Identifying transport pathways in fractured rock is extremely
challenging as flow is often organized in a few fractures that occupy a
very small portion of the rock volume. We demonstrate that saline tracer
experiments combined with single-hole ground penetrating radar (GPR)
reflection imaging can be used to monitor saline tracer movement within
mm-aperture fractures. A dipole tracer test was performed in a granitic
aquifer by injecting a saline solution in a known fracture, while
repeatedly acquiring single-hole GPR sections in the pumping borehole
located 6 m away. The final depth-migrated difference sections make it
possible to identify consistent temporal changes over a 30 m depth
interval at locations corresponding to fractures previously imaged in
GPR sections acquired under natural flow and tracer-free conditions. The
experiment allows determining the dominant flow paths of the injected
tracer and the velocity (0.4-0.7 m/min) of the tracer front. Citation:
Dorn, C., N. Linde, T. Le Borgne, O. Bour, and L. Baron (2011),
Single-hole GPR reflection imaging of solute transport in a granitic
aquifer, Geophys. Res. Lett., 38, L08401, doi: 10.1029/2011GL047152.