MEASURING FLUX WITH THE IN-WELL POINT VELOCITY PROBE IN FRACTURED MEDIA

The In-Well Point Velocity Probe (IWPVP) is a novel tool designed for direct, in-situ, and low-cost measurements of groundwater velocity at the centimeter-scale within screened monitoring wells. A miniature tracer test is conducted within the body of the probe that quantifies horizontal flow magnitude and direction. IWPVPs have been validated for use in porous media wells, and recent work has been carried out to validate its use in fractured rock.

Laboratory experiments using a bench-scale model of a single horizontal fracture identified design changes that allowed IWPVP performance in fractured systems to match that in porous media wells. The physical laboratory model was used to show that the probe can accurately determine flow direction and magnitude in a single fracture, as well as determining flux through fractures, using calibration factors.

Field work was carried out at the Edwards Air Force Base, CA, alongside GSI Environmental Inc., involving wells installed in fractured rock. IWPVPs were deployed to create depth profiles of flux and flow direction, and the results compared well, qualitatively, to profiles from the same wells utilizing passive flux meters, FLUTe liners, and oxidation-reduction potentials. These comparisons were initially made qualitatively because conversions from in-probe flux measurements to in-fracture fluxes were still in development.

More recent work, which incorporated data from an acoustic borehole televiewer, used depth-specific estimates of fracture apertures to determine calibration factors for in-fracture flux estimation. This novel advance in the technology provides a means to gain measurement-based estimates of water flux in fractured media.