Estimation of the Electrokinetic Coupling Coefficient and Hydraulic Conductivity from Streaming Potential Measurements in a Falling-Head Permeameter

Measurement of streaming potentials associated with groundwater flow has emerged as a viableand innovative hydrogeophysics tool for hydrologic characterization of the subsurface as it allowsfor non-invasive and spatially dense grids for system state measurements. We present results ofstreaming potential (SP) measurements collected from experiments performed in a falling-headpermeameter with the objective of evaluating its suitability for measuring hydraulic conductivity(K) and the electrokinetic coupling coefficient (C) of sediments or crushed rock. TraditionallySP and head data collected in a constant-head permeameter are used for estimating the couplingcoefficient as C = slope based on its definition C = d(SP)/d(head). In this work, we plotted SP againsthead data collected at the same times in the falling-head permeameter. We compare K estimatedfrom SP data to that estimated from hydraulic head data. The estimation of C and K from SPdata is accomplished through a semi-empirical model based on the classical lumped-parametermodel [Fetter(2001)] that is traditionally used for analysing hydraulic head data collected infalling-head permeameters. The semi-empirical model has an additional exponential-decay termto account for post-flow relaxation of system state observed in the SP response. The value of Kestimated from transient SP data (K = 17.7 m/d) is practically the same as that obtained fromhead data (K = 17.9 m/d). The estimated electrokinetic coupling coefficient (C = 93.0 mV/m)is about 10% smaller than that obtained by the traditional method (C = 102.3 mV/m). Forpractical purposes, one can state, with a measure of confidence, that transient SP data from afalling-head permeameter can be used to estimate K and C.