摘要:

In accordance with recommendations by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry [IUPAC, 1994;Coplen, 1994],Water Resources Researchrequests that authors (in all cases where feasible) (1) discontinue reporting isotopic abundances relative to SMOW (standard mean ocean water) and PDB (Peedee belemnite), (2) express hydrogen isotopic ratios of all substances relative to VSMOW (Vienna standard mean ocean water) on a normalized scale such that the δ2H of SLAP (standard light antarctic precipitation) relative to VSMOW is −428‰, (3) express carbon isotopic ratios of all substances relative to VPDB (Vienna Peedee belemnite) on a scale defined by adopting a δ13C value of +l.95‰ for NBS 19 carbonate relative to VPDB, (4) express oxygen isotopic ratios relative to either VSMOW or VPDB on a normalized scale such that the δ18O of SLAP is −55‰ relative to VSMOW, and (5) indicate values of isotopic fractionation factors if isotopic abundances of a mineral or compound depend upon s

ISSN:0043-1397    

DOI:10.1029/95WR02430

年代:1995

数据来源: WILEY

摘要:

Leaky faults provide important flow paths for fluids to move underground. It is often necessary to characterize such faults in engineering projects such as deep well injection of waste liquids, underground natural gas storage, and radioactive waste isolation. To provide this characterization, analytical solutions are presented for groundwater flow through saturated aquifer‐fault‐aquifer systems assuming that both the aquifers and the fault are homogeneous and that the fault has an insignificant effect on aquifer hydraulic properties. Three different conditions are considered: (1) drawdown in the unpumped aquifer is negligibly small; (2) drawdown in the unpumped aquifer is significant, and the two aquifers have the same diffusivity; and (3) drawdown in the unpumped aquifer is significant, and the two aquifers have different diffusivities. Methods are presented to determine the fault transmissivity from pumping test d

ISSN:0043-1397    

DOI:10.1029/95WR02483

年代:1995

数据来源: WILEY

摘要:

Fluid electrical conductivity logging experiments introduced byTsang et al.[1990] represent a new technology for studying the hydraulic properties of discrete fractures in open boreholes. These experiments consist of replacing water in the well bore with deionized water and then pumping the well to induce formation water to return to the well bore. During and after the fluid exchange the entire well is logged to measure fluid electrical conductivity (FEC). At locations where formation water enters the well there are abrupt increases in the borehole FEC, thereby revealing the location of hydraulically conductive fractures. As pumping continues, high FEC water moves up the well bore at a rate proportional to the total inflow rate below the observation point. Inflow rates and FECs of formation water associated with each fracture can be inferred by modeling the FEC profiles with the one‐dimensional advective dispersion equation. In this paper I present an inverse model which estimates the inflow rates and formation FEC values that optimally fit observed FEC logs acquired during fluid exchange experiments described byTsang et al.[1990]. With this inverse model, inflow rates are constrained by the rate at which the well is pumped during the experiment. The forward model is solved numerically using a control volume finite difference scheme with power law upstream weighting and source term linearization. The inverse problem is solved using the Gauss‐Newton iterative method. The rows of the Jacobian matrix, or the sensitivity coefficients, are calculated numerically with the same algorithm that solves the forward problem. Both constrained and unconstrained inverse models are used to interpret fluid logging experiments performed in research wells penetrating Piedmont rocks of North Carol

ISSN:0043-1397    

DOI:10.1029/95WR02482

年代:1995

数据来源: WILEY

摘要:

Time domain reflectometry (TDR) offers a unique opportunity to measure liquid water contentθLin frozen soil, since the permittivity of ice is much lower than that of water. However, calibrations of TDR derived from drying unfrozen soil, where water is replaced by air, may not apply to a freezing soil, where water is replaced by ice, since the permittivity of ice is greater than that of air. We designed a gas dilatometer to calibrate TDR forθLin frozen soil. A soil sample is hermetically sealed in the gas dilatometer; subsequent soil freezing reduces total air space and hence increases pressure inside the gas dilatometer, since ice is less dense than water. The amounts of soil water frozen were computed from measured pressure change as temperature was incrementally decreased. TDR calibrations for two samples of the same soil at different total water contents had identical slopes but different intercepts, supporting our hypothesis that there exists no unique calibration of TDR forθLfor frozen soil, but rather a family of calibration curves, each curve corresponding to a different total water conte

ISSN:0043-1397    

DOI:10.1029/95WR02769

年代:1995

数据来源: WILEY

摘要:

To study relationships between soil hydraulic properties and soil structural properties, a computer micro model of soil is constructed. We present first a general method of building a two‐dimensional porous structure, including both pores and particles, with different levels of aggregation resulting from a fragmentation process. A fractal structure is obtained when self similarity is imposed over the successive scales of fragmentation. Emphasis is put upon the modeling of the retention curve. A classical capillary model and methods taken from percolation theory enable us to simulate qualitatively the primary and secondary loops of this hysteretic curve. In the fractal case, theoretical analytical expressions proposed for adjusting retention data are tested. The unsaturated hydraulic conductivity is also calculated on the same simulated soil by analogy with an electrical network. The soil structures are deformable and simulation proves to be a useful tool to investigate the behavior of swelling soil

ISSN:0043-1397    

DOI:10.1029/95WR02214

年代:1995

数据来源: WILEY

摘要:

