摘要:

Two independent techniques, X ray absorption and light transmission, are developed and demonstrated for imaging transient saturation fields in thin‐slab porous systems. The techniques yield full two‐dimensional saturation fields with high spatial and temporal resolution. In the time required to make a single measurement by one of the traditional methods (e.g., gravimetric or gamma densitometry) an entire image consisting of hundreds of thousands of points is acquired by either the X ray or light technique. These methods are also very sensitive, capable of resolving a hundred or more levels of saturation at each of these points. Evaluation of these techniques is accomplished by direct comparison of X ray and light data as well as comparison with gravimetric and gamma densitometry data. Results of the comparison show very close agreement between the four techniques (on average within 5% saturation). These techniques represent useful tools for investigating processes governing unsaturated flow and transport through porous me

ISSN:0043-1397    

DOI:10.1029/94WR00953

年代:1994

数据来源: WILEY

摘要:

This study presents an analysis of the rate of dilution of a conservative nonreactive tracer in two well‐known field experiments: The Borden (Ontario, Canada) experiment and the Cape Cod (Massachusetts) experiment. In evaluating the dilution of injected sodium bromide, in addition to computing the second spatial moments, we have used the dilution index and the reactor ratio. The dilution index is a measure of the formation volume occupied by the solute plume, and the reactor ratio is a shape factor, which measures how stretched and deformed the plume is. Unlike the second moments, which may go up or down during an experiment, the dilution index should increase monotonically. The results for both plumes were quite similar. After an initial period the dilution index increased linearly with time, which is macroscopically equivalent to transport in two‐dimensional uniform flow. The reactor ratio was relatively constant during the period of the experiments. Their values, about 0.72 for the Borden test and 0.63 for the Cape Cod test, indicate that the Cape Cod plume was more stretched and deformed than the Borden plume. The maximum concentration, which is an alternative to the dilution index for quantifying dilution, was found to be more erratic and more susceptible to sampling er

ISSN:0043-1397    

DOI:10.1029/94WR01983

年代:1994

数据来源: WILEY

摘要:

The two‐region model was developed originally to describe nonsorbing chemical transport in soils with dead‐end pores based on the concept of mobile and immobile regions in the soil. It has been shown that the model can simulate solute transport in soils with local stratification, or inhomogeneity, of hydraulic conductivity. However, the physical basis of the model becomes questionable, since the mobile‐immobile region concept does not apply in stratified soils. In both soil types the nonequilibrium effect is caused by an apparent mass transfer process within the soil, as distinct from advection and diffusion. Where there are immobile regions, the mass transfer is due to solute interregion diffusion alone. In stratified soils the nonequilibrium mass transfer process is affected also by local flow variations. A conceptual model, numerical simulations, and laboratory experiments are presented to analyze these effects. For a given soil with fixed local stratification of hydraulic conductivity, it is shown that in the low‐velocity range, the apparent mass transfer rate parameter, α, scales asV2/D(Vis pore water velocity in the two‐region model andDis the longitudinal dispersion coefficient), which implies that the mass transfer process is predominantly affected by local flow variations. When the velocity is relatively high, α ∝DT/h2(DTis the interregion diffusion coefficient andhis the characteristic thickness of the stratified layers) and the mass transfer process is dominated by interregion diffusion. These scaling relations for α reflect the two mechanisms controlling the mass transfer process in locally stratified soils. They have implications for scaling of time‐dependent mass transfer from laboratory models to prototype soils. In particular, the relationship α ∝V2/Dleads to the conclusion that exact physical modeling of nonsorbing chemical transport coupled with apparent mass transfer in locally stratified

ISSN:0043-1397    

DOI:10.1029/94WR01218

年代:1994

数据来源: WILEY

摘要:

This paper describes an investigation of flow and transport phenomena in heterogeneous, nonstationary formations, where the log conductivity is the superposition of a linear trend and a stationary fluctuation. The problem of flow and transport in a steady, two‐dimensional flow without recharge is investigated analytically for an infinite flow domain. General results are obtained for any space dimensionality, but applications were limited to the case of two‐dimensional flow in the horizontal plane. The log conductivity field is assumed to have a linear trend. We limited the scope of this study to the cases where the trend is either parallel or normal to the head gradient and to small variance in the log conductivity. This paper presents results for the moments of the velocity and the hydraulic head, the effective conductivity, macrodispersion coefficients, solute mass breakthrough curves, and travel time distributions, all in terms of the parameters of the log conductivity field and the boundary conditions. The effects of the trend in the conductivity on these results are analyzed and compared with those obtained when the apparent trend is neglected. The results may be used for predicting transport phenomena extending over distances of many integral scales, as well as for interpretation of field data where the presence of a trend is suspec

ISSN:0043-1397    

DOI:10.1029/94WR01950

年代:1994

数据来源: WILEY

摘要:

