Soil radionuclide concentrations and preliminary stormwater model assessment at Material Disposal Area G, Los Alamos National Laboratory

A professional paper submitted in partial fulfillment of the requirements for the degree of Master of Water Resources Administration, Water Resources Program, University of New Mexico. April, 1999Material Disposal Area G (MDA-G) is at Technical Area (TA) 54 at Los Alamos National Laboratory (LANL). MDA-G has been the principal facility for the disposal of low-level, solid mixed, and transuranic (TRU) waste since 1957, it is currently LANL's primary facility for radioactive solid waste burial and storage. As part of the annual environmental surveillance effort at MDA-G, surface soil samples are collected around the facility's perimeter to characterize possible radionuclide movement off the site through surface water runoff. During 1998, 39 soil samples were collected and analyzed for percent moisture, tritium, plutonium-238 & 239 and americium-241. The results from these samples are compared with baseline or background soil samples collected in an undisturbed area west of the active portion MDA-G to assess radionuclide levels. The 1998 results are also compared to the results from analogous samples collected during 1996 and 97, to assess changes over time in radionuclide activity concentrations in surface soils around the perimeter of MDA-G. The results indicate elevated levels of all the radionuclides assessed in MDA-G surface soils vs the baseline soils. The comparison of 1998 soil data to previous years indicates no significant increase or decrease in radionuclide concentrations; an upward or downward trend in concentrations is not detectable at this time. Continued annual soil sampling will be necessary to realize a trend if one exists. The radionuclide levels found in the perimeter surface soils are significantly above background but still considered relatively low (particularly considering the amount of low-level radioactive waste that has been disposed of at MDA-G over the past 40+ years). The data do indicate that some radioactive material is moving off the site via the surface water runoff/sediment pathway, but in low quantities, which would not be considered a significant risk to human health or the environment. This perimeter surface soil data will be used for planning purposes at MDA-G. Techniques to prevent sediment transport off-site will be implemented in the areas where the highest radionuclide concentrations are indicated