John F. Pickens

An analytical solution for solute transport through fractured media with matrix diffusion

Abstract An analytical solution is presented for solute transport in a planar fracture coupled with diffusion into the adjacent matrix. The solution solves for the transient concentration distribution along the fracture as well as into the matrix. The mechanisms for solute transport are assumed to be advection in the fracture and diffusion in the porous matrix. The use of the analytical solution is illustrated by simulation of laboratory data from a column tracer test on fractured till and by simulation of a hypothetical scenario consisting of a single long continuous fracture in a regional groundwater flow system.

Application of a coupled adjoint sensitivity and kriging approach to calibrate a groundwater flow model

A new technique is employed to calibrate a regional-scale groundwater flow model to an extensive data base of undisturbed (i.e., assumed to be steady state) and transient heads. The methodology presented in this study is similar in concept to one presented by de Marsily et al. (1984) in that an adjoint sensitivity technique is coupled with a kriging algorithm to calibrate a flow model. The notable difference of the methodology presented in this paper is that it directly identifies the regions where modification of the models kriged transmissivity or boundary pressure values will directly improve the overall fit between measured and model-calculated heads at selected wells. At the locations identified as most sensitive to transmissivity changes, synthetic transmissivity values, referred to as pilot points, are added to the transmissivity data base and used as input for kriging the transmissivity field. An application of the methodology to data originating from approximately 10 years of regional hydrogeologic site characterization efforts that have been conducted in the Culebra dolomite at the Waste Isolation Pilot Plant in southeastern New Mexico is presented.

Finite-element analysis of the transport of water and solutes in title-drained soils

Abstract The finite-element method based on a Galerkin technique was used to formulate the problem of simulating the two-dimensional (cross-sectional) transient movement of water and solute in saturated or partially saturated nonuniform porous media. The numerical model utilizes linear triangular elements. Nonreactive, as well as reactive solutes whose behaviour can be described by a distribution coefficient or first-order reaction term were considered. The flow portion of the model was tested by comparison of the model results with experimental and finite-difference results for transient flow in an unsaturated sand column and the solute transport portion of the model was tested by comparison with analytical solution results. The model was applied to a hypothetical case involving movement of water and solutes in tile-drained soils. The simulation results showed the development of distinct solute leaching patterns in the soil as drainage proceeded. Although applied to a tile drainage problem in this study, the model should be equally useful in the study of a wide range of two-dimensional water and solute migration problems.