Permeability estimation from transient vadose zone pumping tests in shallow coastal-plain sediments

Abstract

Short-term, field-scale transient vadose zone pumping tests were performed on several wells at the Savannah River Site, located near Aiken, South Carolina. A total of 18 vacuum extraction tests were conducted in shallow coastal-plain vadose zone sediments, which yielded 38 data sets for analysis. Data collected during these tests were analyzed using two different modified Hantush-Jacob models to estimate the physical properties of the unsaturated sediments. The first model used was a commercially available software package used to estimate aquifer properties. This model assumed the test fluid (air) to be incompressible. The second model used was provided by Clemson University and accounted for the compressibility of the test fluid. This model was used primarily to provide confirmation of results from the first model. Comparisons between the results of the two models showed that both produced similar estimates of permeability for a given data set. Results from the analysis of the 38 data sets showed that the radial air permeability values ranged from 4.7 to 84.0 d. Vertical air permeability values were found to range from 0.93 to 11.7 d. The permeability values for the overlying semiconfining layer ranged from 2.7 1010 to 2.01 d. The results from these tests can be used to establish a general range of air permeabilities for shallow coastal-plain vadose zone sediments.