BY MAIRE O’NEILL
It seems the virtual Northern New Mexico Citizens Advisory Board meetings have been the best place in recent months to hear what’s going on with legacy waste cleanup at Los Alamos National Laboratory and the Jan. 13 meeting was no exception. Under an agenda item that just read “Update from EM-LA – Kirk Lachman”, there was major news on both the Chromium Project and the RDX project. Lachman is the Department of Energy Environmental Management Los Alamos Field Office Manager and he announced that Danny Katzman, Technical Manager for N3B, and the Chromium Project lead since 2006, would be bringing the CAB up-to-date on both the RDX and Chromium groundwater programs.
Katzman discussed the Interim Measure that DOE has been implementing on the Chromium Project which he said has always been one of the highest priority projects because of the close proximity of the plume to the Los Alamos County water supply wells and proximity to the San Ildefonso Pueblo boundary. He said the fundamental design of the Interim Measure is to address migration of the plume while the long-term remedial alternatives are being evaluated. The process that’s in use is called “pump and treat”, which involves extraction of contaminated groundwater from the regional aquifer more than 1,000 feet below ground to the surface. The water is piped to a central treatment facility where it is treated by ionic exchange to remove the chromium.
Studies for other remedial alternatives are also being conducted, Katzman said including an in situ or in place remediation where the goal is to actually try to chemically change the chromium in the groundwater right in the aquifer.
“It wouldn’t even involve pumping groundwater to the surface for treatment. The treatment would occur by altering the material chemical conditions in the aquifer itself,” he said.
Katzman explained that the plume is composed of hexavalent chromium which is the form of chromium that one would expect to be relatively mobile.
“It’s soluble in water and generally moves as groundwater moves, but it’s very easy to manipulate hexavalent chromium and convert it into trivalent chromium by changing the oxidizing conditions in the aquifer to reduce the conditions.The way we’ve been exploring that is through a very small scale pilot study using two of the wells in this plume with two forms of amendments that we’ve injected into the aquifer for this purpose – sodium dithyanide and molasses,” Katzman said. “The idea was that we would seek to create reducing conditions using those amendments and then the condition in the aquifer would actually set up so that groundwater with hexavalent chromium in it flows through that reactive zone and converts to trivalent chromium, which becomes immobile and essentially inert in the environment, which is known to be a one-way geochemical reaction so that it doesn’t convert readily back to the hexavalent chromium.”
He said that study has been underway now for about three years.
“We’ve seen a couple of interesting things. We’ve seen the strong reducing conditions set up in the aquifer continue to treat the chromium in that area. Well R42 at one point had reports of 800 parts per billion (ppb) and we’re seeing concentrations there that are very low – generally in the non-detection range – around 5 ppb. Similarly in Well R-28 where they were 400 ppb before the test and continue to be very low – less than 10 ppb,” Katzman said. “That’s the upside of it.”
He noted that some potentially adverse conditions have also occurred from the tests and there have been some other challenges including the ability to understand the radius of effect around the injection points.
“It’s very difficult to know how big an area we’re treating. When you use in-place or in situ strategies like this, it’s very important that you know that you’re actually getting effective coverage in the area that you’re intending to treat and we’re starting to come to the understanding that that’s going to be very, very difficult to do here,” Katzman said.
The bottom in the Chromium Project discussion appeared to be that based on the success of the Interim Measure to date DOE is proposing to conduct an accelerated additional “pump and treat” process because the other two amendments did not see to work. Monitoring and characterization of the chromium plume itself based on the results of the first Interim Measure would continue.
“Following the Corrective Measures Evaluation (CME) process and all that it holds, it would be four or five years before we would be formally into remediation versus this accelerated approach which I think would get us there much quicker,” Katzman said.
Asked if the accelerated action would supersede the CME, Katzman said it would.
“The Consent Order allows the accelerated corrective action process when a remedy is presumptive so what it would do is allow us to move into that approach, understanding of course that it’s not just that you put something out there that says that you’re going to do pump and treat and get back to you when we’re done,” he said. “There’s still a strategy within the pump and treat aspect of it that would be a phased approach, that various phases would be informed by previous phases and it would be optimized along the way.”
He said the distinction between that and the CME is that in the CME, multiple technically viable remedial alternatives are brought to the table and ranked based on a number of criteria.
“We really don’t have multiple alternatives that we think we can bring to this, so because the Consent Order allows the presumptive approach to be applied in accelerated corrective actions, we think it offers all of us a really great opportunity to just get busy in just taking care of this thing and start really honing in on attacking the plume versus conducting what effectively is a pretty long process to evaluate alternatives that really don’t exist for us here,” Katzman said.
He said he doesn’t think it would behoove DOE to make any assumptions that NMED is ready to accept the proposal and that initially it would involve working with NMED staff to see if they’re seeing things the same way.
