Vadose Zone Transport of Tritium and Nitrate under Ponded Water Conditions

Journal Article · 27 July 2022 · Geosciences

DOI: https://doi.org/10.3390/geosciences12080294 · OSTI ID:1881806

Stauffer, Philip H.  ^[1]; Newman, Brent David  ^[1]; Birdsell, Kay Hanson  ^[1]; Gard, Marvin Ormond  ^[1]; Heikoop, Jeffrey Martin  ^[1]; Kluk, Emily Cecile ^[1]; Miller, Terry Ann  ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Vadose zone transport of tritium and nitrate can be important considerations at radioactive waste sites, landfills, or areas with industrial impacts. These contaminants are of particular concern because they typically have a relatively higher mobility in the subsurface compared to other compounds. Here, we describe a semiarid site with tritium and nitrate contamination involving a manmade ponded water source above a thick unsaturated zone at Los Alamos National Laboratory in New Mexico, USA. This study demonstrates the value of vadose zone flow and transport modeling for the development of field investigation plans (i.e., identifying optimal borehole locations and depths for contaminant characterization), and how a combination of modeling with isotope and geochemical measurements can provide insight into how tritium and nitrate transport in the vadose zone in semiarid environments. Modeling results suggest that at this location, tritium transport is well predicted by classical multiphase theory. Our work expands the demonstrated usefulness of a standard tritium conceptual model to sites with ponded surface conditions and agrees with previous results where a standard model was able to explain the evolution of a tritium plume at an arid waste disposal site. In addition, depth-based analyses of δ¹⁸O and δ²H of pore waters helped confirm the extent of pond infiltration into the vadose zone, and the δ¹⁵N of nitrate showed that the contaminant release history of the site was different than originally assumed.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Environmental Management (EM)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1881806
• Report Number(s): LA-UR-17-23079
• Journal Information: Geosciences, Journal Name: Geosciences Journal Issue: 8 Vol. 12; ISSN 2076-3263
• Publisher: MDPICopyright Statement
• Country of Publication: United States
• Language: English