Title: Using groundwater noble gas measurements to confirm paleorecharge hypotheses at Pahute Mesa, Nevada National Security Site, Nevada, USA

Abstract

Pahute Mesa (Nevada, USA) was the site of 85 underground nuclear tests between 1965 and 1992 whose residual radio-chemical inventory poses a contaminant threat to local groundwater resources. To assess the fate and transport of these radionuclides in groundwater, several geochemical studies, including this one, have been conducted to understand long-term groundwater flow patterns at, and downgradient of, Pahute Mesa. Groundwater samples from the Pahute Mesa area at the Nevada National Security Site were analyzed for noble gases (³He/⁴He isotopic ratio and He, Ne, Kr, Ar and Xe concentrations) to infer groundwater recharge temperatures and provide additional evidence in support of groundwater flow patterns and the presence of late-pluvial Pleistocene groundwater. These data confirm recent findings (based on groundwater geochemistry and isotope compositions) that most recharge in the area occurred under temperature conditions much cooler than are found today, except near major drainages where ephemeral run of continues to recharge shallow groundwater. These noble gas data indicate that noble gas recharge temperatures and terrigenic He components have been reset where groundwater has flowed upward over barriers formed by caldera margins, or near the regional discharge area (Oasis Valley) where shallow groundwater has interacted with shallow soil gas. This evidence frommore » groundwater noble gas measurements, in combination with other isotopic and geochemical studies, supports the current understanding of the unusual hydrogeology and recharge history of Pahute Mesa.« less

Authors:

Visser, Ate  ^[1];

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Kwicklis, Edward ^[2]; Farnham, Irene ^[3]; Tompson, Andrew F. B. ^[1]; Hershey, Ronald L. ^[4]

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+ Show Author Affiliations

1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. Navarro-Intera, LLC (N-I), Las Vegas, NV (United States)
4. Desert Research Inst. (DRI), Reno, NV (United States)

Publication Date:

Thu Jan 06 00:00:00 EST 2022

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1860877

Report Number(s):

LLNL-JRNL-815880
Journal ID: ISSN 1431-2174; 1023824

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Hydrogeology Journal

Additional Journal Information:

Journal Volume: 30; Journal Issue: 1; Journal ID: ISSN 1431-2174

Publisher:

Springer

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; geochemistry; groundwater isotopes; noble gases; nuclear test site; USA