title: Krypton-81 in groundwater of the Culebra Dolomite near the Waste Isolation Pilot Plant, New Mexico.
abstract: The Waste Isolation Pilot Plant (WIPP) in New Mexico is the first geologic repository for disposal of transuranic nuclear waste from defense-related programs of the US Department of Energy. It is constructed within halite beds of the Permian-age Salado Formation. The Culebra Dolomite, confined within Rustler Formation evaporites overlying the Salado Formation, is a potential pathway for radionuclide transport from the repository to the accessible environment in the human-disturbed repository scenario. Although extensive subsurface characterization and numerical flow modeling of groundwater has been done in the vicinity of the WIPP, few studies have used natural isotopic tracers to validate the flow models and to better understand solute transport at this site. The advent of Atom-Trap Trace Analysis (ATTA) has enabled routine measurement of cosmogenic (81)Kr (half-life 229,000 yr), a near-ideal tracer for long-term groundwater transport. We measured (81)Kr in saline groundwater sampled from two Culebra Dolomite monitoring wells near the WIPP site, and compared (81)Kr model ages with reverse particle-tracking results of well-calibrated flow models. The (81)Kr model ages are ~130,000 and ~330,000 yr for high-transmissivity and low-transmissivity portions of the formation, respectively. Compared with flow model results which indicate a relatively young mean hydraulic age (~32,000 yr), the (81)Kr model ages imply substantial physical attenuation of conservative solutes in the Culebra Dolomite and provide limits on the effective diffusivity of contaminants into the confining aquitards.
authors.affiliation: Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA. Electronic address: Sturchio@uic.edu.
authors.forename: Neil C
authors.initials: NC
authors.lastname: Sturchio
authors.affiliation: Repository Performance Department, Sandia National Laboratories, Carlsbad, NM 88220, USA.
authors.forename: Kristopher L
authors.initials: KL
authors.lastname: Kuhlman
authors.affiliation: Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA; Department of Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Reika
authors.initials: R
authors.lastname: Yokochi
authors.affiliation: Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Probst
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA; Department of Physics and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Zheng-Tian
authors.initials: ZT
authors.lastname: Lu
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Mueller
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA; Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Guo-Min
authors.initials: GM
authors.lastname: Yang
mesh_terms: D060587:Groundwater / Q000032:analysis*; D007726:Krypton / Q000032:analysis*; D007727:Krypton Radioisotopes / Q000032:analysis*; D008962:Models, Theoretical; D009516:New Mexico; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D007727:Krypton Radioisotopes; D014874:Water Pollutants, Chemical; D007726:Krypton
keywords: Flow model; Groundwater age; Krypton-81; Matrix diffusion; Transport