Monitoring Of Groundwater Pump Tests Using Gpr And Electrical Resistivity

Abstract

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