EVALUATION OF THE USE OF GROUND PENETRATING RADAR IN THE ANALYSIS OF UNCONFINED AQUIFER PUMPING TESTS

Ground penetrating radar (GPR) imaging of transient water content variations during pumping tests in unconfined aquifers has been performed to varying degrees of success. A previous problem encountered at the CFB Borden site has been that the water drained volume determined from GPR data significantly underestimated the actual water volume pumped from the aquifer. A series of pumping test experiments are currently being performed to determine the source of this discrepancy and evaluate the use of GPR information in pumping test analyses.

In August 2000, a pumping and recovery test was conducted and monitored using an extensive radial array of GPR profile lines. Spatial variation in the GPR data set indicates aquifer anisotropy and heterogeneity - information not available from previous experiments at this site. In addition, direct observations of water content profile drawdown were obtained in a single well using a thermal neutron probe. The drawdown of the GPR reflection correlated with the transition zone was closely followed by the movement of the water content profile. This result suggests that drainage is accurately imaged using GPR profiling. To further test this finding, another pumping test experiment is scheduled for late summer, 2001. This test will involve high resolution GPR profiling along a line of six radially spaced monitoring wells in which neutron water content profiles will be obtained.