Locations of wells within the Chromium Plume Project. A Los Alamos County drinking water well, PM-3, can be seen in the top right corner of the map. Well R-70 is a third of a mile from PM-3 and R-45 is half a mile from PM-3. Map Courtesy EM-LA

Although there has not yet been public discussion by Los Alamos County Council of what’s going on with the Los Alamos National Laboratory’s Hexavalent Chromium Plume Project, the Los Alamos County Board of Public Utilities (BPU) and Utilities Manager Philo Shelton have been digging into the issue.

Shelton reported to the BPU last month on the Department of Energy Environmental Management Los Alamos (EM-LA) hybrid quarterly public forum, March 1, which featured the chromium plume as the main topic. He noted that there had been a lively online exchange between EM-LA and New Mexico Environment Department (NMED) staff.

Shelton reminded BPU members of a presentation the board heard from NMED staff in January 2022 where professional differences between the state and DOE about the behavior of the plume were aired. The key difference of opinion involves the reinjection of the treated groundwater into the ground and whether or not that could be pushing the plume further down towards the aquifer as NMED believes could be happening, or whether that water is actually creating a hydraulic barrier that is containing the plume.

“Because of the differences of opinion, I directed my staff last year not to operate the County’s well near the plume and I think it’s important for the community to know that we’re adjusting our operations and not delivering water from that location until we can really understand the nature and extent of what’s going on there,” Shelton said.

Om March 1, Tom McCrory, a senior geologist with EM-LA, gave a lengthy presentation for BPU members. He noted that EM-LA has close to 30 wells in the chromium project area compared to four in 2004, before the plume was discovered.

“The plume is almost 7,000 feet long from west to east. It’s almost 3,000 feet from north to south. The only blessing here is the regional aquifer here is 3,000-5,000 feet thick and most of the extent of this plume is actually confined to the upper 50-100 feet of the regional aquifer. It’s almost like a skinny pancake at the very top of the regional aquifer with the rest of the regional aquifer having only background concentrations,” he said.

McCrory described the five injection wells at what was believed to be the leading edge of the plume.

“You take the water out, you and you take send it to a central treatment facility, put it through an ion exchange resin which strips out the chromium and then you take the effluent from that treatment system which is drinking water quality and you put it back into injection wells into the regional aquifer,” he said. “You do this for two reasons – one is to attempt to get hydraulic control here. The other one is the State Engineer limits how much we can take out of the aquifer each year without returning it and even without this system we’re typically at 95-98 percent of the maximum so we’re right at the edge anyway.”

Well R-70 was installed in 2019 and EM-LA thought it would give them the eastern boundary of the plume.  There are a number of monitoring wells that have an upper screen and a lower screen, including R-70. When samples were taking from the lower screen at R-70, scientists were surprised that the lower screen contained much greater concentrations of hexavalent chromium.

“So, clearly as it migrates it gets a little deeper. This one is about 100-110 feet deep. It’s not going down very fast but it is starting to go down. We’re going to be doing more work to better define just how far has that gotten,”McCrory said.

He noted that the plume has been pulled back quite a ways from the Pueblo de San Ildefonso by a hydraulic barrier created by the injection of treated water from three wells over a period of several years.

McCrory listed three scenarios for EM-LA to operate in the future. The first is to continue to operate the way they have been operating. The second is to continue to use the pump, treat and inject system but at a reduced rate of about half of what EM-LA has been doing. The third option is land application. Once the chromium has been removed from the water, instead of injecting it into the aquifer, EM-LA would spray it onto the surface.

“Regulations for land application are extensive.  When you have all those restrictions you can only run the system at about 10 percent of what we’re doing right now and that’s a problem because that’s not enough the control the plume migration,” McCrory told BPU. “The fourth scenario is just turn the whole thing off.”

Asked how EM-LA evaluates how well the ion system is working. McCrory said water underground does the same thing it does above ground. It goes from high to low.

Asked if all the chromium that soaked into the ground has gotten to the regional aquifer already or is some of it still in transit down the 1,000 foot decline it has to go to get there, McCrory said, “Honestly, we don’t know yet. What we do is we make the most conservative assumption and that is to say, no, it’s not all gotten there yet”.

As for how long it would take the chromium to get down 1,000 feet, McCrory said the problem is it’s pretty easy to do once it’s in the groundwater.

