More than 40 years after contaminated water was dumped into canyons around Los Alamos and nine years after they started studying the problem, the US Department of Energy now has a short-term strategy for dealing with a plume of toxic chromium that's been moving slowly off Los Alamos National Laboratory and toward San Ildefonso Pueblo and the regional aquifer. Not quite undertaking a total cleanup of the contamination, the feds rather intend to do enough to stop its migration. Generally, according to a plan released this week, they'll watch for its next move.

The chromium has been traced to the use of a chemical compound to prevent corrosion in cooling tower water in the lab's power plant from 1956 to 1972. That water, including an estimated 31,000 to 72,000 kilograms of hexavalent chromium, was discharged and has since seeped into the aquifer.

Monitoring wells there have recently detected chromium at levels that exceed the 50 parts per billion allowed by New Mexico's groundwater standard. Concentrations at the center of the plume have been found as high as 1,000 ppb.

Exposure to hexavalent chromium has been associated with an increased risk of cancer, according to the Agency for Toxic Substances and Disease Registry. The lab, of course, is situated mostly on mesas on the Pajarito Plateau above canyons that drain east to the Rio Grande. And the plume has already moved two miles down the canyons from where the cooling water was released.

A contaminant plume estimated to be one mile long, a half mile wide and 100 feet thick is thought to be within half a mile of the nearest drinking water well; it is now floating in the top 100 feet of the regional aquifer.

The latest groundwater tests suggest it is continuing to move, toward the Pueblo boundary and beneath neighboring cultural sites, and the Department of Energy's proposed plan is to stop that movement. Two groundwater extraction wells will annually remove 230 million gallons of water contaminated with hexavalent chromium, or chromium-6, then treat it with an ion-exchange system to become the less hazardous form, chromium-3, for the eight years of the project. Treated water may be injected back into the ground through six wells the DOE has proposed to drill, or poured over the ground surface. All work is intended to be timed appropriately to do as little as possible to disrupt Mexican spotted owls, which are known to nest in the area.

Beyond that, the DOE proposes ongoing monitoring and study of potential corrective actions to extend past this so-called interim measure.

Monitored natural attenuation—just watching the plume of contaminants to see if it dissipates into the environment and is naturally diluted to safer levels—is still a possibility for a final remedy selected by the DOE.

New Mexico Environment Department Secretary Ryan Flynn described this approach as among his least favorite options when he spoke at a November meeting on LANL's wide-ranging cleanup programs. The Environment Department approved the interim plan with some modifications in October, pointing to concerns that the level of chromium found at some wells is higher than expected, suggesting the "overall flux of [chromium] migrating offsite could be more extensive than previously thought." That the water samples taken at the boundary well show twice the groundwater standard level for chromium and the proximity to a groundwater well for Los Alamos County suggests "the possibility of the well becoming vulnerable to contamination."

"Here we are more than 40 years after the last chromium was dumped into Sandia Canyon, and we are now starting cleanup," Nuclear Watch New Mexico's Scott Kovac writes SFR in an email. "This shows the Lab's preferred cleanup method, 'natural attenuation,' is really not cleanup at all. It's time to start comprehensive cleanup across Los Alamos, instead of hoping for the contaminants to go away."

Addressing the chromium plume, which had not yet been identified when the current consent order governing the cleanup at the lab was finalized in 2005, has required a significant portion of the budget and work effort at the lab. The focus of the work to date has been on groundwater monitoring and characterizing the plume.

Danny Katzman, technical lead for the chromium project, says the plume presented an incredibly complex problem that took serious study to understand.

"It's taken nine years to mature our understanding to know what action needs to be taken," Katzman told SFR in November. The worst solution, he said, would be one that created another problem in the process, and their aim has been to avoid that.

The chromium project has contributed to delays and an estimated 150 deadline extensions, including, of course, the deadline for what was to be the last of the cleanup at LANL, which had been set for Dec. 6, 2015.