The hydraulic conductivity (K) variation has important ramifications for ground water flow and the transport of contaminants in ground water. The delineation of the nature of that variation can be critical to complete characterization of a site and the planning of effective and efficient remedial measures. Site-specific features (such as high-conductivity zones) need to be quantified. Our alluvial field site in the Kansas River valley exhibits spatial variability, very high conductivities, and nonlinear behavior for slug tests in the sand and gravel aquifer. High-resolution, multilevel slug tests have been performed in a number of wells that are fully screened. A general nonlinear model based on the Navier-Stokes equation, nonlinear frictional loss, non-Darcian flow, acceleration effects, radius changes in the wellbore, and a Hvorslev model for the aquifer has been used to analyze the data, employing an automated processing system that runs within the Excel spreadsheet program. It is concluded that slug tests can provide the necessary data to identify the nature of both horizontal and vertical K variation in an aquifer and that improved delineation or higher resolution of K structure is possible with shorter test intervals. The gradation into zones of higher conductivity is sharper than seen previously, and the maximum conductivity observed is greater than previously measured. However, data from this project indicate that well development, the presence of fines, and the antecedent history of the well are important interrelated factors in regard to slug-test response and can prevent obtaining consistent results in some cases.

High-resolution slug testing.

Effects of free convection and friction on heat-pulse flowmeter measurement

In the authors' opinion, the ability of hydrologists to perform field measurements of aquifer hydraulic properties must be enhanced if they are to improve significantly the capacity to solve ground water contamination problems at Superfund and other sites. Therefore, the primary purpose of the report is to provide motivation and new methodology for measuring K(z), the distribution of horizontal hydraulic conductivity in the vertical direction in the vicinity of a test well. Measurements in nearby wells can then be used to build up three-dimensional distributions. For completeness, and to enhance the usefulness of the report as a field manual, existing methodology for the measurement of effective porosity, vertical hydraulic conductivity, storativity and hydraulic head, are presented also. It is argued that dispersion-dominated models, particularly two-dimensional, vertically-averaged (areal) models, have been pushed about as far as they can go, and that two-dimensional vertical profile or fully three-dimensional advection-dominated transport models are necessary if they are to increase significantly the ability to understand and predict contaminant transport, reaction, and degradation in the field. Such models require the measurement of hydraulic conductivity distributions, K(z), rather than vertically averaged values in the form of transmissivities.

O. Guven

Papers

New approach and methodologies for characterizing the hydrogeologic properties of aquifers. Final report, August-December 1989