Determining the bulk saturated hydraulic conductivity of fractured low-permeable materials with a single well test

A thick sequence of matrix-dominated (composed of predominantly clay and silt-size particles) glacial diamicton covers extensive areas of the Midwest. Although generally characterized by a low hydraulic conductivity, the diamicton is often fractured. Hydraulic conductivity measurements on small samples, with a single piezometer or laboratory permeameter, underestimate the large scale or bulk hydraulic conductivity. Accurate measurements of hydraulic conductivity are important because the diamicton effectively controls recharge and the migration of contaminants to groundwater resources. The authors developed a single well test method for measuring hydraulic conductivity in areas where saturated diamicton can be excavated near the surface, in strip mines or quarries. A modified seepage meter (the well) was constructed from the end of a 56 cm diameter steel drum. It is installed in a 15 cm deep circular trench and sealed with bentonite. After 24 hours, water is added slowly through a 2.54 cm diameter vertical standpipe in the end of the steel drum, until a head of 64.5 cm above the ground surface is achieved. The water level in the standpipe is monitored through time with an on-site data logger connected to a transducer at the base of the drum. Test data are analyzed with a three-dimensionalmore » radial finite difference numeric model. This method tests an area over 2,463 sq cm, and the well can be installed directly over fractured areas, if desired. The authors continue to evaluate the distribution of hydraulic conductivity and its relation to fracture density.« less