Monitoring dielectrical property changes and groundwater velocity changes in a contaminated aquifer using borehole ground penetrating radar and multi-level Point Velocity Probes (PVPs)

A hydrocarbon plume was introduced into a homogeneous aquifer at Canadian Forces Base (CFB) Borden in Canada and a source of oxygen was used to enhance biodegradation of the hydrocarbons. The research objective was to monitor biomass growth and associated groundwater velocity changes during a time-period of enhanced bacterial activity. Dense time-lapse borehole GPR tomographic imaging was used across 14 borehole pairs over a 2x4x5 m monitoring area. The images were used to monitor anomalous dielectric property changes in the aquifer hypothesized to result from biofilm growth and biodegradation of hydrocarbons. Radar wave velocity changes of +/- 4% and attenuation changes of +/- 25% were observed in the data acquired over a period of 22 months. The hydrostratigraphy imaged from GPR was in agreement with groundwater flow variability from Point Velocity Probes (PVPs). Combining these two methods was a valuable tool for recording aquifer properties.; Results show that there are three principle mechanisms that may cause the electrical properties changes observed in the radar data: (1) gas production, (2) mineral dissolution, and (3) direct biofilm growth. Effects of gas production are observed on the eastern half of the monitoring area, while effects of mineral dissolution are seen primarily on the western half. All three mechanisms may occur simultaneously, but since they all have competing effects it is difficult to quantify all three at the same time.