Development of a High-Resolution Site Characterization and Dynamic Monitoring Approach Using the Point Velocity Probe Suite of Tools

In environmental monitoring of industrial sites, groundwater flow parameters are typically deduced from aquifer testing and measurements made at several piezometers. The resulting bulk hydraulic properties and hydraulic heads are then used to calibrate numerical models to create conceptual site models. Although research has shown the limitations of these more traditional static conceptual site models, they remain widely used. The project aims to optimize tools for the direct measurement of groundwater velocity, the dominant control on transport of contaminants.

During phase 1 project, the Point Velocity Probe (PVP) and the In-Well PVP (IWPVP) were deployed at a dedicated pilot site within the historical Lacq Industrial Site in Lacq, France. The shallow unconfined aquifer of interest is comprised of complex alluvial deposits associated with the Gave de Pau River. Due to the lack of hydrologic information within the basin, the initial conceptual site model was formulated using a basin wide numerical model indicating seepage (or water pore) velocities generally to the southwest at 2.8 m/d. PVPs were installed in multi-level fashion based on observations made during installations of monitoring wells indicating the possible presence of two fining-upward sequences. IWPVPs were also utilized to collect high-resolution vertical profiles of groundwater velocity in the surrounding monitoring wells in attempt to better assess the depth at which the transition occurred. Both direct groundwater velocity measurement tools indicated the presence of two hydrostratigraphic units with unique groundwater speeds and flow directions. Additionally, the average groundwater velocities observed were consistently less than the groundwater velocity expected based on the initial basin-scale hydrologic model. Based on these findings, focused high-resolution direct groundwater velocity measurements provide a more detailed and dynamic foundation to build an effective conceptual site model that accounts for local geological heterogeneities. Future work is aimed at further developing a full real-time, remote and cost-effective characterization and monitoring solution for building accurate conceptual site models and dynamic monitoring of contaminant plume and remedial progress on operating industrial sites.