The US Department of Energy has released data from sampling the agency did at the Riverton Uranium Mill Tailings Radiation Control Act Site in August. The area, which is on the Wind River Indian Reservation, was contaminated with uranium and vanadium in the late 1950s and early 1960s, when a uranium mill processed ore there. In the ‘90s the DOE recommended waiting for natural dissolution to clean the site, and levels of contamination seemed to be diminishing predictably until a big flood in 2010. At that point, levels rose dramatically, and this new series of tests should help DOE to figure out why.
DOE’s Bill Dam is the site manager. Dam says there’s latent contamination in both the surface soil and shallow groundwater that washed out during the event.
“We know that the river flooded over the banks. That 2010 flood was 4 feet above flood stage. And so we know that there was flooding south of Rendezvous Road but also the flood caused a rise in groundwater, so it is a combination of both processes,” says Dam.
The DOE was able to sample 103 sites out of the planned 130 or so. The average uranium contamination level was about six times the benchmark limit, though some samples were closer to 50 times the limit.
But Dam says the shallow contamination does not affect drinking water, which comes from deeper aquifers.
“This contamination does not leak down into the deeper system. Just want to make sure that you know the contamination in the very shallow soil and groundwater is not impacting people’s drinking water,” says Dam.
The released numbers do not include analysis of the data. The report explaining what the numbers actually mean should be out this summer.