This paper presents a new Eulerian‐Lagrangian method for modeling flow and transport of passive solutes in heterogeneous porous formations. The physically plausible random velocity fields are generated by a geostatistical based model. The ability of the method to correctly reproduce the velocity field statistics and to satisfy mass balance is tested and demonstrated for the case of two‐dimensional flow. The method is found particularly useful in dealing with large fields where numerical, fixed grid methods such as finite difference or finite elements become very demanding from a computational point of view. The transport problem is solved in a Lagrangian framework by the particle‐tracking approach which uses a suitable grid refinement to correctly handle the velocity fluctuation at any a priori defined resolution. The new method is employed to compute the probability distribution functions of the concentration and travel times and to investigate the limitations of existing methods for predicting concentra

ISSN:0043-1397    

DOI:10.1029/94WR01489

年代:1994

数据来源: WILEY

摘要:

The hydraulic properties of an unsaturated homogenous and isotropic soil can be obtained from the unconfined flux out of a disc infiltrometer into the soil over the depth of wetting. The disc infiltrometer is becoming increasingly popular, but methods of analysis have generally relied on the restrictive assumptions of one‐dimensional flow at early times or quasi‐steady state flow at large times. We provide an approximate analytical expression for three‐dimensional unsteady, unconfined flow out of a disc infiltrometer, and this includes the geometric effect of the circular source but ignores gravity. This physically based solution is tested against data obtained from laboratory experiments on repacked material. The results illustrate that the difference between three‐dimensional and one‐dimensional flow is linear

ISSN:0043-1397    

DOI:10.1029/94WR01787

年代:1994

数据来源: WILEY

摘要:

In situ measurement of soil hydraulic properties may be achieved by analyzing the unconfined efflux from disc tension infiltrometers, once consistent infiltration equations can be derived. In this paper an analytical, three‐dimensional infiltration equation is developed, based on the use of parameters with sound physical meaning and adjustable for varying initial and boundary conditions. The equation is valid over the entire time range. For practical purposes, a simplified solution is also derived. The full and simplified equations give excellent agreement with published experimental results and are particularly useful for determining soil hydraulic properties through application of inverse procedure

ISSN:0043-1397    

DOI:10.1029/94WR01788

年代:1994

数据来源: WILEY

摘要:

We present a convective description of acid‐base transport in porous media which is based on classical one‐component nonlinear Chromatographic theory applied to the acidity of the system. In the mobile phase the solution acidity is given byc= [H+]t‐ [OH−]t, where [H+]tand [OH−]tare the total solution concentrations of H+and OH−, respectively. In the stationary phase the surface acidity corresponds to the charge density σ, which is commonly presented as a function ofpH of the solution. The response of a Chromatographic column to a steppH change at column inlet results in apH breakthrough curve which consists of a combined Chromatographic front. This combined front begins with a diffuse subfront and ends with a self‐sharpening subfront. The present Chromatographic theory is used to predict experimentally observedpH breakthrough curves for columns filled with materials of knownpH‐dependent charging behavior. Good agreement between theoretical predictions and experimental results is observed. Essentially, the same Chromatographic theory is used to explainpH breakthrough curves when the salinity of the input solution is changed. This situation leads usually to an additional nonretarded front where a ch

ISSN:0043-1397    

DOI:10.1029/94WR01785

年代:1994

数据来源: WILEY

摘要:

A semianalytical solution is presented to a mathematical model describing the flow of groundwater in response to a slug test in a confined or unconfined porous formation. The model incorporates the effects of partial penetration, anisotropy, finiteradius well skins, and upper and lower boundaries of either a constant‐head or an impermeable form. This model is employed to investigate the error that is introduced into hydraulic conductivity estimates through use of currently accepted practices (i.e., Hvorslev, 1951; Cooper et al., 1967) for the analysis of slug‐test response data. The magnitude of the error arising in a variety of commonly faced field configurations is the basis for practical guidelines for the analysis of slug‐test data that can be utilized by field practiti

ISSN:0043-1397    

DOI:10.1029/94WR01670

年代:1994

数据来源: WILEY

摘要:

Surfactant‐enhanced aquifer remediation (SEAR) is currently under active investigation as one of the most promising alternatives to conventional pump‐and‐treat remediation for aquifers contaminated by dense nonaqueous phase organic liquids. An existing three‐dimensional finite‐difference enhanced oil recovery simulator is adapted to model the SEAR process. This simulator incorporates the complex chemistry and multiphase transport behavior of surfactant/water/organic mixtures in permeable media. Model governing equations and parameter requirements are discussed, and simulations are employed to illustrate some important issues potentially affecting SEAR performance at the field scale. Simulations suggest that the total time for remediation could be reduced by more than an order of magnitude over conventional remediation approaches by employing SEAR. The assumptions, approximations, and conditions required to achieve such a favorable result are identified, and the importance of modeling as a quantitative tool for the assessment of SEAR is hi

ISSN:0043-1397    

DOI:10.1029/94WR01458

年代:1994

数据来源: WILEY