“It moves along with the groundwater and we get a pretty good estimate of how long that is. This 1,000 foot interval has three very distinct kinds of lithologies each of which has their own dispersion coefficients, their own preferential pathways which are complicated. We can’t be sure. One way we’ll get some certainty is when we turn on a permanent system, which we hope to do as soon as possible and we start extracting chromium, we see chromium concentrations going down reasonably quickly, it gives us to believe – well it’s okay. It’s not being replenished. If we see the concentration staying the same or going down very gradually, it suggests that there’s still some replenishment going on,” McCrory said.

McCrory said the bottom line up front, is if EM-LA has to turn off the Interim Measure and leave it off the contamination is going to resume spreading.

“That’s probably not a surprise but it’s not good news,” he said.

McCrory said It looks like with the possible exception of the eastern end around R-70, given enough time EM-LA will be able to capture and remove – to get at some point to where there’s no chromium at more than 50 ppb in the groundwater anyplace, which is the ultimate goal.

During a question and answer period with BPU members, McCrory noted that the chromium level in Well R-61 has risen to 45 parts per billion.

“There is a hypothesis about why this is happening and that it’s actually a good thing that it’s happening.  We want to be pushing the plume back laterally towards the centroid so we can pick it up. What happens when you have a plume that’s this big, a matrix that’s this complicated, you almost never get 100 percent success off the bat. We’ve been getting 80 percent. That’s a good start, especially for an Interim Measure system that is a predecessor to the full operation. Now that we know this is happening at the eastern end with R-45 and R-70, as we put in the permanent system, we’ll make sure we have extraction screens deep enough to capture that as it goes through,” he said.

Asked if EM-LA has you ever considered injecting at a depth much deeper than the monitoring wells, McCrory said EM-LA  hadn’t looked at that historically because they wanted to create a hydraulic barrier that would stop the plume, which he said at the time was understood to be relatively thin – 50-70 feet.

“In fact over most of the plume length, that is about how thick it is. As we get out to the eastern end it gets deeper but that was only discovered after the IM system was installed and operating. As we go to the permanent remedy I will look at both extraction and injection at deeper levels,” he said.

McCrory said there is a belief that groundwater containing more than 50 ppb is actually moving across the Pueblo de San Ildefonso Pueblo boundary right now and that there is talk that it is the operation of the ion system that is causing that.

“It kind of puzzles me because we have five monitoring points on Lab property just a few hundred feet north of the Lab boundary. With the exception of R-61, all of them now are on background.  R-61 is up around 45-46 ppb. But the thing is Crex 2 is an extraction well. Extraction wells by their nature pump water out of the ground and water is drawn in from the surrounding area to the extraction well so if in fact Crex 2 is having an effect on R-61, it’s going to be pulling water to the north, which of course is away from the boundary,” McCrory said. “I’m particularly concerned that if we’re not allowed to start up Crex 2 again, it lets whatever is going on down there resume its natural flow which is something I don’t think we want to do. We hear those claims in meetings with people. It’s very distressing to us.”

He said to his knowledge there isn’t data to support that and that the well on the Pueblo de San Ildefonso has always been at background.

“We don’t see any evidence that anything  that exceeds safe drinking water level is moving across, but because it has been brought up to us, I thought we should mention it in case people here had heard it,” he said.

McCrory said moving on and taking all of this information and putting it together, EM-LA uses modeling simulations to look at changes in concentrations for the four different scenarios.

“The full operation scenario which started in the southern part in spring of 2018 and the eastern part in fall of 2019 and ran that way until fall of 2022; the reduced operations, which we’re currently under per the direction of NMED which is around half that rate and two extraction and two injection wells; the land application, which we are not doing, and which would cut us back to about at very best 10 percent of the rate at which we can extract now, which wouldn’t frankly do a whole lot of good; and then no operations at all, which  would be just turn it off, which is what the Groundwater Quality Bureau is saying we’re going to proceed to do on April 1, unless you persuade us otherwise in the meantime. And then the full operation is when all five extraction and injection wells are running,” he explained.

McCrory said given the changes in the R-45 Screen 2, there’s a possibility that EM-LA might want to leave the injection wells nearest to it off just to see what transpires, but that it had not been decided if that would be a reasonable experiment to do.

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