“The Consent Order requires once we’re at that point for us to issue an accelerated corrective action plan. The plan itself is still subject to NMED review and approval so it shouldn’t be viewed as an at risk type of thing where we would just go off and do the work and hope for the best. It still requires very active involvement and ultimately approval by NMED of an accelerated corrective plan. Assuming that we can get aligned on this, the next step would be to generate that accelerated corrective plan, get it in for review and approval, and then go from there,” Katzman said.
He explained that monitoring of the pilot scale amendments testing would also continue and that accelerated completion of the test is also being considered.
“We’ve kind of been stuck in a situation where we’ve only been able to conduct the pilot test in a passive mode and so how to complete that test is one of the things that we’re still looking at. I think the drive to complete the test and develop the sound technical case for how the study went feels less important now because again, we’re already seeing some things that we think don’t really bear on being the basis for continuing to invest money in a study that doesn’t feel like it’s going to lead us to a place,” Katzman said. “We are reserving the possibility that in the future if there’s some other really difficult part of the plume to tackle, it could still be a possible additional remedy approach to apply but I think that would be so many years down the road that I don’t see it as part of our primary or first order remediation strategy.”
On the second groundwater plume, the RDX plume, Katzman said DOE has submitted a deep groundwater investigation report in August 2019 and in May 2020 submitted a companion risk assessment that “concluded that there’s no imminent risk tied to the RDX contamination”.
“We also evaluated future potential risk because of course these groundwater settings are dynamic and this isn’t like a soil site where their condition is static because of groundwater flow and movement of contamination. We evaluated long-term risk as well and looked into the future using numerical models,” he said. “The imminent risk we think is addressed fundamentally through institutional control. The risk assessment for something like that for the RDX tap water screening level requires a complete pathway to a hypothetical receptor and this site is not only on DOE property, but within a high security area within DOE property so it’s very straightforward to invoke institutional control as the way to isolate the contamination from any potential exposure.”
Katzman said scenario evaluated the possibility of a rogue well being drilled somewhere in the area.
“That’s not possible here. The imminent risk is considered non-existent because of the institutional control, and then modeling was done to evaluate long-term risk and that basically evaluates whether or not the footprint of the plume could expand substantially over time. The three water supply wells would potentially be the first way for a pathway to a receptor become complete. The plume would have to migrate into a water supply well and ultimately work its way to receptors,” he said.
He said the long-term migration of the plume was evaluated and the report presents that “the plume is expected to have very, very limited migration for the foreseeable future and really has zero probability of arriving at the water supply well”.
“Our recommendation in those reports was that this project is well-suited to move into a long-term monitoring mode which would utilize not only existing wells but would also involve an evaluation of the need for potential additional wells to fill out the long-term monitoring network,” Katzman said. “A really important point I want to make about that is that the long-term monitoring concept would be such that it would use a multi-tiered approach where we would ensure that we had clear metrics for identifying evidence of plume migration either consistent with or different from that predicted by the models to give ample opportunity to apply any kind of response action that might be necessary if there was something about our numbers that weren’t holding true.”
In terms of long-term monitoring, Katzman said it’s important to note that existing wells would certainly be used but DOE would also be proposing to do an evaluation that would identify data gaps in the long-term monitoring and fill those as part of that overall strategy. He said it’s also important to note that the risk assessments hinge on DOE’s interpretation of the applicability of the tap water screening level.
“That’s a really important aspect of all this. The screening level for RDX is 9.66 ppb. In the regional aquifer are two known locations that exceed that value. In both of those locations the concentrations of RDX are 20 ppb or less, so roughly at the maximum two times the tap water screening level in a fairly limited footprint. We do anticipate that there is a possibility that additional wells would be necessary to fill out that long-term monitoring network,” he said. “I think it’s important to point out though that because this plume we believe is probably set in this location, without significant expansion for possibly even decades, we don’t see that the need for those additional wells for the long-term monitoring network are a particularly high priority at lease when compared to the chromium project wells where the importance of the proximity of the San Ildefonso boundary and the Los Alamos County water supply wells but that they certainly are more of a priority than that.”
Following Katzman’s presentations, Neelam Dhawan, NMED’s Permit Manager for LANL stressed that no agreements have been reached with DOE on how to proceed with either plume.
“Characterization is not complete at both these plumes, so we will engage with DOE in these discussions and see where it goes,” she said.
Dhawan said NMED does not have agreement with DOE on how to proceed with RDX.
“We don’t believe at this point that the correct action at this point would be to simply leave it in place and monitor it. We have had some discussions with DOE and we anticipate more coming along here,” she said.
On the chromium plume, Dhawan noted that the presumptive remedy proposal had been brought to NMED and that NMED hasn’t really had a chance to react to it.
“We’re always looking to move remedies forward faster if that’s advisable. We have some work on that to figure out what exactly the proposal is and how to go about that. You’ll be hearing more about that in the future. I just wanted to make sure you understood what our position was now on RDX and alert you that we really haven’t had conversations with DOE on the presumptive remedy.”