Monitoring Air Sparging In The Cfb Borden Aquifer Using Gpr Reflection Surveys, Borehole Gpr And Geophysical Well Logging

Abstract

Air sparging is a groundwater remediation technique that introduces air into the subsurface to enhance the removal of contaminants. The effective application of this technique requires a knowledge of the spatial distribution and magnitude of air saturation achieved during the sparging process. This paper discusses the use of ground penetrating radar (GPR) reflection surveys, borehole GPR, and geophysical well logging techniques to determine the steady state air saturation distribution within a sandy aquifer during an air sparging experiment performed at Canadian Forces Base (CFB), Borden, Ontario. Air was injected at a depth of 3 m below the water table using a flow rate of 200 m3/day (5 scfm). Surface GPR reflection surveys, borehole GPR surveys and geophysical well logs were acquired prior to the injection of air, and after the eighth day of sparging. GPR reflection surveys, sensitive to changes in air saturation with depth, mapped large flat lying pockets of trapped air, that had moved to, and presumably past, the edges of the test site. Borehole GPR surveys and neutron logging provided quantitative estimates of air saturation throughout the test cell, giving maximum air saturations of 60% near the centre of the test area and 20% at the edges. Electromagnetic (EM) induction logs indicated that as a result of surface water pumping, more conductive water from a deeper inorganic plume moved into the zone being sparged, but could not be used to determine air saturation.