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Evaporation effects on oxygen and hydrogen isotopes in deep vadose zone pore fluids at Hanford, Washington

Donald J. DePaolo, Mark E. Conrad, Katharine Maher and Glendon W. Gee
Evaporation effects on oxygen and hydrogen isotopes in deep vadose zone pore fluids at Hanford, Washington
Vadose Zone Journal (February 2004) 3 (1): 220-232

Abstract

Stable isotopes of O and H were measured in pore fluid extracted from a sediment core located in a relatively undisturbed area in the Hanford site near the S-SX Tank Farms. Pore fluids from most of the 70-m-thick vadose zone section have delta (super 18) O values that are shifted to higher values than those for winter precipitation (and Columbia River water) by 3 to 4 per mil. The shift of delta (super 18) O and the delta (super 18) O-delta D slope of about 4 in the deep vadose zone pore fluids is attributed to partial evaporation during residence in the upper meter of the soil section. A model relating the isotopic shift to recharge and soil properties suggests that the shift should be inversely proportional to recharge, and larger for coarser soils with lower water retention. When applied to Hanford soils and precipitation patterns, the model predicts that vadose zone pore fluids at Hanford should typically be shifted by +2 to +6 per mil in delta (super 18) O relative to the values in wet season precipitation, even for relatively high values of annual net infiltration (up to 100 mm yr-1 or 60% of annual precipitation). The model has implications for groundwater as well as vadose zone delta (super 18) O. The effects of vegetation are not included, so only upper limit values for the net infiltration flux can be inferred from vadose zone delta (super 18) O. The shifted delta (super 18) O of natural pore fluids allows identification of the presence of subsurface water that comes from industrial discharges at the Hanford site. An example is provided by a low delta (super 18) O, high water content horizon at a depth of 44 m in the core, which is interpreted as industrial water that was transported laterally above a capillary barrier as a result of a nearby, near-surface point discharge that happened within the past 50 yr.


ISSN: 1539-1663
Serial Title: Vadose Zone Journal
Serial Volume: 3
Serial Issue: 1
Title: Evaporation effects on oxygen and hydrogen isotopes in deep vadose zone pore fluids at Hanford, Washington
Affiliation: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA, United States
Pages: 220-232
Published: 200402
Text Language: English
Publisher: Soil Science Society of America, Madison, WI, United States
References: 26
Accession Number: 2005-061712
Categories: Environmental geologyHydrochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Accessed on January 6, 2005
Illustration Description: illus. incl. 1 table, sketch map
Source Medium: WWW
N46°25'00" - N46°25'00", W119°45'00" - W119°45'00"
Secondary Affiliation: University of California at Berkeley, USA, United StatesPacific Northwest National Laboratory,
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200521
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