Chemical contamination more than four times the state limit was detected late last month at the edge of a plume in the aquifer roughly 1,000 feet below Los Alamos National Laboratory.
It is the closest high-level measurement of hexavalent chromium detected near the well used to pump drinking water to Los Alamos County, roughly a third of a mile away.
“Our drinking water supply is safe, and we are vigilantly working to keep it that way,” said Tim Glasco, utilities manager for Los Alamos County.
Hexavelent chromium, an industrial chemical tied to lung and other cancers, was found pooled below Sandia and Mortandad canyons in 2005, and environmental managers have since been working to define the full scope of the contamination. It spans at least a mile long and half-mile wide, and abuts San Ildefonso Pueblo.
The aquifer contamination was created by decades of dumping water used in cooling towers that was laced with chromium. Workers dumped the water into Sandia Canyon between the 1950s and 1970s. The water traveled several miles downstream to Mortandad Canyon, seeping into the ground to form the plume.
After contamination was detected at eight times the state standard in 2005, the lab paid the state Environment Department a $250,000 fine, in part for delaying its reporting of the contamination.
A 2016 cost estimate said cleaning up the hexavalent groundwater contamination could extend until 2048 and cost more than $180 million.
A new well, designated R-70, was drilled earlier this spring in the outer, eastern edge of the plume, an area that had not yet been sampled for the chemical. A May 27 sample, posted to the online data portal Intellus New Mexico, shows results of 238 micrograms per liter, or parts per billion. The New Mexico groundwater limit is 50 parts per billion.
That sample was taken from a deeper level of groundwater, while a more shallow sample showed just 13.6 micrograms per liter.
Glasco says his staff was notified of the high reading a couple weeks ago.
“Obviously we are not pleased with that,” he said. “But it is not altogether unexpected. … It was more of a confirmation.”
Glasco said there is no contamination higher than state standards in the well used to pump groundwater for the county or at two closer wells that were drilled to detect encroaching contamination. These wells are tested monthly.
“It is really more of a wait-and-see at this point,” he said.
While Glasco stressed the county’s drinking water is safe, he said a secondary well has been drilled a mile and a half away from the plume that could be used to provide drinking water to the county if the existing well must be shut down. The county also has considered treating the water, should high levels of chromium be detected, to bring it back below state standards, likely through a dilution process.
Dozens of wells dot the landscape surrounding the suspected perimeter of the plume, but there are still questions about its full extent and contamination levels. In 2017, a well that officials expected to be free of contamination — and intended to use to inject clean water into the plume — was found to have more than five times the state limit of hexavalent chromium.
As a result, the lab had to redraw the shape of the plume. On the new map, a light purple is shaded to show the plume’s location, but the eastern edge is dotted with question marks.
The R-70 well was drilled to better identify the true extent of the plume, at a cost of millions of dollars. The eastern edge previously had no monitoring wells.
Environmental managers hope to temporarily stall progress of the plume through a “pump and treat” method, where contaminated water is pumped out of the aquifer, treated and reinjected.
Doug Hintze, environmental manager for the Department of Energy’s Los Alamos field office, said at a meeting last month that efforts to treat the plume in the southern boundary shared with San Ildefonso found lower levels of contamination, closer to state standards.
Maddy Hayden, a spokesperson for the New Mexico Environment Department, which regulates the chromium plume, said the state “is evaluating the recent results to determine the next steps in addressing the contaminated groundwater and the extent of the plume near the Los Alamos County production well.”