STOCHASTIC AND DETERMINISTIC ANALYSIS OF DISPERSION IN UNSTEADY-FLOW AT THE BORDEN TRACER-TEST SITE, ONTARIO, CANADA

In this work, recently collected water-level data from the Borden aqui fer are applied to two recent models to determine whether they predict the observed horizontal transverse dispersion observed at the aquifer . The collected water-level data are first detrended using a combinati on of ordinary least-squares and generalized least-squares methods. Th e trend surface information shows that the hydraulic head gradient is transient. A geostatistical analysis is performed on the time series o f the components of the hydraulic head gradient to determine the varia nces and integral scales present. Assuming the data represent earlier behaviour at the aquifer, the results of the geostatistical analysis a re combined with those obtained from the Stanford Waterloo tracer expe riment and the combination used to evaluate Rehfeldt's equations for t he asymptotic macrodispersivity due to unsteady flow conditions. The c omputed range in asymptotic transverse horizontal macrodispersivity is found to be 0.0014 m less-than-or-equal-to A22 less-than-or-equal-to 0.054 m. This computed range is in good agreement with the measured di spersivity values for the Borden aquifer. Spectral analysis is also pe rformed on the component of hydraulic head gradient perpendicular to t he mean flow direction and these results, along with those obtained fr om the Stanford Waterloo tracer experiment, are incorporated into Naff et al.'s moment model to predict the horizontal transverse moments at the site. The moments, computed using Naff et al.'s model, are found to significantly under-predict the observed moments at the site. The a nalysis shows that flow transients contribute to the transverse macrod ispersion at the Borden site.