Using electrical resistivity logs and short duration pumping tests to estimate hydraulic conductivity profiles

Abstract

Hydraulic conductivity profiles (HCPs) are of crucial importance for 3-dimensional flow and transport groundwater models. Easy and inexpensive methods for the estimation of such profiles increase their availability and strengthen the efficiency of the models. In this study a method is presented, which combines the electrical resistivity (ER) measured over the depth of the aquifer in a borehole and the response of the aquifer to the short duration pumping from the borehole. The hydraulic conductivity profile is calculated from the Kozeny-Carman equation, in which the profiles of the porosity and the mean grain size (MGS) are required. Porosity is calculated from Archie’s law using the intrinsic formation factor, which results from the ER. MGS is calculated from the porosity using a relationship between them. The initial form of this relationship is obtained from literature data and is then adjusted to the conditions of each particular case. The adjustment is achieved by calibrating a MODFLOW based groundwater model, so that it sufficiently simulates the temporal variation of the water level measured in the borehole during the short pumping. The method is applied to the estimation of the HCP in an unconsolidated alluvial aquifer in Greece. The sensitivity of the results to the parameters and assumptions used in the method is investigated and discussed.