Case Histories of Hydraulic Conductivity Estimation with IP at the Field Scale

We carried out Induced Polarization (IP) measurements to assess methods previously suggested to estimate hydraulic conductivity from complex electrical conductivity at the field scale. We discuss case histories from four selected sites, covering a lithological spectrum from gravel to silt, with a variation in hydraulic conductivity (k) over three orders of magnitude. At each site, hydraulic conductivity was estimated from the real and imaginary conductivity obtained from 2-D inversion of single-frequency IP data. We applied the constant phase model, where only one frequency, typically around 1 Hz, is used. For the purpose of this study, data from each area were reduced to about 2-3 values only. The IP-determined values are systematically too large when compared to data from grain size analysis or pump tests. For a more detailed investigation, real and imaginary conductivity were displayed vs. hydrogeologically determined k-values. Remarkably, the correlation between the real part and k is better than the correlation of the imaginary conductivity. Thus, the hypothesis that the imaginary part of single frequency IP data improves hydraulic conductivity estimation is not supported by our data.