Experiences Measuring Groundwater Velocities with PVPs

Groundwater velocity is an essential parameter to know contaminant hydrogeology.    Given the known uncertainty in Darcy Law calculations, stemming from hydraulic conductivity estimation, inherent difficulties in measuring hydraulic gradients in restricted areas or highly permeable aquifers,  and the smaller but noteworthy uncertainty associated with porosity estimation, there is a strong incentive to develop alternate methods.  Over the years, several monitoring well-based instruments have been introduced for this purpose: borehole dilution devices, heat pulse flowmeters, colloidal particle tracking devices, gas diffusion apparatuses.  The ease and low cost of deploying these devices makes them attractive.  However, wells distort the local flow patterns and may obscure vertical flow.  The Vector technology probe, which tracks temperature on a uniformly heated membrane, is installed in direct contact with the aquifer, but is relatively expensive for multiple deployments across a site.  The PVP is an inexpensive device suitable for multiple deployments in non-cohesive aquifers, and is not affected by well biases – though careful installation is required to minimize aquifer disturbances next to the probe.  The PVP has evolved from a piecewise construction to a single piece unit manufactured on a prototype printer.  PVPs have been found sensitive enough to detect flow variations that would be impossible to detect from hydraulic head measurements.