Monitoring Of A Pumping Test In An Unconfined Aquifer With Ground Penetrating Radar

The temporal and spatial response of an unconfined aquifer at CFB Borden to a pumping<br>test was monitored by means of ground-penetrating radar (GPR) profiling. The reflection<br>caused by changing water content in the transition zone between the overlying residually<br>saturated material and the water saturated aquifer below was used to estimate the location of<br>the top of the water saturated zone (TWSZ). Observed depth variations in the TWSZ<br>reflection differed significantly from the water table drawdown measured in the piezometers.<br>The GPR results are consistent with the in-situ water content measurements of Nwankwor et<br>al. (1992) and support their proposed delayed drainage mechanism. Diffractions along the<br>TWSZ reflection indicate that differential drainage due to small scale variations in aquifer<br>properties occurs. Arrival time variations of reflections from underlying stratigraphic<br>horizons are accounted for by changes in the overlying velocity structure caused by the<br>lowering of the TWSZ.