depth (Katzman, 2017). Plume concentrations exceeded the New Mexico groundwater standard of 50 parts per billion (ppb) and the EPA’s drinking water limit of 100 ppb and reached levels as high as 1,240 ppb in the center (DOE Environmental Management Los Alamos Field Office, 2015; Agency for Toxic Substances and Disease Registry, 2012; Longmire, 2015). Fortunately, TA-3 has ceased operations and there is no other active source of chromium-6 that could further contaminate the area (N3B Los Alamos, 2019).

With historical evidence that chromium migrates at speeds matching surface water and groundwater flows, chromium contamination is currently the laboratory’s highest priority in on-site clean-up (Longmire, 2015; S. Kovac, personal communication, 2020). A Chromium Plume Control Interim Measure (IM) is currently being enforced by the DOE. The IM is a series of actions fully implemented in 2019 that LANL must make in order to meet environmental protection goals until the DOE can implement a final remedy to the contamination (N3B Los Alamos, 2019). The primary goal of the IM is to control expansion and limit downgradient migration of the plume as the DOE investigates options for a final remedy (DOE Environmental Management Los Alamos Field Office, 2015).