Coupling High-Resolution Acoustic Sensor Measurements with Analytical and Numerical Porous Media Solute Transport Modeling

This paper presents the development of a novel acoustic sensor that enhances Doppler approaches to monitor groundwater vector flow. The technique is based on a high-resolution acoustic phase measurement: flowing water introduces a shift in the acoustic velocity component between the transmitter and receiver. By switching the transmitter and receiver modes at periodic intervals, the resulting magnitude of the acoustic phase shift yields the speed of water flow. The high-resolution of the measurement comes from the feedback loop architecture that forces an output toneburst to the transmitter to remain in quadrature with the signal recorded at the receiver. Flow velocity measurements in a column filled with saturated sand (subjected to salt tracer injections), were validated in an ASTM standard constant-head hydraulic test column. Several analytical solution solute transport models and a finite-element numerical model were applied to the test column and compared with measured data. Model predictions obtained before the actual experiments were conducted were very useful to determine expected salt breakthrough curves. The models were subsequently calibrated after the laboratory data were recorded. Results presented clearly indicate the importance of selecting models that incorporate appropriate boundary conditions.