Joel Hebdon
N3B Deputy Manager
Environmental Remediation
By KIRSTEN LASKEY
Los Alamos Daily Post
kirsten@ladailypost.com
The Environmental Management – Los Alamos Field Office (EM-LA) and its contractor, N3B are grappling with how to solve a 22-year-old mystery.
The hexavalent chromium plume was first detected in 2004, N3B Deputy Manager for Environmental Remediation Joel Hebdon told the Board of Public Utilities (BPU) during a May 20 meeting at the Municipal Building. The plume, which is in the regional groundwater aquifer 1,000 feet beneath Mortandad and Sandia Canyon at Los Alamos National Laboratory (LANL), was determined to be above the New Mexico groundwater standard of 50 micrograms per liter, Hebdon said.
While he emphasized that the chromium does not pose an immediate threat to public or private drinking water wells, how to stop the plume’s migration and fully treat the water is still being investigated.
As an interim measure, Hebdon said a pump and treat system is being utilized. He explained that water is pumped out of the aquifer and into an ion exchange column to be treated and then into a second column to be treated again. Once the water is cleaned, it is pumped through an injection well back into the aquifer. Hebdon said the system operates at 240 gallons per minute and that 120 million gallons are treated annually.
However not all the water is caught, he said, adding that a series of studies are being conducted to consider how best to configure these wells to stop the entire migration of this plume. A study plan is being developed right now “to spell out the necessary remaining investigations not just into the geo-hydrology and the behavior of the plume but also how to best optimize this system, capture as much chromium as possible, remove it from the aquifer and move that clean water back into the aquifer.”
It was pointed out during the BPU meeting that the amount of chromium removed has been very small – 860 pounds has been removed compared to the estimates of a couple hundred thousand pounds that exist in the groundwater.
“We don’t know exactly how much is in the aquifer,” Hebdon said. “I got an estimate, but I don’t want to share it because I don’t know how close it is.”
He added that he thinks there is somewhere around 160,000 pounds that were released into an unlined ditch that then traveled into the soil and then into the aquifer, but it isn’t known how much of that is in the aquifer. The hope, Hebdon said, is to know more through the studies.
This mystery originated from 1956-1972 when hexavalent chromium was believed to be used as a corrosion inhibitor at a LANL power plant at the head of Sandia Canyon. Its toxicity was not understood at the time.
The pump and treat system has gone through several starts and stops since 2018, Hebdon said. New Mexico Environment Department (NMED) requested the system shut down in 2020 due to COVID. It resumed in 2021, but Hebdon said NMED requested a partial shutdown of several of the injection and extraction wells in 2022. In 2023, there was a total shutdown and a limited restart in 2024. Then there was another total shutdown in 2025.
The Los Alamos Daily Post reached out to EM-LA for the reasons behind the frequent shutdowns. EM-LA officials responded that in 2022, NMED based its direction to shut down the system on a data point from one of the monitoring wells that showed the chromium concentration was increasing. NMED also alleged that the nearby injection wells may have forced the contamination deeper into the regional aquifer in the Eastern area. NMED then recommended resuming operations in 2024 before ordering them to cease in 2025. According to a letter EM-LA received from the state in 2025, the order was due to “recent analytical results showing the sole source regional aquifer beneath the Pueblo de San Ildefonso exhibits hexavalent chromium concentrations exceeding the regulatory standards …” Since March, EM-LA has been disputing the shutdown order and working on a resolution.
Looking at charts for contamination at several wells, Hebdon said the spikes and decreases in chromium are parallel to when NMED requests that the pump and treat system shut down or restart.
In showing a chart for Well R-50, which is at the property line between LANL and Pueblo de San Ildefonso, Hebdon said, “There is a trend up until the start of the IM (interim measure), then there is a little bit of a lag and then we get a quick drop of concentration of chromium … all the way down until we are asked to shut down, it bumps up again, a little bit of a lag, it bumps up again, until we restart and then concentrations of chromium again decreases until we are asked to shut down and then they bump up again …”
Then again, showing a chart for another well, at the same location, just 100 feet deeper than Well R-50, Hebdon said the chromium contamination level is close to the level that makes it impossible for the laboratory to discern that it is even there. It is close to zero.
It was asked if these charts were consistent with EM-LA’s modeling and how do the ground flow models compare to the data.
“We have been constrained – just like the state has asked us to shut down several times, they have also limited our ability to punch deep holes,” Hebdon said. “There’s some reasons for that. There’s concern that contamination might be entrenched deeper into the aquifer. We hope that very soon we will be able to get some deeper wells … where we will be able to see deeper into the wells …”
It was also asked how predictive the models are and how well they work.
The models work very well but there isn’t a lot of data, Hebdon said. He added there is a limited number of wells and there are constraints on where they are placed.
“All we can do is what we can do with the data we got,” he said, although data points are being added all the time.
Hebdon further noted that looking at a predictive model starting in 2016 through last year of the concentration of chromium, based on the state’s concentration limit of 50 micrograms per liter, this model shows that the plume is shrinking.
The interim measure is effective, he said.
“It shows that the plume is shrinking even when we have these disruptions. In other words, the pump and treat system is so effective that we can survive those periods where we are not actively extracting and injecting water – the capture is still relatively effective. Obviously, it could be much more effective if we were turned on all the time but even when we are not on all the time the pump and treat system seems to be very effective.”
When asked what the goal is; is it to get the chromium below the NMED groundwater standard of 50 micrograms per liter, Hebdon said that is the goal for the interim measure. The final goal is yet to be determined.
Hebdon’s presentation focused solely on the aquifer. When asked about the course of action for treating any contaminated soils, he said, “We’re looking into it. It’s extremely difficult to go after chromium in a 1,000-foot soil column.”
There are any number of ways to remediate it, Hebdon said. It could be capped in the places where the contamination enters the ground, liquids could be injected that would react to the chromium and lock it into place.
At this point, it appears to be just another mystery.