Carbon and isotopic mass balance models of Oasis Valley‐Fortymile Canyon Groundwater Basin, southern Nevada

Environmental isotopes and carbon chemistry provide means of differentiating various recharge areas, flow paths, and ages of ground water in portions of the Nevada Test Site and vicinity. Regional {delta}D/{delta}{sup 18}O trends are offset from the present-day meteoric line by a deuterium depletion of 5 per thousandth, suggesting paleoclimatic changes. Partial pressures of CO{sub 2} and the {sup 18}O and {sup 13}C data indicate solubility and isotopic equilibrium between the gas and water in the soil zone with progressive exchange with underlying ground water in the shallow alluvium of Oasis Valley. Application of a closed system CO{sub 2} model using the EQ3NR/EQ6 reaction path simulator successfully reproduces chemical compositions observed in the alluvium in the Amargosa Desert and in the deep tuff aquifer beneath Pahute Mesa and Yucca Mountain. Initial P/sub CO{sub 2}/ input to the soil zone during recharge was calculated to range from 0.03 to 0.10 atm, which is comparable to measured soil CO{sub 2} pressures in Oasis Valley. Results are compared for {sup 14}C ages using the {delta}{sup 13}C dilution correction and a mass action correction term relating predicted and calculated ionic activity products of CaCO{sub 3}. Results are generally comparable with discrepancies attributed to anomalous {delta}{supmore » 13}C values.« less

[1]  E. Weeks,et al.  Analysis of gaseous-phase stable and radioactive isotopes in the unsaturated zone, Yucca Mountain, Nevada , 1985 .

[2]  L. Benson,et al.  Chemical composition of ground water in the Yucca Mountain area, Nevada, 1971-84 , 1985 .

[3]  J. Kerrisk.  Reaction-path calculations of groundwater chemistry and mineral formation at Rainier Mesa, Nevada , 1983 .

[4]  J. Jouzel,et al.  Global Climatic Interpretation of the Deuterium-Oxygen 18 Relationship , 1979 .

[5]  T. J. Wolery,et al.  Calculation of chemical equilibrium between aqueous solution and minerals: the EQ3/6 software package. [In FORTRAN extended 4. 6 for CDC6600 and 7600] , 1979 .

[6]  R. Brown,et al.  The carbon isotope geochemistry of a small groundwater system in northeastern Ontario , 1978 .

[7]  L. Benson.  Fluctuation in the Level of Pluvial Lake Lahontan During the last 40,000 Years , 1978, Quaternary Research.

[8]  T. Wigley.  Carbon-14 dating of groundwater from closed and open systems , 1975 .

[9]  B. Hanshaw,et al.  Relationship between the carbon isotope composition of soil CO2 and dissolved carbonate species in groundwater , 1973 .

[10]  I. Friedman,et al.  Deuterium Content of Snow as an Index to Winter Climate in the Sierra Nevada Area , 1972, Science.

[11]  J. A. Kittrick.  Stability of Montmorillonites: II. Aberdeen Montmorillonite 1 , 1971 .

[12]  H. Helgeson,et al.  Evaluation of irreversible reactions in geochemical processes involving minerals and aqueous solutions - I. Thermodynamic relations , 1968 .

[13]  Claassen.  Sources and mechanisms of recharge for ground water in the west-central Amargosa Desert, Nevada: a geochemical interpretation. Hydrology of nuclear test sites , 1985 .

[14]  W. Mook.  Chapter 2 – CARBON-14 IN HYDROGEOLOGICAL STUDIES , 1980 .

[15]  A. White,et al.  The effect of dissolution of volcanic glass on the water chemistry in a tuffaceous aquifer, Rainier Mesa, Nevada , 1980 .

[16]  A. White.  Geochemistry of ground water associated with tuffaceous rocks, Oasis Valley, Nevada , 1979 .

[17]  J. R. O'neil,et al.  Compilation of stable isotope fractionation factors of geochemical interest , 1977 .

[18]  William Thordarson,et al.  Hydrogeologic and hydrochemical framework, south-central Great Basin, Nevada-California, with special reference to the Nevada Test Site , 1975 .

[19]  E. Wallick.  Isotopic and chemical considerations in radiocarbon dating of groundwater within the arid Tucson Basin, Arizona. , 1973 .

[20]  R. K. Blankennagel,et al.  Geohydrology of the eastern part of Pahute Mesa, Nevada Test Site, Nye County, Nevada , 1973 .

[21]  J. A. Kittrick.  Stability of Montmorillonites: I. Belle Fourche and Clay Spur Montmorillonites1 , 1971 .

[22]  Edwin Butt Eckel,et al.  Nevada test site , 1968 .