BY MAIRE O’NEILL
N3B, the legacy waste cleanup contractor for Los Alamos National Laboratory’s Middle DP Road Site has added a link for update to the cleanup effort to its website at https://n3b-la.com/middle-dp-road, N3B’s Acting Environmental Remediation Manager Troy Thomson told Los Alamos County Councilors during their May 18 work session
Thomson discussed the investigations being conducted on two land parcels, A-16A and the adjacent A-8A on DP Road that are south and east of the Bethel development where previous investigation work has been done. The two parcels are owned by Los Alamos County and they were formerly owned by the Department of Energy prior to being transferred to the County for residential use. Thomson said the purpose of the Middle DP Road project is to determine the extent of any contamination and remove the previously discovered contamination that was identified in previous excavations. Also, he said if any new contamination is identified, the best path forward for its removal will be determined.
The work plan for the site which is called a Solid Waste Management Unit, was approved by New Mexico Environment Department.
“The approach we’re taking is to excavate down to native tuff at approximately 125 locations based off the 35-foot triangular grid pattern. Really we’re looking for contaminated debris or waste disposal areas that could be present in the areas,” Thomson said.
He noted that some geophysical surveys have been conducted in the area and that some of the potholes picked up some anomalies and based off the resulting reports, N3B wants to do some additional investigation.
“We’re also going to excavate previously identified debris locations and in those areas we’re going to define the extent of the debris and the contamination and then go about a removal and cleanup of those items. We will also conduct sampling to define nature and extent of potential contamination around those areas and ultimately evaluate the risk to human health and ecological receptors,” Thomson said.
While the work is being performed, N3B will also conduct air monitoring, storm water run-off control, typical site inspections and confirmatory samples as well as some waste disposition and ultimately some reporting and stakeholder interaction. Parcel A-8A hes mostly been completed and N3B is not concentrating a little more on A-16A, Thomson said.
“We have completed 50 locations and 2 anomalies on A-8A and 21 locations on A-16A, so 73 of the roughly 125 locations have been investigated to date. If we do find contaminated debris at any of these locations, we will work with DOE to determine the steps required for remediation at those locations,” he said. “Consistent with the current planned land use, the Middle DP Road site will be cleaned up to meet residential and construction work use scenarios.”
The field work, which began in April, has been going pretty well so far, Thomson told Councilors.
“We do expect some of the cleanup at the known contamination areas will take a little longer than the potholing we’ve done now but we’re expecting field work to be complete in the fall of 2021,” he said.
He noted that some of the businesses along DP Road have recently been briefed and that N3B does not expect any road closures, delays or detours during the project.
“We will continue to brief as requested or if something changes and we need to provide additional updates. If we are going to have some impact on the road, we would use limited duration of spotters or flaggers to make sure we’ve got safe vehicle entry and exit from the site onto Middle DP Road. We’ll continue to coordinate with Los Alamos County and the housing developers to minimize any additional impacts to access along DP Road,” Thomson said.
He noted that to date, the excavations have gone well but N3B expects at times the potential for contaminated debris in some of the potholes.
“That’s going to help us find nature and extent because we do know in the areas specifically around the lift station and along the original trench on the A-16A parcel that we do have some known contamination that we’re going to have to go remove and cleanup. Identifying something will not be unexpected to us and we do have plans in place to be able containerize that, handle it and ultimately do the cleanup associated with the Middle DP Road Site,” Thomson said.
In response to questions from Council, Thomson explained that geophysics anomalies will pick up something in the subsurface that is not quite as expected. He said an abandoned utility line was found that was also not in Department of Public Utilities maps. The lone was checked for contamination, he said.
“As most of you may be aware, there was a trailer court that was located in the A8-B parcel for many years in the 50s and 60s and some of that infrastructure is more likely what we’re finding. I know we found some yellow-wrapped pipe as well which is typical of gas lines for an area. It’s something that the geophysics detected that wasn’t quite consistent with the surroundings and could indicate some disturbed area and we wanted a little more looking in those areas to make sure that we’ve done our due diligence as we’re checking out the sites,” Thomson said.
He explained that geophysics companies use electromagnetic instruments and walkovers with ground-penetrating radars and can tell where the ground has been disturbed or is undisturbed.
“Our geophysics company put together a report outlining the anomalies and has identified where we would like to do some additional investigation,” Thomson said.
He also explained that the potholes are excavated with heavy equipment and go down until they reach native tuff.
“Depths towards the southern boundary are 1-2 feet. As you approach the canyon rim, there’s not as much surface cover with the soil in those areas. Some we’ve had at 11 feet. I expect from the previous trench that was dug through A-16A there were depths of 10-15 feet and I would expect we would encounter that as well as we continue to pothole,” he said.
Per the Preliminary Site Plan approved by NMED, Thomson said N3B is looking for debris, typically Laboratory debris, but that any debris found is surveyed whether it’s a brick from a construction activity or discoloration and other issues in the soil.
“If we identify areas of concern, we are doing additional radiological screenings on the soils in other areas at that time. We will be segregating some of the debris for waste disposition analysis as we go along but we will also be collecting waste samples and doing confirmatory sampling as we complete the cleanup. We will be doing additional boreholes around the areas that we have excavated making sure that we have identified full nature and extent prior to completion of this work.” Thomson said.