Estimating Dispersion Coefficient and Porosity from Soil-Column Tests

A simple method for simultaneous and explicit estimation of dispersion coefficient and porosity from laboratory data on soil-column tests is presented. It makes use of the peak derivative of the observed breakthrough curve (BTC). An objective procedure for approximate location of the peak is suggested based upon a parabolic fit through three consecutive points around the peak. The computations involved are simple and can be done on a calculator. The method does not require either the rate of flow or the cross-sectional area of the soil-column for estimating the dispersion coefficient. This completely avoids the possible errors involved in the measurement of these quantities. The new method does not require the full BTC to be observed, however, its application does require data slightly beyond the time at which the exit concentration reaches half the input concentration. Application of the method on a number of laboratory data sets shows that it can yield a reliable estimate of the dispersion coefficient and porosity using only a few points near the peak. The method is applicable for high values (>100) of the piclet number.