Monitoring Of Groundwater Pump Tests Using Gpr And Electrical Resistivity

Ground-penetrating radar (GPR) and electrical resistivity surveys were used to monitor<br>two aquifer pump tests conducted at a test site near Boston, Massachusetts. Measurements of<br>drawdown were made both during and after each pumping test. Distance-drawdown experiments<br>were conducted in which GPR profiles and electrical resistivity pseudo-sections were used in an<br>attempt to image the depth to the water table (or the top of the capillary fringe). Although<br>differences could be observed between the profiles collected at maximum drawdown and at full<br>recovery, we have not yet been able to uniquely identify the phreatic surface and map the cone of<br>depression. Time-drawdown experiments using both electrical resistivity soundings and<br>stationary GPR measurements have proven to be more effective in directly imaging the depth to<br>the “water table”. In particular, we have been able to use GPR measurements made as a function<br>of time at a fixed location to estimate the conductivity of the aquifer. Increased processing and<br>inversion of the GPR profiles and resistivity pseudo-sections may enhance the analysis of the<br>distance-drawdown data. It may also be possible to use the time-drawdown data to facilitate the<br>location of the “water table” in the distance-drawdown measurements.