摘要:

ABSTRACT:This paper presents criteria for establishing the identification status of the inverse problem for confined aquifer flow. Three linear estimation methods (ordinary least squares, two‐stage least squares, and three‐stage least squares) and one nonlinear method (maximum likelihood) are used to estimate the matrices of parameters embedded in the partial differential equation characterizing confined flow. Computational experience indicates several advantages of maximum likelihood over the linear meth

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:The usefulness of stochastic models in describing the spatial variability of hydrogeologic quantities, such as permeability, storativity, piezometric head, seepage velocity, and solute concentrations is now widely recognized. In practice, these quantities are represented as the sum of a well‐structured component, or drift, and a more erratic fluctuation component which is described statistically through its covariance function. This paper reviews some of the most recent and most promising methods for the estimation of parameters of these covariances from existing data. They are maximum likelihood, restricted maximum likelihood, minimum‐variance unbiased quadratic estimation, and minimum‐norm (weighted least squares) estimation. The applicability of such methods to conditional and unconditional probability problems is disc

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00832.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:This paper presents a method for estimating aquifer dispersivities in solute transport models. Sensitivity equations are derived for the calculation of sensitivity coefficients. A modified Gauss‐Newton algorithm is used to perform the least‐squares minimization. A statistical procedure is outlined to assess reliability of the estimated parameters. The solute transport model is solved by the upstream weighted, multiple cell balance method which combines the concepts of local mass balance and finite element approximations. A one‐dimensional solute transport problem in a vertical column system is first used to illustrate the inverse technique. A second example considers the parameter identification problem for three‐dimensional solute transport with a unidirectional steady and uniform flow field. The third example solves the parameter identification problem in a three‐dimensional, stream‐aquifer, solute transport system with steady state flow. Numerical experiments are conducted to study data requirements for parameter ide

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:A method is derived to efficiently compute nonlinear confidence and prediction intervals on any function of parameters derived as output from a mathematical model of a physical system. The method is applied to the problem of obtaining confidence and prediction intervals for manually‐calibrated ground‐water flow models. To obtain confidence and prediction intervals resulting from uncertainties in parameters, the calibrated model and information on extreme ranges and ordering of the model parameters within one or more independent groups are required. If random errors in the dependent variable are present in addition to uncertainties in parameters, then calculation of prediction intervals also requires information on the extreme range of error expected. A simple Monte Carlo method is used to compute the quantiles necessary to establish probability levels for the confidence and prediction intervals. Application of the method to a hypothetical example showed that includsion of random errors in the dependent variable in addition to uncertainties in parameters can considerably widen the prediction interv

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00834.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:Recent literature concerning the modeling of chemical reactions during transport in ground water is examined with emphasis on sorption reactions. The theory of transport and reactions in porous media has been well documented. Numerous equations have been developed from this theory, to provide both continuous and sequential or multistep models, with the water phase considered for both mobile and immobile phases. Chemical reactions can be either equilibrium or non‐equilibrium, and can be quantified in linear or non‐linear mathematical forms. Non‐equilibrium reactions can be separated into kinetic and diffusional rate‐limiting mechanisms. Solutions to the equations are available by either analytical expressions or numerical techniques. Saturated and unsaturated batch, column, and field studies are discussed with one‐dimensional, laboratory‐column experiments predominating. A summary t able is presented that references the various kinds of models studied and their applications in predicting chemical concentrations in gr

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:A key parameter in modeling two‐phase flow phenomena is relative permeability. It is important to understand which variables influence relative permeability, especially since so few measurements of relative permeability have been made for typical contaminants at hazardous waste sites. This paper focuses on the effect of five variables on relative permeability: intrinsic permeability, pore‐size distribution, viscosity ratio, interfacial tension, and wettability, by critically reviewing previously published relative permeability experiments. The wide variability in the functional relationship between relative permeability and saturation should be considered in attempts to model two‐phase

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:A three well injection‐production test was performed at the United Creosoting Company (UCC) site in Conroe, Texas, to estimate the effective in situ retardation factors for adsorption and to evaluate the significance of biotransformation in limiting the transport of polycydic aromatics present in the shallow aquifer. The field test was also used as a model to determine if this type of testing would be feasible at other hazardous waste sites. During the test, chloride, a non‐reactive tracer and two organic compounds, naphthalene and paradichlorobenzene (pDCB), were injected into a center well for 24 hours followed by clean ground water for six days. Ground water was continuously produced from two adjoining wells and monitored to observe the breakthrough of these compounds. Data from the test were analyzed by comparing the statistical moments of the chloride and organics distributions. Retardation factors for naphthalene and pDCB were estimated to be 1.03 and 0.97 by comparison of the statistical moments. A significant loss of naphthalene and pDCB was also observed during the three well test, apparently due to biotransformation. These results suggest that biotransformation is the major process limiting the transport of naphthalene and similar compounds at the UCC s

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:This paper explores some of the advances of the boundary element method, as applied to ground‐water problems, during the last five years. Although the method is still somewhat limited compared to solution by finite elements, the range of solutions has increased considerably. Diffusion and advection‐diffusion solutions are done efficiently. These include the incorporation of inhomogeneity, anisotropy, and nonlinear diffusion. The difficult problem of stream‐aquifer interaction is an important application as it is much easier to follow a free surface with its multiple configurations. The application must be able to cycle between ground‐water connection and disconnection with the stream and include seepage surfaces. Flow in fractured media is a natural application where the flow in fractures can usually be treated without a computational exception in spite of extremely high aspect ratios. The case of seawater intrusion forms a type of free surface problem and thus is a case for which the method has special advantages. For these and other applications the boundary element method provides an inexpensive technique for calculation where the data preparation and setup time is minimal. In most of these cases, programs can and have been written on microco

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:A major concern in managing water resources is whether or not water quality variables have changed over time or space. The two‐sample Student's t‐test is probably the most commonly used statistical test for this purpose. Given that the underlying assumptions of the test may often be violated by water quality variables, a major concern regarding applicability of the test arises. This paper reviews and synthesizes available information in order to examine the effects of non‐normality, unequal variances, serial dependence, and seasonality on the performance of the two‐sample t‐test. The results suggest the t‐test is robust for non‐normal distributions if the distributions have the same shape (either symmetric or skewed) and sample sizes are equal. The t‐test is also robust for unequal variances if the sample sizes are equal. The t‐test appears not to be robust when: 1) samples come from two distributions of different shape, 2) samples have unequal variances and unequal sample sizes, 3) serial dependence in observations is present, or 4) seasonal changes, in concentration are presen

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACT:The accumulation of arsenic, nickel, copper, and lead in the soil profile was determined beneath five urban storm‐water retention/recharge basins used by the Fresno Metropolitan Flood Control District, California. Soils were sampled from the surface to the first zone of saturation and compared with soils from an adjacent un‐contaminated control site. These elements were found to be accumulating in the first few centimeters of basin soil and are important to the effectiveness of a specific best management practice, i.e., the retention and recharge of urban storm water. Study basins in use since 1962, 1965, and 1969 had lead contents in the 0–2 cm soil depth interval‘of 570, 670, and 1400 mg Pb/kg soil, respectively. The median indigenous soil lead concentration was 4.6 mg/kg soil. The practice of removing excess flood runoff water from two basins by pumping apparently is a factor in reducing the accumulation rate of these elements in the surface soils of the

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1987.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY