Measuring hydraulic conductivity using streaming potentials (original) (raw)

Estimation of hydraulic parameters in heterogeneous aquifers require high resolution measurement of characteristic parameters to infer groundwater flow pattern. The common practice is to measure drawdown on few boreholes during pumping test. The information obtained from pumping test has limited spatial representation of hydraulic conductivity. A complementary, approach is to measure streaming potentials during pumping and recovery phases to provide additional spatially dense data. Streaming potential method is a passive, non-invasive geophysical approach and its signals are generated by groundwater flow through electro-kinetic coupling. Interpretation of streaming potential data in terms of groundwater flow parameters is facilitated by a coupled flow relationship which links streaming potential gradient to hydraulic gradient through a constant of proportionality called the electro-kinetic coupling coefficient. This paper demonstrates the applicability of estimating the hydraulic conductivity using streaming potentials in fractured and porous Karoo aquifers. Field experiments were conducted on the Campus and Krugersdrift test sites in Bloemfontein. The Campus test site is a fractured aquifer with hydraulic conductivity values between 1.1 to 2 m/d. Krugersdrift test site is a porous aquifer with hydraulic conductivity values between 9.9 to 11 m/d. The electro-kinetic coupling coefficient was determined by correlating streaming potentials near observation boreholes with the hydraulic head. Measured streaming potentials formed a positive anomaly around the pumping borehole, mirroring the hydraulic head cone of depression. Hydraulic conductivity values estimated from streaming potential field analytical solution for transient mode were in the same order as values determined through analytical analysis of drawdown data with relative error of 0.2. Key words: Passive geophysics, streaming potential, hydraulic conductivity, pumping test