Hydraulic Conductivity At a Hazardous Waste Disposal Site: Comparison of Laboratory and Field-Determined Values

The hydraulic conductivity of fine-grained deposits from a waste disposal site in southern Illinois was determined by both laboratory and field tests. Laboratory tests on undisturbed and recompacted samples were performed in a Harvard-type miniature permeameter. Field methods included slug tests analysed by two different methods and recovery tests. Geometric means of hydraulic conductivity determined by the three field methods were similar for each of the geologic units tested. Most average laboratory-determined values were at least one order of magnitude lower than their field counterparts. Slug tests were also conducted on angle holes in an attempt to take into account vertical fractures. Average values from field tests of the angle holes were greater than for the vertical holes, thus leading to the tentative conclusion that the vertical fractures cause the hydraulic conductivity of material to be higher than that indicated by the results from the vertical holes. Results of this study indicate that field tests should be used as the primary method for determining hydraulic conductivity at waste disposal facilities. Laboratory tests should be used to supplement the field tests and provide information on the variability of each material type across the site.