This heat map displaying data from 2017 to November of 2020 visualizes spots where sampling concentrations are below 50 ppb (blue), above 50 ppb (yellow), or above 100 ppb (red). It is clear that the shape of the plume has changed significantly within the past three years. It suggests that interim measure control efforts at the bottom of the plume are redirecting the contamination east, elongating the plume. While the objective of preventing the plume from crossing into Pueblo territory has so far been accomplished by the DOE, there is still concern that their current efforts are just delaying the inevitable and necessary full-scale remediation.

This is a map showing the boundaries of the plume outlined in pink, as estimated by the Department of Energy in 2019, as well as the locations of each sampling well in and around the chromium plume.

Chromium concentration levels have decreased from over 1200 ppb in 2008 to below 50 ppb since 2017. In 2017, the DoE began treating R-42 with sodium dithionite, aiding in decreasing the chromium concentration. This explains the sharp decline in 2017, but does not explain the drops in 2008 or 2014. Logically, treating a contaminated well upstream from more contaminated wells should theoretically lead to decreased concentration levels in those wells too, but this was not the case for R-28. Since its origin in 2005 this well has been steadily reading chromium levels around 400 ppb. Towards the end of 2017 these levels spiked sharply reaching as high as 1600 ppb. This could have been due to the sodium dithionite being injected in R-42 pushing the chromium downstream into R-28, but we are not certain. It was also around this time that LANL began a pilot-scale in situ treatment in which they poured molasses into this well. As depicted by the graph, the chromium levels immediately plummeted and fell below 50 ppb by mid 2018. The levels have remained below 50 ppb since with the exception of one reading near 1600 ppb in late 2019.

Chromium injection wells were installed along the edge of the plume with the Pueblo de San Ildefonso border in an effort to prevent contamination spread outside of technical area 5. These wells inject treated water that was extracted from the center of the contamination plume. As depicted by the graphs about, the injection wells have been effective in reduce chromium levels along the Pueblo border.

SIMR-2 is the lone monitoring well inside Pueblo territory along the border with technical area 5. So far the concentration levels in this well have remained below 50 parts per billion since its inception in mid 2015. This indicates that chromium contamination has not spread into the Pueblo lands.

CRPZ-2 is located in the center of the plume just upstream from well R-28. We marked this area for concern due to its close proximity to R-28, yet it never shared the same high readings. While the concentration levels are between 100 and 200 ppb and continuing with an upward trend, we are curious as to why this well is not seeing higher levels. Another thing to add about CRPZ-2 is that there were a lot more samples taken prior to 2018 before the concentration levels rose over 100 ppb.

Levels in chromium extraction wells 1 and 2 remain between 100 and 200 parts per billion. This indicates that the plume remains a threat in the area.

The levels in R-50 and R-61 remain just under 50 ppb. R-61 however, is increasing, and has jumped from 25 ppb to 40 ppb in the past two years. R-50 has dropped below 50 ppb in the past two years due to its location between chromium injection wells 4 and 5, which once again shows that the pump and treat method is working to keep the plume from entering the Pueblo. However, R-61 is the last well in-line with the Pueblo on the southwestern side of the plume, and based on the increase in the past two years, we are concerned that the plume is expanding in this direction.

In 2005, there were levels above 50 ppb, but they immediately decreased to 30 ppb in 2007. Suddenly, levels started to increase gradually, passing 50 ppb in late 2009, and reaching their peak in 2016 at 87 ppb. Levels have been decreasing for the past 4 years, which can probably be explained by the natural southeast groundwater flow that may be transporting chromium away from this well. Despite this trend, levels have remained above 50 ppb since 2009. The most recent sample was 61 ppb from August of 2020.

Regional well R-45 is south of CrEX-5 and R-70. Concentration levels have been gradually increasing since 2009 and are approaching 50 ppb. This graph includes two sets of data from R-45. The first set called Screen 1 is samples taken at depths between 880 and 890 feet below ground surface. The second set is called Screen 2 is samples taken at deeper depths between 975 and 995 feet below ground surface. As you can see, levels in both screens have been gradually increasing since 2009 when the first samples measured below 10 ppb. Levels in Screen 2, however, continue to increase and are nearing 50 ppb.