USING POINT VELOCITY PROBES TO ASSESS SITE CHARACTERIZATION IN A HETEROGENEOUS AQUIFER

Point velocity probes (PVPs) provide direct, centimeter-scale measurements of tracer movement, leading to velocity estimations of flow in granular porous media. A total of 33 PVPs were installed in five multilevel stands in a gravel and sand aquifer near Woodstock, Ontario, Canada. Of the 33 PVPs, 21 were designed with the capability of determining directionality and magnitude of the groundwater velocity in 3-dimensions. The PVPs were used as part of a site characterization effort to help in the design and testing of a cross-injection bioremediation scheme (CIS) for in situ denitrification. The PVP data were consistent with velocities estimated from hydraulic conductivity profiles, based on slug testing, grain-size analyses, and tracer testing. In addition to horizontal flow, the PVPs indicated either upward or downward vertical flow at various locations, trending toward coarser and better-sorted geological material. By assessing the hydraulic gradient from 151 three-point estimators within the monitoring network, two predominant flow directions were identified. However, a single well was determined responsible for all estimators indicating one of those directions. With the removal of the anomalous well from the analysis, horizontal flow directions from the PVPs were found to be consistent with those determined from hydraulic gradient calculations and water-table mapping. It was also concluded from this study that PVPs at this site were able to provide reasonable groundwater velocity estimates within a few days of installation.