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Description
In order to better understand the applications of the method of induced polarization to the study of ground water, thirty two samples of unconsolidated sediments were analyzed. These samples were characterized by their permeability, mean grain size, standard deviation in grain size, and weight percent clay. Seven electrical parameters are reported. One parameter is the apparent resistivity (R) measured at 0.3 Hz. The two parameters of time domain IP are 3 second chargeability (M3/V) and the ratio of 5 and 20 second chargeability (M5/20). Frequency domain IP is reported as the percent frequency effect (%FE) using R measured at 0.0167 Hz (dc), 0.3 Hz, 5 Hz, 10 Hz and 1000 Hz. The parameters of R0.3 and %FE0.3/1000 were found to have the highest correlation coefficients (0.74 and 0.86 respectively) with clay content. %FE0.3/1000 is a good indicator of changes in all three sedimentary variables. R0.3 correlates well with changes in mean grain size and clay content, but not the standard deviation of grain size. Permeability correlates better with frequency domain IP parameters than either apparent resistivity or time domain IP. The correlation coefficients for the four %FE for permeability and sedimentary variables are found to increase as the frequency ratio increases. %FE parameters calculated with values of R measured with a sine wave have higher correlations to permeability and sedimentary variables than when R is measured using an inverting dc current. Time domain IP parameters generally correlate poorly with the sedimentary variables. However, M3/V does change in response to variations in clay content but not grain size, and M5/20 does change in response to variations in grain size but not clay content. Time domain parameters correlate with permeability only if the changes in permeability are caused by a systematic change in either grain size or clay content but not if both grain size and clay content vary in the same set of samples. When the permeability is controlled by random variations in clay content, grain size and grain size distribution the correlation coefficients for the time domain parameters are as low, or lower than, those for measurements of apparent resistivity alone. For %FE, increasing the difference in the high and low frequencies increases the correlation coefficients for grain size, clay content, and permeability. The %FE0.3/1000 parameter has the best overall correlation to permeability when all sample types are included, with a correlation coefficient of 0.66.
