Insitu Determination of Hydraulic Conductivity in the Vadose Zone Using Borehole Infiltration Tests
Predicting the rate of water movement above a water table is a crucial problem in hazardous and radioactive waste disposal, in the design of dams, and in the irrigation and drainage of agricultural land. Hydraulic conductivity, the key soil characteristic governing the rate of water movement, was determined in the field using constant head borehole infiltration tests.
Earlier results of numerical simulations of the saturated-unsaturated flow process were verified; these indicate that only a finite zone of soil immediately surrounding the borehole is nearly saturated. Carbon dioxide injected into the borehole prior to water infiltration is an effective means to reduce the amount of entrapped air and reduce the water volume required to complete a test. New empirical solutions were developed to account for capillary effects. The borehole test results generally compared favorably with other field techniques that are restricted in application to near surface, and also with laboratory permeameter experiments on shelby tube samples. Laboratory permeameter experiments on small ring samples (100cc) produced consistently greater values of saturated hydraulic conductivity than other methods.