A two‐dimensional numerical model is developed that incorporates the mechanism of colloid‐facilitated transport in discretely fractured porous media. The numerical model accounts for aqueous phase contaminant transport in the fractures and the porous matrix, colloid transport in the fractures, and sorption of the solute. Deep‐bed filtration of the colloids is accounted for, and the solute is allowed to sorb on both the mobile and filtered colloids. The numerical formulation allows for either equilibrium or kinetic sorption reactions onto the fracture walls, the matrix solids, and the mobile and filtered colloids according to either a Langmuir or a Freundlich isotherm. The results of a series of simulations involving a system of parallel fractures explore the importance of mobile colloids on contaminant migration and indicate that if sorption onto the colloids is a slow kinetic process, then the mobile colloids may lead to significantly enhanced contaminant migr

ISSN:0043-1397    

DOI:10.1029/95WR02180

年代:1995

数据来源: WILEY

摘要:

Numerical simulations of colloid‐facilitated contaminant transport in fractured porous media were performed to examine the influence of mobile colloids on contaminant migration through a network of fractures. Simulations involving transport through fracture networks in a clay and a sandstone rock indicate that colloid‐facilitated contaminant transport can be an important factor leading to the rapid exceedance of water quality standards at large distances from the contaminant source. If the colloids are highly mobile in open fractures and there is a strong affinity for a reactive contaminant to remain adsorbed onto them, then low but environmentally significant contaminant concentration levels can quickly propagate through an interconnected network of fractures. The total concentration plumes that are produced are highly irregular in regions in advance of the zone of bulk aqueous phase contaminant transport. Because of this feature, colloid‐enhanced solute transport is likely to increase prediction uncertainty compared to the case when colloids are absent because field data on fracture network interconnectivity, aperture values, and values of parameters such as colloid filtration coefficients in the fractures are typically la

ISSN:0043-1397    

DOI:10.1029/95WR02181

年代:1995

数据来源: WILEY

摘要:

This study examines the influence of source release location, size, and strength on the infiltration rate and degree of lateral spreading of a dense nonwetting liquid infiltrating into an initially wetting liquid saturated, heterogeneous porous medium. It is demonstrated through numerical simulation in 25 realizations of a spatially correlated random hydraulic conductivity field that infiltration rates for point source releases are lognormally distributed with a variance equal to that of the underlying hydraulic conductivity distribution. The variability in infiltration rates is shown to decrease for sources larger than the correlation scale of hydraulic conductivity. In all cases, individual infiltration rates showed no tendency to converge to the ensemble average. A moment analysis demonstrates that the degree of lateral spreading of the nonwetting body for individual realizations varied greatly and also did not display a tendency to converge to an ensemble average. Numerical simulations carried out in an equivalent homogeneous porous medium incorporating large‐scale anisotropy of intrinsic permeability provided infiltration rates below the ensemble average. For point source releases the degree of lateral spreading exhibited in the equivalent homogeneous porous medium was below the entire ensemble of heterogeneous results. A series of 10 simulations conducted in a single realization demonstrates that the degree of lateral spreading (second moment) along main drainage is a function of the average nonwetting phase saturation with greater degrees of lateral spreading at low capillary pressures. The practical implication of this study is that in addition to fluid and media properties the specific order of encounter of varying permeability lenses must be known in the immediate vicinity of a nonwetting phase release if infiltration rates are to be accurately predicte

ISSN:0043-1397    

DOI:10.1029/95WR02329

年代:1995

数据来源: WILEY

摘要:

Groundwater flow through bounded rectangular aquifers is analyzed in a stochastic framework. New analytical expressions of the head covariance (and variance) and the log transmissivity head cross covariance are derived for the simplified first‐order problem. Effects of different boundary conditions, the aquifer size, and the log transmissivity correlation scale upon head moments are studied. The results are compared to analytical half‐plane solutions, demonstrating significant differences in several cases. Finally, the problem is solved numerically using the Monte Carlo simulation method. The realizations of the log transmissivity field are generated in two different ways. Through comparisons with the analytical results the accuracy of the numerical methods is shown to be excell

ISSN:0043-1397    

DOI:10.1029/95WR01956

年代:1995

数据来源: WILEY

摘要:

The integrodifferential equation for the spatial second momentsXof the ensemble mean concentration in a heterogeneous aquifer is nonlinear due to statistical dependence of the particle displacement onX. This nonlinear equation is either linearized or quasi‐linearized in previous studies to derive the linear and quasi‐linear theories of time‐dependent macrodispersion in aquifers. In this study a fully nonlinear analysis is carried out by solving the integrodifferential equation forXnumerically and iteratively. The effects of the variance of log hydraulic conductivities σY2, the local Péclet numberPe, and the anisotropic ratioeare then investigated. Results show that in both statistically isotropic and anisotropic media, as compared with the linear theories, the effect of nonlinearity inXis to reduce the spatial longitudinal variance,X11, and enhance the transverse spreading of a solute plume except in isotropic media with σY2≤ 1, where the linear theories may underestimate the longitudinal spreading of a solute. It is also shown that the effect of local dispersion onX11can be neglected whenPe≥ 10 but on the transverse macrodispersion, this effect is significant forPeas large as 100. Nevertheless, the effect ofPeon macrodispersion is secondary as compared with the effect of nonlinearity inX. Application of the nonlinear results shows good fits to the observed spatial variances of tracer concentration in the Borden experiment and excellent agreement with the simulated variances from recent Monte Carlo

ISSN:0043-1397    

DOI:10.1029/95WR02714

年代:1995

数据来源: WILEY