Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1988. / Includes bibliographical references (leaves 136-140).

Recent years have seen increasing use of atmospheric radionuclides for dating and tracing hydrogeologic processes. Hydrologists often assume that meteoric sources of these nuclides are dominant in ground water and that age-dating methods are limited primarily by analytical detection capability. However, in some cases, subsurface production may also limit the usefulness of these nuclides for dating. Equilibrium radionuclide concentrations are calculated as a function of depth for a variety of rock types. Production mechanisms include fissioning of heavy radionuclides; spallation by cosmic-ray nucleons; capture of neutrons, a-particles, muons and protons; and photonuclear reactions. Calculations indicate that deep subsurface production of ³H, ¹⁴c, ⁸⁵Kr and ⁹⁹Tc is generally below detection but that deep production of ³⁶C1, ³⁹Ar, ⁸¹Kr and ¹²⁹I establishes limits to age-dating of water in most rocks. Parameters for estimating production of ¹⁰Be, ²²Na, ²⁶Al, ³⁷Ar, ³²Si, ⁴¹Ca and ⁷⁹Se are included in appendices. Evidence for in-situ production of ³⁶C1 and ¹²⁹I is presented for two field studies. Concentrations in ground water from the Stripa granite, Sweden, were determined by accelerator mass spectrometry. ¹²⁹I values range from 1,000 to 200,000 atoms/ml, compared to an estimated background concentration in pre-1945 water of 20 atoms/ml. The high levels are attributed to production by spontaneous fission of ²³⁸U in the granite (44 ppm U). ³⁶C1/C1 ratios range from 50-200 x 10 -15 compared to about 40 x 10⁻¹⁵ in meteoric recharge. An increase in ratios with depth has been attributed to production of ³⁶C1 by neutron- capture on ³⁵C1 and is used to set upper limits on the residence time of water in the granite. The validity of using ³⁶C1/C1 ratios as a monitor of deep lithospheric neutron fluxes was tested by measuring the ratios in Cl extracted from Stripa granite. The average ratio, 190 x 10⁻¹⁵, agrees with ratios calculated based on rock chemistry, 190 x 10⁻¹⁵, and on the measured neutron flux, 220 x 10⁻¹⁵. ¹²⁹I and ³⁸C1 were also measured in uranium ores from the Koongarra and Ranger deposits, N.T., Australia. Samples from the oxidized ore zone contain only 6-23% of the ¹²⁹I contents predicted for equilibrium, suggesting preferential loss of ¹²⁹I relative to U during weathering. ³⁶C1 is produced as a result of high neutron fluxes in the ore. Measured ³⁶C1/C1 ratios range from 3 x 10 -12 to 1 x 10⁻¹⁰, corresponding to apparent neutron fluxes of 2 x 10⁵ to 1 x 10⁷/cm²/yr.

Thesis (M.S.)--Baylor University, 2005. / Includes bibliographical references (p. 48-50).

Thesis (M.S. - Hydorology and Water Resources)--University of Arizona, 1985. / Includes bibliographical references (leaves 65-67).

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1987. / Includes bibliographical references (leaves 137-141).

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 112-119).

Thesis (Ph. D.)--Memorial University of Newfoundland, 1997. / Blbliography: leaves 223-235. Also available online.

Carbon-14 was measured in the dissolved organic carbon (DOC) in ground water and compared with ¹⁴C analyses of dissolved inorganic carbon (DIC). Two field sites were used for this study; the Stripa mine in central Sweden, and the Milk River Aquifer in southern Alberta, Canada. The Stripa mine consists of a Precambrian granite dominated by fracture flow, while the Milk River Aquifer is a Cretaceous sandstone aquifer characterized by porous flow. At both field sites, ¹⁴C analyses of the DOC provide additional information on the ground-water age. At the Stripa site the DIC from the recharge area probably precipitates at around the 300 m level of the mine, never reaching the deeper ground waters. In this case, ¹⁴C analyses of the DOC provides a better estimate of the ground-water age. The dilution of the DIC by carbonates and microbial processes in the Milk River Aquifer is so great that geochemical corrections of ¹⁴C data are difficult. This is another example where ¹⁴C analyses of the DOC provide more information on ground-water age. Carbon-14 was measured on both the hydrophobic and hydrophilic organic fractions of the DOC. At the Stripa site, the hydrophobic organic compounds in the V2 borehole ranged from 7,500 to 15,500 years before present, suggesting a young component of ground water. Other hydraulic and isotopic evidence supports relatively recent ground water mixing with older brines in this borehole. The δ¹³C values of the DIC in the V2 borehole are light and similar to the stable carbon isotope values for the DOC, supporting a biogenic origin of the DIC. The organic compounds in the hydrophobic and hydrophilic fractions were also characterized. The DOC may originate from kerogen in the aquifer matrix, from soil organic matter in the recharge zone, or from a combination of these two sources. Carbon-14 analyses, along with characterization of the organics, were used to determine this origin. Carbon-14 analyses of the hydrophobic fraction in the Milk River Aquifer suggest a soil origin, while ¹⁴C analyses of the hydrophilic fraction suggest an origin within the Cretaceous sediments (kerogen) or from the shale in contact with the aquifer.

Theoretical and experimental studies of the chemical and physical factors which affect molecular diffusion of dissolved substances from fractures into a tuffaceous rock matrix have been made on rocks from G Tunnel and Yucca Mountain at the Nevada Test Site (NT8). Although a number of physical/chemical processes may cause nonadvective transport of dissolved species from fractures into the tuff matrix, diffusion in these rocks is controlled by the composition of the groundwater through multicomponent effects and several rock properties. The effective molecular diffusion coefficient of a particular species in the tuff can be related to its free aqueous diffusion coefficient by Dₑ = θ(m)(α/τ²)D₀ where bm is matrix porosity, α is the constrictivity, and τ is the tortuosity. The porosities of the samples studied ranged from 0.1 to 0.4. The parameter (α/τ²) ranged from 0.1 to 0.3, and effective matrix dif— fusion coefficients were measured to be between 2 to 17. x 10⁻⁷ cm²/s for sodium halides and sodium pentafluorobenzoate. Total porosity was found to be the principle factor accounting for the variation in effective diffusion coefficients. The constrictivity— tortuosity factor was found to have a fair correlation with the median pore diameters measured by mercury intrusion. Measurements of bulk rock electrical impedance changes with frequency indicate that the constrictivity factor, a, has a maximum value of 0.8 to 1, but may be smaller. If the larger values are correct, then the diffusion paths in tuff are more tortuous than in granular media. The diffusion coefficient matrix computed for various tracers in J-13 well water from the NTS indicates coupling of the diffusion fluxes of all ionic species. Multicomponent diffusion is a second order effect, however, which does not significantly affect experimental results. The results of a bench—scale fracture flow experiment revealed that the transport of ionic tracers (SCN ⁻ and pentafluorobenzoate) was affected by diffusion into the tuff matrix. The transport of a particulate tracer did not appear to be affected by diffusion.

Thesis (Ph. D. - Hydrology and Water Resources)--University of Arizona, 1985. / Includes bibliographical references (leaves 182-187).